USE OF DENDROASPIN AS A VEHICLE FOR NON-DENDROASPIN DOMAINS

Abstract: The use of dendroaspin as a scaffold for one or more non-wild-type dendroaspin domains, the dendroaspin scaffold being modified in that the native RGD motif has been deleted or has been replaced by (i) an amino acid sequence having no integrin-binding activity or (ii) an integrin-binding amino acid sequence other than RGD which contains aspartic acid (D) or glutamic acid (E).

Description: USE OF DENDROASPIN AS A VEHICLE FOR NON-DENDROASPIN DOMAINS FIELD OF THE INVENTION The present invention relates to molecules comprising modified dendroaspin scaffolds and in particular to the use of modified dendroaspin as a vehicle for non-dendroaspin domains. BACKGROUND OF THE INVENTION The role of blood coagulation is to provide an insoluble fibrin matrix for consolidation and stabilisation of a haemostatic plug (blood clot). Formation of a cross-linked fibrin clot results from a series of biochemical interactions involving a range of plasma proteins. Acute vascular diseases, such as myocardial infarction, stroke, pulmonary embolism, deep vein thrombosis and peripheral arterial occlusion are caused by either partial or total occlusion of a blood vessel by a blood clot. The formation of a blood clot within a blood vessel is termed thrombosis and is dependent upon platelet aggregation. In the context of blood vessel injury (such as that which might arise in surgical procedures), the interaction of blood platelets with the endothelial surface of injured blood vessels and with other platelets is a major factor in the course of development of clots or thrombi. Platelet aggregation is dependent upon the binding of fibrinogen and other serum proteins to the glycoprotein receptor Ilb/IIIa complex on the platelet plasma membrane. Glycoprotein GP Ilb/IIIa is a member of a large family of cell adhesion receptors known as integrins, many of which are known to recognise an Arg-Gly-Asp (RGD) tripeptide recognition sequence. Integrins are a family of cell surface receptors that mediate adhesion of cells to each other or to extracellular matrix substrate (1-5). They are composed of non-covalently associated α and β transmembrane subunits selected from among 16α and 8β subunits that heterodimerise to produce 20 receptors (6). Among the integrins, the platelet membrane α jj β3 is the best characterised (3, 5). Upon cell activation, the TT^ integrin binds several glycoproteins, predominantly through the Arg-Gly-Asp (RGD) tripeptide sequence (6-8) present in fibrinogen (9), fibronectin (10), von Willebrand factor (11), vitronectin (12) and thrombospondin (13). The nature of the interactions between these glycoprotein ligands and their integrin receptors is known to be complex with conformation changes occurring in both the receptor (14) and the ligand (15). The practical effect of such interactions can be illustrated by considering the treatment of localised narrowing of an artery caused by atherosclerosis. This is a condition which can usually be remedied surgically by the technique of ballon angioplasty. The procedure is invasive and causes some tissue damage to the arterial wall which can result in thrombus formation. Extracellular proteins such as fibronectin in the arterial wall become exposed to blood in the artery. Platelets bind to the RGD motif of fibronectin via integrin receptors which in turn leads to platelet aggregation and the start of the cascade of clotting reactions. An agent which specifically inhibits platelet aggregation at the sites of damage and which also inhibits clotting at these sites is required. The agent should be non-toxic and free of undesirable side effects such as a risk of generalised bleeding. Various agents for preventing formation of blood clots are now available, such as aspirin, dipyridamole and filopidine. These products generally inhibit platelet activation and aggregation, or delay the process of blood coagulation, but they have the potential side effect of causing prolonged bleeding. Moreover, the effect of such products can be reversed only by new platelets being formed or provided. Therefore, the development of antagonists towards selected cell adhesion events would be of significant clinical utility in the treatment of thrombosis and atherosclerosis. A key cell adhesion mechanism common to a number of integrin-ligand interactions involves the recognition of aspartic acid (D)-containing sequences or motifs identified by the use of inhibitory synthetic peptide analogues including RGD, KGD, LDV, KQAGDV. However, these peptides are limited by low potency and specificity. In this regard, a major breakthrough has been the discovery of a family of small, RGD-containing proteins derived from snake venoms termed disintegrins. Scarborough et al (17) have reported a naturally occurring KGD-containing snake protein isolated from the venom of Sistrurus M. Barbourϊ termed barbourin showing a GPIIb-IIIa specific integrin antagonist activity. Recently, many proteins from a variety of snake venoms have been identified as potent inhibitors of platelet aggregation and integrin dependent cell adhesion. The majority of these proteins which belong to the disintegrin family share a high level of sequence homology, are small (4-8 kDa), cysteine rich and contain the sequence RGD (16) or KGD (17). In addition to the disintegrin family, a number of non-disintegrin RGD proteins of similar inhibitory potency, high degree of disulphide bonding and small size, have been isolated from both the venoms of the Elapidae family of snakes (18, 19) and leech homogenates (20). All of these proteins are approximately 1000 times more potent inhibitors of the interactions of glycoprotein ligands with the integrin receptors than simple linear RGD peptides - a feature that is attributed to the optimally favourable conformation of the RGD motif held within the protein scaffold. The NMR structures of several inhibitors including kistrin (21-23), fiavoridin (24), echistatin (25-28), albolabrin (29), decorsin (30) and dendroaspin (31, 32) have been reported and the only common structural feature elucidated so far is the positioning of the RGD motif at the end of a solvent exposed loop, a characteristic that is of prime importance to their inhibitory action. Dendroaspin, therefore, is a natural variant of the short neurotoxin family, but contains the adhesive tripeptide Arg-Gly-Asp (RGD) and functions as a potent antagonist of integrin- mediated cell adhesive interactions. Dendroaspin was originally isolated from the venom of the Elapidae snake Dendroaspis jamesonii (Jameson's mamba) as a potent inhibitor of platelet aggregation and integrin mediated platelet adhesion. The activity of dendroaspin is due to an RGD motif contained within a solvent-exposed loop. International patent application WO 98/42834 describes amongst other things bi- or multi-functional molecules based on a dendroaspin scaffold, in which, in addition to integrin-binding function, a second function is achieved by adding a domain of another protein to a dendroaspin scaffold. WO 98/42834 and its entire content is included herein by reference. As is described in WO 98/42834, the dendroaspin molecule has 59 amino acid residues and comprises 3 loops. Loop I comprises amino residues 4-16, loop II residues 23-36 and loop III residues 40-50; it is loop III which contains the RGD motif in wild-type dendroaspin. The RGD domain forms residues 43-45. SUMMARY OF THE INVENTION The following abbreviations are used in this specification: Hvdrophobic amino acids A = Ala = alanine V = Val = valine I = He = isoleucine L = Leu = leucine M = Met = methionine F = Phe = phenylalanine P = Pro = proline W = Trp = tryptophan Polar (uncharged) ammo acids N = Asn = asparagme C = Cys = cysteme Q = Gin = glutamme G = Gly = glycme S = Ser = seπne T = Thr = threonme Y = Tyr = tyros e Positively charged ammo acids R = Arg = arginme H = His = histidme K = Lys = lysine Negatively charged am o acids D = Asp = aspartic acid E = Glu = glutamic acid The present invention relates to products comprising a modified dendroaspin scaffold. The dendroaspin scaffold has been found to form a stable vehicle for non-dendroaspm moieties and to be useful for this purpose irrespective of whether the modified scaffold retains the RGD sequence or, indeed, any integrin-binding activity at all. Molecules comprising a dendroaspin scaffold in which the RGD motif has been replaced by another integrin-binding motif but to which no further