Abstract:
Methods are disclosed for the production and purification of hydrophobic fusion proteins production and purification of said hydrophobic polypeptides, proteins or peptides. Homogeneous monomeric β-amyloid peptide and tests for screening amyloid toxicity-inhibiting drugs using this monomeric β-amyloid peptide relate to these fusion proteins.

Description:
FIELD OF THE INVENTION 
     The subject invention relates to a process for producing hydrophobic polypeptides, proteins and peptides, and fusion proteins for use in producing same. 
     BACKGROUND OF THE INVENTION 
     The ability to prepare hybrid genes by gene technology opens up new routes for working-up recombinant proteins. By linking the coding gene sequence of a desired protein with the coding gene sequence of a protein fragment having a high affinity for a ligand (affinity peptide), it is possible to produce a fusion protein and purify a desired recombinant protein in the form of the fusion protein in one step through the use of the affinity peptide. By site-directed mutagenesis, it is also possible to introduce specific chemical or enzymatic cleavage sites at the point of linkage of the affinity peptide and the desired recombinant protein, so that after purification of the fusion protein by means of a suitable affinity resin, the desired recombinant protein can be recovered by chemical or enzymatic cleavage. 
     However, recovering the desired recombinant protein may turn out to be extremely difficult when the desired recombinant protein also contains such chemical or enzymatic cleavage sites in its amino acid sequence. In such cases, the desired recombinant protein ends up being rapidly degraded. 
     In order to inhibit this degradation, the present invention provides fusion proteins and processes which allow selective cleavage at a specific chemical or enzymatic cleavage site without affecting the desired recombinant protein. Methods of the present invention are specifically applicable for production of hydrophobic polypeptides, proteins or peptides. 
     SUMMARY OF THE INVENTION 
     The present invention is concerned with fusion proteins of the formula: 
     
         A--B--C 
    
     wherein A is a bulky hydrophilic peptide, B is a selective cleavage site, and C is a desired hydrophobic polypeptide, protein or peptide. 
     The term &#34;bulky hydrophilic peptide&#34; is used in connection with fusion proteins in accordance with the invention and relates to hydrophilic peptides which are characterized by their size and the content of hydrophilic amino acids giving rise to a well structured domain. 
     The bulky hydrophilic peptide A of the fusion proteins in accordance with the invention serves a dual function: (a) to facilitate high expression of the fusion proteins, and (b) to expose cleavage site B to the mobile phase on a hydrophobic matrix column. Preferred bulky hydrophilic peptides of the fusion proteins in accordance with the invention are those with the peptide sequence of the formula 
     
         (NANP)x 
    
     wherein x is 10-40, with 19 being most preferred. 
     Selective cleavage sites include chemical and enzymatic cleavage sites. 
     Suitable selective enzymatic cleavage sites include (i) the amino acid sequences -(Asp) n  -Lys-, wherein n signifies 2, 3 or 4, or -Ile-Glu-Gly-Arg- which can be specifically recognized by the proteases enterokinase and coagulation factor X a , respectively, (ii) an arginine residue or a lysine residue cleaved by trypsin, (iii) a lysine residue cleaved by lysyl endopeptidase, and (iv) a glutamine residue cleaved by V8 protease. 
     Suitable selective chemical cleavage sites include (i) tryptophan residues cleaved by 3-bromo-3-methyl-2-(2-nitrophenylmercapto)-3H-indole, (ii) cystein residues cleaved by 2-nitroso-5-thiocyano benzoic acid, (iii) the amino acid dipeptides Asp-Pro or Asn-Gly which can be cleaved by acid and hydroxylamine, respectively, and preferably, (iv) a methionine residue which is specifically cleaved by cyanogen bromide (CNBr). 
     The term &#34;hydrophobic polypeptide, protein or peptide&#34; is used in connection with the fusion proteins in accordance with the invention and relates to hydrophobic polypeptides, proteins or peptides which elute from reverse phase HPLC columns at concentrations between about 30% and about 60%, preferably around about 40% organic solvent in aqueous buffer, e.g. at a concentration of higher than about 40% ethanol in aqueous buffer. 
     Hydrophobic polypeptides, proteins or peptides include, for example, surface antigens, lymphokine receptors, HIV-1 and HIV-2 envelope and structure proteins, hepatitis C envelope and structure proteins, and any peptide with membrane anchor sequences. Preferred hydrophobic polypeptides, proteins or peptides are β-amyloid peptide (bA4-amyloid) having the sequence: 
     
         1                                                          42 
    
     
         DAEFRHDSGYEVHHQKLVFFAEDVGSNKGAIIGLMVGGVVIA (Seq ID No: 1) 
    
     point mutations of bA4-peptide having at position 35 a leucine (Seq ID No:3), serine (Seq ID No:4), glutamine (Seq ID No:5) or glutamic acid (Seq ID No:6) residue instead of a methionine or methionine sulfoxide residue and HIV-1 envelope peptide having the sequence: 
     
         1                                                          35 
    
     
         RILAVERYLKDQQLLGIWGCSGKLICTTAVPWNAS (Seq ID No: 11) 
    
     Bulky hydrophilic peptides and the selective cleavage sites of fusion proteins in accordance with the invention can be linked either to the amino terminal amino acid or to the carboxy terminal amino acid of the hydrophobic polypeptide, protein or peptide. 
     The fusion proteins in accordance with the present invention can optionally contain specific sequences that preferably bind to an affinity carrier material. Examples of such sequences are sequences containing at least two adjacent histidine residues (see in this respect European Patent Application Publication No. 282 042 corresponding to U.S. Pat. Nos. 5,284,933 and 5,310,663, the contents of each being herein incorporated by reference). Such sequences bind selectively to nitrilotriacetic acid nickel chelate resins (Hochuli and Dobeli, Biol.Chem. Hoppe-Seyler 368, 748 (1987); European Patent No. 253 303, corresponding to U.S. Pat. Nos. 4,877,830 and 5,047,513, the contents of each being herein incorporated by reference). Fusion proteins of the present invention which contain such a specific sequence can, therefore, be separated selectively from remaining polypeptides. The specific sequence can be linked either to the amino acid sequence of the bulky hydrophilic peptide or the amino acid sequence of the hydrophobic polypeptide, protein or peptide. 
     The present invention is also concerned with genes which code for these fusion proteins, expression vectors which contain these genes, microorganisms transformed with these expression vectors as well as a process for the preparation of said genes, expression vectors and transformed microorganisms. 
     Preparation of the fusion proteins in accordance with the invention can be effected