functional sequence has been added are useful scientific tools, for example for the study of receptor interactions, as can be polypeptides comprising a dendroaspin scaffold in which the RGD motif has been deleted or replaced by a πon-integπn-binding motif. DETAILED DESCRIPTION OF THE INVENTION The invention relates preferably to the use of a dendroaspin scaffold as a vehicle for one or more non-wild-type dendroaspin domains, the dendroaspin scaffold being modified as compared with wild-type dendroaspin in that the native RGD motif has been deleted or has been replaced by (i) an ammo acid sequence having no integrin-binding activity or (n) an integrin-binding ammo acid sequence other than RGD which contains aspartic acid (D) or glutamic acid (E), e.g KGD. The dendroaspin scaffold may have additional modifications as described in more detail below. The present invention further provides in one aspect a product comprising a dendroaspin scaffold in which the native RGD motif has been deleted or has been replaced by a replacement ammo acid sequence In one class of products, the replacement ammo acid sequence is an ammo acid sequence having no integrin-binding activity. In another class of products, the replacement ammo acid sequence is an integrin-binding ammo acid sequence and comprising a tripeptide sequence other than RGD containing D or E adjacent to G or to a hydrophobic ammo acid. Throughout the description and claims of this specification, the word "comprise" and variations of the word, such as "comprising" and "comprises", means "including but not limited to," and is not intended to exclude other components, integers, additives or steps. The invention includes products or hybrid polypeptides which comprise a dendroaspin scaffold and which have an integrin-binding ammo acid sequence other than RGD which contains aspartic acid (D) or glutamic acid (E) (and preferably is as defined in the previous paragraph) at one domain and a non-dendroaspm species which confers a second functionality on another domain. The non-dendroaspm ammo acid sequence may be comprised in the loops of the scaffold or be wholly or partially external to the loops. The polypeptide may be one in which the residues of a non-loop region of the dendroaspin scaffold are augmented by the non- dendroaspm ammo acid sequence, e.g. by ligatmg the non-dendroaspm ammo acid sequence directly or through a linker to a terminal sequence of the dendroaspin scaffold. The linker may be a peptide or a non-peptide structure; the non-dendroaspm species is a moiety not found in dendroaspin and typically an ammo acid sequence not found in dendroaspin. In preferred products the tripeptide sequence is of the formula B-J-Z wherein (I) J-Z is GD or GE and B is R, K, Q, A, H, N, A, V, I, L, M, F, P or W but is not R when J-Z is GD; (II) B-J is DG or EG and Z is any ammo acid; or (III) J is D or E and B and Z are each independently selected from A, V, I, L, M, F, P or W Preferably J-Z is GD and, in the products in which J-Z is GD or GE, B is preferably R, K, Q, A, H or N and more preferably is R, K, Q or A (but is not R when J-Z is GD). A preferred class of products (I) comprises those in which B-J-Z is bonded at its C-termmal end to M, W, N or V. Preferably the M, W, N or V residue is followed by the P which is at position 47 of wild type dendroaspin or by an A residue substituted therefor Another preferred class of products (I) comprises those in which the integrin-binding amino acid sequence is preceded by the P which is at position 42 of wild type dendroaspin or by an A residue substituted therefor. In some preferred products (I), especially those in which J-Z is GD, B is A, V, I, M, F, P, W and more preferably is L or V. The most preferred products of this type are those in which B is L and is preceded by M. Preferred products (II) include those in which B-J is DG and/or Z is E, R or P, and especially in which Z is followed by the P which is at position 47 of wild type dendroaspin or by an A inserted before the wild type position 47 P. A preferred class of products (III) comprises those in which J is D and, more particularly, B-J-Z is LDV. B-J-Z is preferably preceded by an I residue. If the RGD motif is replaced by a non-integrin-binding sequence, the replacement sequence may in principle be any sequence which permits a dendroaspin-like configuration to remain, for example it may be a non-dendroaspin domain as described in more detail later in this specification. Of course, the modified dendroaspins of the invention will often have a configuration which differs somewhat from that of wild-type dendroaspin but do normally have a three-loop structure. Preferably, the RGD-replacement associates with a receptor pocket or another pocket, since loop III is favourable for pocket-binding sequences; such sequences include a thrombin-binding sequence (GPRP is a thrombin-binding sequence) and the collagen α 2 β -binding sequence DGE. In addition to having a deleted or replaced RGD motif, the products or polypeptides of the invention usually comprise at least one non-wild-type dendroaspin domain elsewhere than the native RGD site. The at least one non-wild-type dendroaspin domain usually comprises at least one non-dendroaspin sequence which confers functionality on the polypeptide. One class of products have an integrin-binding activity which, when product molecules are administered in vivo, results in the binding of the molecules to platelets thereby inhibiting the aggregation of the platelets at sites of injury. In these products, the RGD motif has been replaced by another platelet-binding sequence, especially KGD. In addition to containing an integrin-binding domain, the products of this class preferably contain another non-wild-type dendroaspin domain which provides secondary, optionally further, functionality e.g. antithrombotic action, inhibition of cell migration and/or proliferation, or regulation of signal transduction. Molecules of this class of the invention are therefore bi- or multi-functional in their activities, and preferably are bi- or multi-functional in their activities against blood coagulation, particularly thrombus formation and arterial/venous wall thickening at the sites of injury. Products of the invention may have activity against leukocyte recruitment, immune system activation, tissue fibrosis or tumorigenesis. Those skilled in the art are familiar with peptide and peptidomimetic inhibitors of serine proteases (e.g. elastase, cathepsin G, urokinase (also called uPA), Factors II, IX, X, VII, IXa and XII thrombin, kallikrein, tissue plasminogen activator and plasmin) and the non-wild-type domain may comprise such an inhibitor. The product may comprise at least two non-wild-type dendroaspin domains, said domains optionally having the same sequence. Optionally, the molecules of the invention include a dendroaspin scaffold containing a non-wild- type dendroaspin domain which comprises two or more amino acid sequence portions separated by at least one amino acid residue of dendroaspin. The two or more sequence portions may be transposed with respect to one another and to the linear order of amino acids in the native non- dendroaspin amino acid sequence. In other words, the native order of the two or more amino acid sequence portions may be altered without the actual sequence of each portion necessarily being altered (although the sequence of at least one portion may be modified). Most products of the invention contain a domain not found in wild-type dendroaspin, i.e. a non- wild-type dendroaspin domain. The non-wild-type domain usually confers a function on the molecule, although in the case of molecules prepared for the purpose of scientific studies the domain may not always confer a function. The functionality conferred by the non-wild-type domain is not critical to the invention and in principle may be any function capable of being conferred by an amino acid sequence which can be incorporated in the dendroaspin scaffold, by, for example, insertion into the dendroaspin scaffold, or ligation to either the N- or C-terminal ends thereof. For example, and especially when it has the RGD motif replaced by a D or E- containing motif conferring platelet-binding activity, the products may contain a non-wild-type dendroaspin domain comprising a sequence conferring platelet derived growth factor (PDGF) activity, glycoprotein IBα activity, hirudin activity, thrombomodulin activity, vascular epidermal growth factor activity, transforming growth factor-βl activity, basic fibroblast growth factor activity, angiotensin II activity, factor VIII activity, tissue factor pathway inhibitor (TFPI) von Willebrand factor activity, tick anticoagulant protein (TAP) activity or nematode anticoagulant protein (NAP) activity. The non-wild-type dendroaspin domain typically comprises a sequence derived from platelet derived growth factor (PDGF), glycoprotein IBα, hirudin, thrombomodulin, vascular epidermal growth factor, transforming growth factor-βl, basic fibroblast growth factor, angiotensin II, factor VIII, tissue factor pathway inhibitor (TFPI), von Willebrand factor, TAP or NAP (e.g. NAP5), or a functional sequence having homology to at least part of such sequence Such functional sequences may share about 50% ammo acid sequence homology, preferably about 65%, more preferably about 75% and even more preferably about 85% homology with dendroaspin. In this way the molecules of the invention may be rendered multifunctional so that they are active against, for example, platelet aggregation and another component in the clotting cascade (e.g. a seπne protease coagulation enzyme, for example thrombm), or the mtracellular signalling cascade (e.g. growth factor). The bi- or multi-functional products of the invention may be engineered to contain a said non-wild-type domain having integrin-binding activity in addition to an integrin-binding RGD replacement (X-Y-Z), thereby providing a dendroaspm-based molecule with augmented integrin-binding activity The invention includes of course dendroaspm-based molecules which contain no integrin-binding function and molecules with no anti-coagulant function. The products of the invention preferably comprises an am o acid sequence as shown in Figure 1 Excluding said further am o acid sequence, the products of the invention include polypeptides comprising dendroaspin scaffolds homologous to wild-type dendroaspin which may share about 50% or more am o acid sequence homology, preferably about 65% or more, more preferably about 75% or more and even more preferably about 85% or more homology with dendroaspin. The polypeptides of the invention may comprise a greater or lesser number of am o acid residues compared to the 59 ammo acids of dendroaspin. For example, the molecules of the invention may comprise a number of am o acid residues in the range 45 to 159, preferably about 49 to 89, more preferably about 53 to 69, even more preferably about 57 to 61. However, the invention includes polypeptides containing an incorporated foreign sequence which replaces a native sequence of the same length, i.e. the one or more non-wild-type domains are the same size as the native domains they replace; if the RGD motif is replaced by a tripeptide sequence (e.g. KGD) such polypeptides will of course have 59 ammo acid residues. Preferred polypeptides comprise an am o acid sequence as shown in Figure 1. The invention includes species in which a foreign sequence is contained wholly within the dendroaspin scaffold (i.e. between residues 1 and 59, inclusive) and is for example loop grafted Thus, in one class of products, said non-wild-type domaιn(s) is/are incorporated into (a) loop I and/or loop II; (b) loop I and/or loop III; (c) loop II and/or loop III; or loop I, loop II and loop III of the dendroaspin scaffold. If the polypeptide comprises a non-wild-type domain incorporated into a loop, the non-wild-type domain is in some polypeptides incorporated into either loop I or loop II, leaving loop III unaltered. Another class, however, comprises the polypeptides which comprise a non-wild-type domain extending into or substituting regions external to the loops, i.e. residues 1-3, 17-22, 37-39 and 51-59 such that residues of the non-loop regions are augmented or substituted for those of a further ammo acid sequence being inserted (the non-wild-type domain), for example, the inserted sequence (or one or more of a plurality of inserted sequences) may be ligated directly or via a linker to a residue of the C- or N- terminal non-loop region of the dendroaspin scaffold. The invention thus provides a hybrid dendroaspm-based polypeptide comprising in its dendroaspin portion a first ammo acid sequence conferring platelet-binding activity in place of RGD, and a further ammo acid sequence conferring another activity (for example, anti- thrombotic activity), said first sequence being one other than than RGD which contains aspartic acid (D) or glutamic acid (E) and the non-dendroaspm ammo acid sequence being external to the loops and augmenting the residues of a non-loop region of the dendroaspin portion, for example by gation to a terminal portion of the dendroaspin portion (dendroaspin-deπved moiety) One preferred location for the foreign non-wild-type sequence is at a site in the dendroaspin scaffold between ammo acid residues: 4-16, 18-21 or 23-36, or at a site forming the C-terminus or N-termmus of the polypeptide Thus the non-wild-type sequence may be created before residue 4 (for example, before residue 1) or at the end of the dendroaspin scaffold after residue 50, e.g. after one of residues 52 to 59. The foreign ammo acid sequence may be linked to the N- or C- terminal am o acid of the wild type dendroaspin either directly or through a linker, which is preferably but not necessarily a polypeptide linker Any linker may optionally be designed so that it adopts a conformation which avoids or reduces interference between the functional domain of the foreign sequence and the dendroaspin scaffold as well as interference between any functional domain in the dendroaspin scaffold and the foreign sequence Foreign sequences which form a terminus may extend into a loop, e g. although foreign sequences which form the C-termmus may be inserted in their entirety after residue 50, they may alternatively commence in or before loop III, e g at residue 37, 38, 39, 40 or 41 or later (e g at residue 47). Each inserted non-wild-type domain or portion of a non-wild-type domain is preferably an ammo acid sequence having no more than 100 ammo acid residues, e g from 3 to 40 ammo acid residues Especially in the case of inserted sequences which are contained wholly within the dendroaspin scaffold, the non-wild-type domain more preferably has from 3-16, even more preferably 3-14 ammo acid residues The start of the inserted further ammo acid sequence (non-wild-type domain) may be before ammo acid residue 1 of the dendroaspin molecule or it may be at any one of ammo acid residues 1-57 of the dendroaspin scaffold The end of the inserted ammo acid sequence may be at any one of the ammo acid residues 3-59 of the dendroaspin scaffold, or the insetted sequence may extend beyond the position of residue 59 When two non-wild-type domains are incorporated into the dendroaspin scaffold then the linear distance between these is preferably from 1-35 ammo acids, more preferably 1-14 ammo acids When more than two non-wild-type domains are incorporated then there is preferably at least one native dendroaspin ammo acid residue separating each further ammo acid sequence Loop III may be modified by insertion, deletion or substitution of any one or more ammo acid residues, preferably a maximum of 8 or a minimum of 1 ammo acids can be modified within loop III of dendroaspin, e g. 1, 2, 3 or 4. An integrin-binding sequence (e.g KGD or RGD motif) may be incorporated into the dendroaspin scaffold at a place other than the wild-type RGD domain, preferably into loop I or loop II The molecules of the invention in which RGD is replaced may comprise a loop III having an ammo acid sequence flanking the RGD site modified from that flanking RGD in wild-type dendroaspin, for example modified as shown in Figure 3B of WO 98/42834. An advantage of modifying the flanking region is that the activity of the B-J-Z sequence (e.g. integrin-binding activity) may be enhanced or become more specific for certain glycoprotein ligands Also, if one or more of the "foreign" further ammo acid sequences grafted into the dendroaspin scaffold has steric effects on a replacement ammo acid sequence for RGD then loop III around the RGD domain (occupied by B-J-Z) can be modified to overcome any steric hindrance thereby restoring, perhaps enhancing, functionality at the RGD domain. Especially if the replacement ammo acid sequence has more than 3 residues, ammo acids flanking the RGD site may be deleted, for example so that the number of ammo acid residues in loop III remains as 13 Loop I or loop II may be modified by insertion, deletion or substitution of one or more ammo acid residues. Any suitable number of am o acids (e g up to 100 or more) can be incorporated into the dendroaspin scaffold to give, for example, a desired bi- or multi-functional activity although a number of residues in the range 14 to 36 are preferred for incorporation at one or more sites contained in the dendroaspin scaffold. Modification of the dendroaspin loops may become necessary if a "foreign" further amino acid sequence incorporated into the dendroaspin scaffold has a steric hindrance effect either on another incorporated domain or on the loop III. Computer assisted molecular modelling using Insight II software (Molecular Simulations Inc) can be used to predict the structure of the "loop grafted" dendroaspins of this invention. In instances where steric effects between the loops may serve to cause loss of functionality, these effects can be "designed out" by modifying appropriate parts of the dendroaspin molecule in an appropriate way. Sometimes this may involve incorporating a number of suitable amino acid residues to extend one or more of the loop structures. Preferred modification includes the incorporation of polyglycine into the loop or loops of the dendroaspin scaffold in order to extend them. Other modifications comprising repeat units of an amino acid residue or number of residues can be used. Computer modelling studies can be used to design the loop modifications needed in order to extend the loops of dendroaspin. Further modifications may also be necessary to ensure that a non-wild-type domain does not inhibit the function of another domain located on the dendroaspin scaffold. In the design of a bi-functional or multi-functional molecule in accordance with the invention, "fine tuning" of activity, stability or other desired biological or biochemical characteristic may be achieved by altering individual selected amino acid residues by way of substitution or deletion. Modification by an insertion of an amino acid residue or residues at a selected location is also within the scope of this "fine tuning" aspect of the invention. The site-directed mutagenesis techniques available for altering an amino acid sequence at a particular site in the molecule will be well known to a person skilled in the art. PREPARATION The products of the invention comprise, and preferably are, polypeptides which may be made by construction of appropriate expression vectors, e.g. polynucleotides comprising a coding sequence operatively linked to a promoter. The skilled person can readily construct a variety of clones containing functional nucleic acids. Cloning methodologies to accomplish these ends, and sequencing methods to verify the sequences of nucleic acids, are well known in the art. Examples of appropriate cloning and sequencing techniques, and instructions sufficient to direct persons of skill through many cloning exercises are found in Sambrook, et al., Molecular Cloning: A Laboratory Manual (2nd Ed., Vols. 1-3, Cold Spring Harbor Laboratory (1989)), Methods in Enzymology, Vol. 152: Guide to Molecular Cloning Techniques (Berger and Kimmel (eds.), San Diego: Academic Press, Inc. (1987)), or Current Protocols in Molecular Biology, (Ausubel, et al. (eds.), Greene Publishing and Wiley-Interscience, New York (1987). Product information from manufacturers of biological reagents and experimental equipment also provide information useful in known biological methods. Such manufacturers include the SIGMA chemical company (Saint Louis, MO), R&D systems (Minneapolis, MN), Pharmacia LKB Biotechnology (Piscataway, NJ), CLONTECH Laboratories, Inc. (Palo Alto, CA), Chem Genes Corp., Aldrich Chemical Company (Milwaukee, WI), Glen Research, Inc., GIBCO BRL Life Technologies, Inc. (Gaithersberg, MD), Fluka Chemica-Biochemika Analytika (Fluka Chemie AG, Buchs, Switzerland), Invitrogen, San Diego, CA, and Applied Biosystems (Foster City, CA), as well as many other commercial sources known to one of skill. Polynucleotides containing a desired gene can be prepared by any suitable method including, for example, cloning and restriction of appropriate sequences as discussed supra, or by direct chemical synthesis by methods such as the phosphotriester method of Narang et al. Meth. Enzymol. 68: 90-99 (1979); the phosphodiester method of Brown et al., Meth. Enzymol. 68: 109-151 (1979); the diethylphosphoramidite method of Beaucage et al., Tetra. Lett., 22: 1859- 1862 (1981); the solid phase phosphoramidite triester method described by Beaucage and Caruthers (1981), Tetrahedron Letts., 22(20): 1859-1862, e.g., using an automated synthesizer, e.g., as described in Needham-VanDevanter et al. (1984) Nucleic Acids Res., 12:6159-6168; and, the solid support method of U.S. Patent No. 4,458,066. Chemical synthesis produces a single stranded oligonucleotide. This may be converted into double stranded DNA by hybridization with a complementary sequence, or by polymerization with a DNA polymerase using the single strand as a template. One of skill would recognize that while chemical synthesis of DNA is limited to sequences of about 100 bases, longer sequences may be obtained by the ligation of shorter sequences. Nucleic acids may be modified by site-directed mutagenesis, as is well known in the art. Native and other nucleic acids can be amplified by in vitro methods. Amplification methods include the polymerase chain reaction (PCR), the ligase chain reaction (LCR), the transcription-based amplification system (TAS), the self-sustained sequence replication system (SSR). A wide variety of cloning methods, host cells, and in vitro amplification methodologies are well-known to persons of skill. As described in WO 98/42834, the wild type dendroaspin gene may be successfully inserted into a plasmid pGEX-3X (Figure 2 of WO 98/42834) and expressed according to the method of Lu et al, (1996) J Biol Chem 271: 289-295. Starting with the wild type gene for dendroaspin, variants of the dendroaspin gene for expressing polypeptides of the invention may then be engineered using recombinant DNA technology. For the longer insertion variants, oligonucleotides which encode the non-dendroaspin or heterologous amino acids may simply be inserted directly into suitably restriction digested wild type dendroaspin gene and then ligated. For minor changes such as modification of a few amino acid residues including the insertion, substitution or deletion, site directed mutagenesis may be used, for example using the Transformer™ Site- Directed Mutagenesis kit from Clontech Laboratories in accordance with the manufacturer's instructions. As an alternative to modifying the wild type gene after insertion into an expression vector, as described above with reference to plasmid pGEX-3X, genes encoding polypeptides of the invention may be made by methods which comprise the construction of vectors containing non- wild-type genes by ligation of oligonucleotides optionally followed by modification by, in particular, site-directed mutagenesis. Figure 2A of WO 98/42834 shows the nucleotide sequence of the synthetic dendroaspin (Den) gene. The gene was designed on the basis of the known amino acid sequence (Williams J A et al ((1992)) Biochem Soc Trans 21: 73S) and the codons for each amino acid were adopted from those which were highly expressed in E cσ// (Fiers W ((1982)) Gene 18: 199-209) Ten synthetic oligonucleotides are shown in brackets and numbered individually 1 to 10 either above the coding strand or below the non-coding strand. The stop codon is indicated by an asterisk. Three-letter amino acid code is used and the total of 59 amino acids of Den are only numbered 1 for N-terminal residue arginine and 59 for C-terminal leucine. In an additional aspect, therefore, the invention resides in nucleic acid molecules encoding a polypeptide of the invention. The nucleic acid may be operatively linked to a promoter and optionally to a nucleic acid sequence encoding a heterologous protein or peptide thereby to encode a fusion product. Suitably the promoter is IPTG inducible and optionally the heterologous protein or peptide is glutathione S-transferase. Excluding the nucleic acid sequence encoding said further non-wild-type domain, nucleic acid sequences encoding the polypeptides of the invention may share about 50% nucleotide sequence homology, preferably about 65%, more preferably about 75% and even more preferably about 85% homology with a dendroaspin nucleotide sequence. The invention includes plasmids comprising a nucleic acid of the invention, for example plasmid pGEX-3X comprising a nucleic acid of the invention, as well as host cells transformed with such a plasmid. A suitable host cell is E coli. The host cells may be provided as cell cultures. Another aspect of the invention resides in a method of producing a polypeptide comprising culturing a host cell of the invention so as to express said polypeptide, extracting the polypeptide from the culture and purifying it. The invention further includes a method of producing a polypeptide comprising a dendroaspin scaffold, the method comprising: a) preparing an expression vector comprising a nucleic acid sequence encoding a dendroaspin scaffold of the invention operatively linked to a promoter and optionally linked to a nucleic acid sequence encoding a heterologous protein for co-expression therewith; and b) transforming a host cell with the vector and causing the host cell to express the modified dendroaspin nucleic acid sequence. Some of these methods comprise a) (i) assembling from overlapping oligonucleotides the coding sequence of a dendroaspin scaffold containing an RGD motif and operatively linking the resulting cDNA to a promoter, the promoter optionally being linked to a nucleic acid sequence encoding a heterologous protein for expression of fusion protein; and a) (ii) modifying the RGD-encoding domain of the expression vector to encode a dendroaspin scaffold in which RGD has been deleted or replaced by a replacement amino acid sequence as defined herein. In such methods, step (a) (ii) may comprise, before or after said modification, modifying at least one other domain of the nucleic acid sequence of the vector encoding the dendroaspin scaffold by one or more of the insertion, deletion or substitution of nucleic acid residues so that on expression the dendroaspin scaffold comprises a corresponding domain having a non-wild- type dendroaspin sequence. Others of the methods comprise constructing from oligonucleotides an expression vector comprising a nucleic acid sequence encoding a dendroaspin sequence in which the RGD- encoding domain has been deleted or replaced by a replacement amino acid sequence as defined herein and, optionally, modifying at least one other domain of the nucleic acid sequence of the vector encoding the dendroaspin scaffold by one or more of insertion, deletion or substitution of nucleic acid residues so that on expression the dendroaspin scaffold comprisess a corresponding domain having a non-wild-type dendroaspin sequence. The method may comprise the steps of: a) extracting the modified dendroaspin from a host cell culture, b) purifying the modified dendroaspin from the cell culture extract, and, if the modified dendroaspin is a fusion protein, cleaving the dendroaspin portion from the heterologous portion of the fusion protein. The heterologous protein is suitably glutathione S-transferase (GST) and the purification suitably involves GST affinity chromatography followed by cleavage of the modified dendroaspin from GST. Some products of the invention are made by producing an RGD-free dendroaspin as described above and chemically ligating a non-dendroaspin species to it. USE The peptides of the invention may be used for scientific investigations or, if pharmacologically active, may be used as pharmaceuticals. We have found that the dendroaspin molecule provides an excellent scaffold for carrying "foreign" sequences and presenting them to potential targets. In this respect, the small size and conformational stability of the dendroaspin scaffold make it a good model for experimental use as well as pharmaceutical use. Moreover, the fact that the sequence and conformation of dendroaspin are known enables amino acid sequences to be inserted in a position where it can be predicted that they will be exposed. A particular benefit of dendroaspin is that the RGD site is presented in a conformational environment which appears to improve association of the sequence at the RGD domain (RGD of course in wild type dendroaspin) with pockets in target structures as compared with linear peptides. Thus, the platelet-binding (GP Ilb/IIIa receptor-binding) activity of RGD in dendroaspin is about 1,000 times greater than that of RGD linear peptide. The molecules of the invention are particularly useful, therefore, for presenting amino acid sequences to receptors and other structures having pockets. Preferred polypeptides of the invention, therefore, have at the RGD domain a replacement ammo acid sequence having receptor-binding activity One class of polypeptides has at its RGD domain an ammo acid sequence which, in its native polypeptide, enters a pocket to function The dendroaspin framework is useful for presenting ammo acid sequences to targets for experimental purposes Thus, the polypeptides of the invention are useful for investigating the function, effects or activity of "foreign" test sequences, e.g for product development purposes In other words, the polypeptides of the invention are useful for the purpose of developing active agents, especially for pharmaceutical purposes or to obtain information useful in the development of small molecule therapeutic or diagnostic agents, for example Accordingly, the present invention further provides a method for testing the biological, pharmacological and/or biochemical activity of a candidate ammo acid sequence which method comprises incorporating the candidate sequence into a polypeptide according to the present invention Preferably, the method further comprises exposing the test polypeptide thereby produced to a receptor, 'pocket' or other interactive entity (whether in vivo or in vitro) and, optionally, measuring the binding thereto or interaction therewith. Optionally, the test sequence may also be exposed to the receptor or other interactive entity in the presence of a control substance (whose response, e.g. binding or interaction, in the absence of the test polypeptide is known) and the response of the test polypeptide and/or of the control substance thereafter measured. The present invention thereby provides a candidate ammo acid sequence, e.g. polypeptide, identifiable by the test method according to the invention, its use as identifiable, and pharmaceutical formulations thereof. The invention further provides a molecule comprising such a candidate polypeptide, especially the test polypeptide incorporated in a dendroaspin scaffold as defined hereinbefore and (the residue of) the candidate polypeptide The pharmacologically active polypeptides may be formulated as a pharmaceutical composition comprising a polypeptide as hereinbefore defined, optionally further comprising a pharmaceutically acceptable excipient or carrier A plurality of therapeutic polypeptides of the invention of different functionalities may be combined together in a pharmaceutically acceptable form so as to provide a desired treatment, and/or they may be combined with one or more other therapeutic or prophylactic agents. The therapeutic polypeptides of the invention are preferably formulated for intravenous injection or intravenous infusion although other methods of administration are possible, e.g oral, subcutaneous or intramuscular, should it be desired to provide a slow release into the circulatory system of an individual. Also possible is the formulation of the polypeptide for use with implanted controlled release devices such as those used to administer growth hormone, for example. One formulation may comprise extravasated blood combined with a polypeptide of the invention at a concentration in the range InM - 60μM This blood may be stored in ready to use form and provides an immediate and convenient supply of blood for transfusion in cases when clotting must be avoided such as during or immediately following surgical procedures. The invention includes a therapeutic polypeptide as hereinbefore defined for use in medicine, preferably as a pharmaceutical. The invention also provides for the use of a pharmacologically active polypeptide as hereinbefore defined for the manufacture of a medicament, which may for example be for the treatment or prophylaxis of disease associated with binding at a receptor or with thrombosis, more particularly thrombosis, myocardial infarction, retinal neovascularization, endothelial injury, dysregulated apoptosis, abnormal cell migration, leukocyte recruitment, immune system activation, tissue fibrosis and tumoπgenesis. The invention also provides methods for the treatment by therapy or prophylaxis of diseases associated with binding at a receptor or with thrombosis; more particularly thrombosis, myocardial infarction, retinal neovascularization, endothelial injury, dysregulated apoptosis, abnormal cell migration, leukocyte recruitment, immune system activation, tissue fibrosis and tumoπgenesis. The methods comprise administering a therapeutically effective amount of a polypeptide as hereinbefore defined. Brief Description of the Drawing Figure 1 comprises alignments of modified dendroaspins where the inserted ammo acid sequences are listed beneath the ammo acid sequence of dendroaspin EXAMPLE 1 KGD-Dendroaspin Materials— Restriction enzymes, T4 polynucleotide kinase, T4 DNA gase, IPTG (isopropyl-β- D-thio-galactopyranoside) and DH5α competent cells were purchased from Life Technologies Ltd (U.K.) or Promega Ltd. (Southampton, U.K.). Vent (exo-) DNA polymerase was supplied by New England Biolabs Ltd (Hitchin, U. K.) Protemase Factor Xa was purchased from Boehπnger Mannheim (Sussex, England). Human fibrinogen (grade L) was purchased from Kabi (Stockholm, Sweden). Lyophilised snake venoms were obtained from either Latoxan (05150 Rosans, France) or Sigma Chemical Ltd (Dorset, U. K.). Oligonucleotides were made by Cruachem Ltd., (Glasgow, U. K.) and further purified by denaturing PAGE on a 15% acrylamide/8 M urea gel. Deoxynucleotide triphosphates (dNTPs), dideoxynucleotide triphosphates (ddNTPs) and plasmid pGEX-3X, a vector that expresses a cloned gene as a fusion protein linked to glutathione S- transferase (GST), and Glutathione-Sepharose CL-4B were purchased from Pharmacia Biotech Ltd. (Herts, U. K.). "Geneclean" kit and Plasmid maxi Kit were purchased from Bio 101, La Jolla CA. U.S.A. and Qiagen Ltd., Surrey, U.K. respectively. The sequencing enzyme (Sequenase 2.0) was obtained from Cambridge Bioscience (Cambridge, U. K.). [ 35 S]dATP[αS] and 125 I (15.3 mCi / mg iodine) were supplied by NEN Dupont (Herts, U.K.) and Amersham International Pic (Amersham, Bucks, England), respectively. Construction of the expression vectors— A dendroaspin gene was constructed from synthetic oligonucleotides, using the same 10 oligonucleotides shown in Figure 2A of WO 98/42834. Each purified oligonucleotide was phosphorylated at 37 °C for 60 min in the presence of ImM ATP and T4 polynucleotide kinase. Each pair of overlapping phosphorylated oligonucleotides was annealed separately on a Perkin-Elmer/Cetus thermal cycler. The following programme was used: 95 °C 5 min, 70 °C 30s then slowly cooling to room temperature. Ligation was performed at 16 °C for 15 hours in a total volume of 50 μl containing approx. 1 nM of each annealed fragment, 50 mM Tris-HCI (pH 7.6), 10 imM MgCI 2 , 1 mM ATP and 5% PEG 8000 and 5 units of T4 DNA ligase. After ligation, the dendroaspin gene was amplified by PCR using 1 μl of ligation mixture as template with oligo 1 and 10 as primers and 2 units of Vent DNA polymerase. The following programme was applied: one cycle of 3 min at 94 °C and 1 min at 72 °C, followed by 39 cycles of 30s at 94 °C, and 2 min at 72 °C. The amplification product was checked and found to be of expected size (216 bp) as ascertained on a 2 % agarose gel and further purified on a 2 % low-melting-point agarose gel. The dendroaspin gene was digested with EcoRI and BamHI and then cloned into the restriction vector pGEX-3X to produce recombinant plasmid pGEX-Dendroaspin gene. The same protocol is followed in the construction of the non-wild type expression vectors, for example the pGEX-KGD-Dendroaspin gene (see below). The KGD-dendroaspin gene was produced by using a Transformer™ site-directed mutagenesis kit (Clontech Laboratories Inc, Palo Alto, California, USA). A selection oligonucleotide was designed to introduce a novel restriction site (BamHI→ ACC65I) into the PGEX-3X vector to allow selection of recombinant from parental constructs by digestion with ACC65I. After annealing, ligation and digestion, the reaction mixture was transformed into E coli mut S cells (Clontech) and subsequent colonies were screened by ACC65I restriction analysis. After two or three rounds of restriction with ACC65I and transformation, more than 90 % recombinant clones were identified. In the mutagenesis procedure, there were used the selection primer dGAAGGTCGTGGGTACCATATCGAAGGTCGT and the mutagenesis primer dTGCTTCACTCCGAAAGGTGACATGCCGGGTCCGTAC. Transformation and protein expression— Recombinant gene (5 ng) was used to transform 50 μl of £ cσ//DH5α competent cells by standard methods (34). The presence of correct coding sequence of the constructs was verified by complete DNA sequencing of the inserted fragments using the dideoxy chain-termination method (35). Bacterial culture conditions were carried out as follows: the culture was inoculated with an overnight seed culture (1%, v/v) and grown in LB/ampicillin medium (100 μg/ml) and shaken at 37 °C until it reached an Agoo of 0.7, then IPTG was added to a final concentration of 0.1 mM for induction. The cells were grown for an additional 4 hours at a lower temperature of 30 °C and harvested by centrifugation. Purification of native and recombinant snake venom RGD proteins— Elegantin, and dendroaspin were purified using reverse-phase HPLC as described previously (36). Recombinant dendroaspins were purified as follows: the cell pellets were suspended in PBS buffer (pH 7.4) containing 1% Triton X-100 and the protease inhibitors PMSF (1 DM), pepstatin (5 Dg/ml), aprotinin (5 μg/ml), trypsin inhibitor (1 μg/ml) , 1 mM EDTA , and sonicated on ice. The sonicated mixture was centrifuged at 7,800 x g at 4 °C to pellet the cell debris and insoluble material. Recombinant GST-dendroaspin and GST-mutant-dendroaspins from supernatants were purified by affinity chromatography on glutathione-Sepharose CL-4B columns by absorption in PBS containing 150 mM NaCI and elution with 50 mM Tris-HCI containing 10 mM reduced glutathione (pH 8.0). With the remaining insoluble fusion protein in the pellets, solubilisation was achieved in the presence of 8 M urea, by gently shaking at room temperature for 30 min and subsequent renaturation by continual dilution and dialysis at room temperature against Tris-HCI buffer. The refolded fusion protein mixture was subjected to further centrifugation and affinity-purification. The purification was monitored by SDS-PAGE and the appropriate fractions comprising the recombinant GST- Dendroaspin and GST-mutant-dendroaspins were digested in the presence of 150 mM NaCI, 1 mM CaCI 2 and Factor Xa (1:100, w/w Factor Xa : fusion protein) at 4 °C for 24 hours. After cleavage, the fractions were loaded onto a Vydac C i8 reverse phase HPLC analytical column (TP104) and eluted with a gradient of 0-26% acetonitrile (1.78% per min) containing 0.1 % trifluoroacetic acid (TFA), followed by 26-36% acetonitrile in 0.1% TFA (0.25% per min). When necessary, further analytical columns were run under the same conditions. The fractions from HPLC were freeze-dried, dissolved in water and assayed for the inhibition of ADP-induced platelet aggregation. Purified wild-type dendroaspin and mutants were characterised by 20% SDS-PAGE and electrospray ionisation mass spectrometry. Measurement of platelet aggregation— Platelet aggregation was measured by the increase in light transmission as described previously (36, 37). Briefly, platelet rich plasma (PRP) was prepared from citrated human blood, obtained from healthy individuals, by centrifugation at 200 x g for 15 min. Washed platelets were prepared from PRP and resuspended in adhesion/aggregation buffer (145 mM NaCI, 5 mM KCI, 1 mM MgCI 2 , 2 mM CaCI 2 , 10 mM 8 glucose, 3.5 mg/ml BSA and 10 mM HEPES, pH 7.35) and adjusted to a count of 3 x 10 /ml Platelet aggregation (320 μl incubations) was induced with 10 μM ADP in the presence of 1.67 mg/ml fibrinogen and measured using a Payton Dual-Aggregometer linked to a chart recorder KGD-dendroaspin was found to show potent inhibition of ADP-mduced platelet aggregation Measurement of platelet adhesion— Platelet adhesion is measured as described previously (37) Briefly, 96 well plates are coated overnight at 4 °C with either human fibrinogen or fibronectin reconstituted in phosphate buffered saline (PBS) (pH 7.4) at appropriate concentrations (2-10 μg/ml, 100 μl) Platelets are treated with antagonists at appropriate concentrations for 3 mm before the addition (90 μl) to the microtitre plates which are pre-loaded with 10 μl of 500 μM ADP (final cone. 50 μM) and the number of adherent platelets is determined by measurement of endogenous acid phosphatase using 130 μl/well of the developing buffer (sodium acetate, pH 5.5, 10 mM >nιtrophenyl phosphate, 0.1% Triton X- 100) and read at 410/630 nm on an automated plate reader Iodination of Ligands and Ligand Binding Studies— Iodmation of all proteins used in this study is performed using Enzymobead Radioiod ation Reagent (Biorad Laboratories) according to the manufacturer's specifications. The binding of 125 I-labelled disintegπns, dendroaspin and mutant dendroaspins to washed platelets is performed under equilibrium conditions essentially as described previously (37). Briefly, the incubation mixture is composed of 300 μl of washed platelets (3 x 10 8 /ml), 10 μl of agonist (1.75 mM ADP giving a final cone. of 50 μM), 10 μl of 125 I-labelled protein samples, 5-20 μl resuspension buffer and made to a final volume of 350 μl. In antibody inhibition studies, platelet suspensions are treated with antibody for 30 mm prior to exposure to ADP and then added to 125 I-proteιn samples and the mixture incubated at room temperature for a further 60 mm. Incubations are terminated by loading onto a 25% (w/v) sucrose, 1% BSA cushion and centrifugation at 12,000 x g for 10 mm. Both platelet pellets and supernatants are counted to determine the levels of bound and free ligand. Background binding levels are determined in the presence of a 50-fold excess of cold disintegrin or 10 mM EDTA. Expression and purification of recombinant wild-type dendroaspin and mutant- dendroaspins— The synthetic wild-type and mutated dendroaspin genes were cloned into the expression vector pGEX-3X at the carboxyl terminus of the glutathione S-transferase (GST) gene with a Factor Xa cleavage sequence positioned 5' of the gene coding for these recombinant proteins. The expression of the GST-fusion protein in £ coli was induced by addition of IPTG to the growth medium, as described under the headings "Construction of the expression vector" and "Transformation and protein expression" In contrast to non-induced transformants, analysis of IPTG treated cell lysates by SDS-PAGE showed an emergence of a 32 kDa protein corresponding to the GST-fusion protein The GST-protein was purified by affinity chromatography on glutathione-Sepharose CL-4B column and monitored by SDS-PAGE Elution of the absorbed material with glutathione resulted in the appearance of a major band migrating at 32 kDa and a minor band at 28 kDa in 12.5% polyacrylamide gels. This minor 28 kDa component may correspond to free GST released from the GST-protein by an endogenous bacterial protease with Factor Xa-like activity since the relative levels of this species varied with different preparations. Treatment of the purified GST-proteins with Factor Xa released recombinant proteins migrating as 7 kDa bands, approximating the size of dendroaspin, and free GST appearing as an intensification of the 28 kDa band identified by SDS-PAGE. The 7 kDa protein was further purified to homogeneity by reverse-phase HPLC with the active fraction identified by testing aliquots from each peak for their ability to inhibit ADP-induced platelet aggregation in PRP. Further characterisation by mass spectrometry confirmed the successful cleavage at Arg 1 by Factor Xa protease treatment. Modified Molecules- Figure 1 shows the sequences of modified monofunctional and bifunctional dendroaspins obtainable by mutagenesis of the dendroaspin gene as described in the specification and in WO 98/42834. The sequences of these molecules are shown in the sequence listing. EXAMPLE 2 KQAGDV-Dendroaspin The same procedures as described in Example 1 were followed to express and purify KQAGDV- dendroaspin. The mutagenesis primer used in the site-directed mutagenesis was: dGGT TGC TTC ACT CCG AAA CAG GCT GGT GAC GTT CCG GGT CCG TAC TGC, corresponding to the amino acid sequence: GCFTPKQAGDVPGPYC. It will be appreciated from the aforegoing that the invention provides the use of dendroaspin as a scaffold for one or more non-dendroaspin amino acid sequences in a dendroaspin framework in which the native RGD motif has been deleted or has been replaced by (i) an amino acid sequence having no integrin-binding activity or (ii) an aspartic acid- or glutamic acid-containing integrin-binding amino acid sequence other than RGD. REFERENCES 1. Kieffer, N., and Phillips, D. R. (1990) Ann. Rev. Cell Biol. 6, 329-357 2. Hynes, R. 0. (1992) Cel/69, 11-25 3. McEver, R. P. (1992) Curr. Opin. Cell Biol. 4, 840-849 4. Smyth, S. S., Joneckis, C. C, and Parise, L. V. (1993) BloodSl, 2827-2843 5. Giancotti, F. G. and Mainiero, F. (1994) Biochim. Biophys. Ada. 1198, 47-64 6. Pierschbacher, M. 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Claims: CLAIMS 1 A product comprising a dendroaspin scaffold in which the native RGD motif has been deleted or has been replaced by a replacement ammo acid sequence which is (i) an ammo acid sequence having no integπn-binding activity or (n) an integrin-binding ammo acid sequence and comprising a tripeptide sequence other than RGD containing D or E adjacent to G 2 A product of claim 1 in which the tripeptide sequence is of the formula B-J-Z wherein I) J-Z is GD or GE and B is R, K, Q, A, H, N, A, V, I, L, M, F, P or W; II) B-J is DG or EG and Z is any ammo acid; or III) J is D or E and B and Z are each independently selected from A, V, I, L, M, F, P or W. 3. A products of claim 2(1) in which J-Z is GD. 4. A products of claim 2(1) or claim 4 in which B is R, K, Q, A, H or N, provided that B-J-Z 5. A product of claim 4 in which B is R, K, Q or A. 6. A product of any of claims 2(1) and 3 to 5 in which B-J-Z is bonded at its C-terminal end to M, W, N or V. 7 A product of claim 6 in which said M, W, N or V residue is followed by the P which is at position 47 of wild type dendroaspin or by an A residue substituted therefor. 8. A product of any of claims 2(1) and 3 to 7 in which the integrin-binding ammo acid sequence is preceded by the P which is at position 42 of wild type dendroaspin or by an A residue substituted therefor. 9. A product of claim 2(1) or 3 in which B is A, V, I, M, F, P, W. 10 A product of claim 9 in which B is L or V 11 A product of claim 10 in which B is L and is preceded by M. 12 A product of claim 2(11) in which B-J is DG 13. A product of claims 2(11) or claιml2 in which Z is E, R or P. 14. A product of any of claims 2(11), 12 and 13 in which Z is followed by the P which is at position 47 of wild type dendroaspin or by an A inserted before the wild type position 47 P. 15 A product of claim 2 (III) in which J is D. 16. A product of claim 2(111) in which B-J-Z is LDV. 17. A product of any of claims 2(111), 15 and 16 in which B-J-Z is preceded by an I residue. 18. A product of claim 1 which comprises a said replacement ammo acid sequence (i) having no integrin binding activity, the replacement ammo acid sequence having a receptor- binding function. 19. A product of claim 1 which comprises a said replacement ammo acid sequence (i) having no integrin binding activity, the replacement ammo acid sequence being one which in its native polypeptide enters a pocket to function. 20. A product of any of claims 1 to 19 which, in addition to deletion or replacement of the RGD motif, comprises at least one foreign (non-wild-type dendroaspin) domain. 21. A product of claim 20, wherein the at least one non-wild-type dendroaspin domain comprises at least one non-dendroaspm domain which confers functionality on the product. 22. A product of claim 20 or claim 21, comprising at least two said non-wild-type dendroaspin domains, the non-wild-type dendroaspin domains optionally having the same sequence. 23. A product of any of claims 20 to 22 wherein said at least one non-wild-type dendroaspin domain comprises a said domain having two or more ammo acid sequence portions separated by at least one ammo acid residue of dendroaspin 24 A product of any of claims 20 to 23 which contains a said non-wild-type dendroaspin domain conferring platelet derived growth factor (PDGF) activity, glycoprotein IBα activity, hirudin activity, thrombomodulin activity, vascular epidermal growth factor activity, transforming growth factor-βl activity, basic fibroblast growth factor activity, angiotensin II activity, factor VIII activity, von Willebrand factor activity, tick anticoagulant protein (TAP) activity or nematode anticoagulant protein (NAP) activity 25 A product of claim 24, wherein the non-wild-type dendroaspin domain is a sequence derived from platelet derived growth factor (PDGF), glycoprotein IBα, hirudin, thrombomodulin, vascular epidermal growth factor, transforming growth factor-βl, basic fibroblast growth factor, angiotensin II, factor VIII, von Willebrand factor, tick anticoagulant protein (TAP) or nematode anticoagulant protein (NAP), or a sequence having homology to at least part of such sequence. 26. A product of any of claims 20 to 25, wherein the non-wild-type domains is/are incorporated into (a) loop I and/or loop II; (b) loop I and/or loop III; (c) loop II and/or loop III, or loop I, loop II and loop III of the dendroaspin scaffold. 27. A product of claim 26, wherein there is a single said non-wild-type domain and the domain is incorporated into either loop I or loop II. 28. A product of any of claims 20 to 25, wherein the non-wild-type domains is/are contained in the dendroaspin scaffold between ammo acid residues selected from one or more of 4-16, 18-21 or 23-36, or at the end of the dendroaspin scaffold after residue 50 29. A product of claim 28, in which there is a single non-wild-type domain. 30. A product of any of claims 20 to 25 which is a polypeptide which comprises a dendroaspin scaffold in which the RGD motif has been replaced by a said integrin-binding ammo acid sequence at one domain and a non-dendroaspin species which confers a second functionality on another domain. 31. A product of claim 30 in which the residues of a non-loop region of the dendroaspin scaffold are augmented by the non-dendroaspin species by ligating the latter directly or through a linker to a terminal sequence of the dendroaspin scaffold. 32. A product of any preceding claim, wherein loop III is additionally modified as compared with native dendroaspin by insertion, deletion or substitution of one or more am o acid residues 33. A product of claim 32 wherein a maximum of 8 and a minimum of 1 ammo acids are modified by said additional modification within loop III. 34. A product of claim 32 or claim 33, wherein RGD has been replaced by a said integrin binding sequence and said additional modification comprises modification of the ammo acids flanking said integrin binding sequence 35. A product of any preceding claim, wherein loop I and/or loop II are additionally modified by insertion, deletion or substitution of one or more ammo acid residues 36. A product of any preceding claim, which contains not more than 100 ammo acid residues more than native dendroaspin. 37. A product of claim 36, which contains from 14 to 36 ammo acid residues more than native dendroaspin. 38. A nucleic acid molecule encoding a polypeptide product of any one of claims 1 to 37. 39. A nucleic acid of claim 38, operatively linked to a promoter and optionally to a nucleic acid sequence encoding a heterologous protein or peptide thereby to encode a fusion product. 40. A nucleic acid of claim 39, wherein the promoter is IPTG induαble and optionally the heterologous protein or peptide is glutathione S-transferase. 41. A plasmid comprising a nucleic acid of any one of claims 38 to 40 42. Plasmid pGEX-3X comprising a nucleic acid of claim 38. 43. A host cell transformed with a plasmid of claim 41 or claim 42 44 A host cell of claim 43 which is E coli. 45 A cell culture comprising host cells of claim 43 or claim 44 46. A method of producing a polypeptide as defined in any of claims 1 to 37 comprising cultuπng a host cell of claim 43 or claim 44 so as to express said polypeptide, extracting the polypeptide from the culture and purifying it 47 A method of producing a polypeptide comprising a dendroaspin scaffold, the method comprising: a) preparing an expression vector comprising a nucleic acid sequence encoding a dendroaspin scaffold of claim 1 operatively linked to a promoter and optionally linked to a nucleic acid sequence encoding a heterologous protein for co-expression therewith; and b) transforming a host cell with the vector and causing the host cell to express the modified dendroaspin nucleic acid sequence. 48. A method of claim 47, wherein step (a) comprises a) (i) assembling from overlapping oligonucleotides the coding sequence of a dendroaspin scaffold containing an RGD motif and operatively linking the resulting cDNA to a promoter, the promoter optionally being linked to a nucleic acid sequence encoding a heterologous protein for expression of fusion protein; and a) (ii) modifying the RGD-encodmg domain of the expression vector to encode a dendroaspin scaffold in which RGD has been deleted or replaced by a replacement ammo acid sequence as defined in any of claims 1 to 14. 49 A method of claim 48, in which step (a) (n) further comprises, before or after said modification, modifying at least one other domain of the nucleic acid sequence of the vector encoding the dendroaspin scaffold by one or more of the insertion, deletion or substitution of nucleic acid residues so that on expression the dendroaspin scaffold comprises a corresponding domain having a non-wild-type dendroaspin sequence. 50 A method of claim 47, wherein step (a) comprises constructing from oligonucleotides an expression vector comprising a nucleic acid sequence encoding a dendroaspin sequence in which the RGD-encodmg domain has been deleted or replaced by a replacement am o acid sequence as defined in any of claims 1 to 14 and, optionally, modifying at least one other domain of the nucleic acid sequence of the vector encoding the dendroaspin scaffold by one or more of insertion, deletion or substitution of nucleic acid residues so that on expression the dendroaspin scaffold comprises a corresponding domain having a non-wild-type dendroaspin sequence. 51. A method of any of claims 46 to 50, further comprising the steps of. d) extracting the modified dendroaspin from a host cell culture, e) purifying the modified dendroaspin from the cell culture extract, and, if the modified dendroaspin is a fusion protein, cleaving the dendroaspin portion from the heterologous portion of the fusion protein 52. A method of claim 51 wherein the heterologous protein is glutathione S-transferase (GST) and the purification involves GST affinity chromatography followed by cleavage of the modified dendroaspin from GST. 53. A polypeptide product of any of claims 1 to 37 obtainable by the method of any one of claims 46 to 52. 54. A pharmaceutical composition comprising a pharmacologically active product of any one of claims 1 to 37 or 53. 55. A composition as claimed in claim 54, further comprising a pharmaceutically acceptable excipient or carrier. 56. A pharmacologically active product as claimed in any one of claims 1 to 37 or 53 for use as a pharmaceutical. 57. The use of a pharmacologically active product as claimed in any one of claims 1 to 37 or 53 for the manufacture of a medicament for the treatment or prophylaxis of disease associated with thrombosis. 58. The use as claimed in claim 57, wherein said disease is one of more of thrombosis, myocardial infarction, retinal neovascularization and endothelial injury 59 A method for the treatment or prophylaxis of a disease associated with thrombosis in a human or animal patient, comprising administering to the patient an effective amount of a pharmacologically active product as claimed in any one of claims 1 to 37 or 53 60. The use of a product as claimed in any one of claims 1 to 37 or 53 to investigate the function, effects or activity of one or more non-wild-type dendroaspin sequences contained in the product. 61 A method of investigating the function, effects or activity of a species other than a wild- type dendroaspin sequence, comprising providing a product of any of claims 1 to 37 or 53 which comprises said species and performing in vivo or in vitro tests with said product 62. A method of claim 61, which further comprises formulating into a medicament a product containing a species whose functions, effects or activity were investigated by carrying out the method of claim 61. 63 The use of dendroaspin as a scaffold for one or more non-dendroaspm ammo acid sequences in a dendroaspin framework in which the native RGD motif has been deleted or has been replaced by (i) an am o acid sequence having no integrin-binding activity or (n) an aspartic acid- or glutamic acid-containing integrin-binding ammo acid sequence other than RGD

Inventors: KAKKAR VIJAY VIR, LU XINJIE, KAKKAR, VIJAY, VIR, LU, XINJIE
Applicants: TRIGEN LTD, TRIGEN LIMITED
Application year: 2001
Main classification: C12N15
IPC codes: A61K38, A61K45, A61P7, A61P9, C07K14, C12N1, C12N15, C12P21, C12R1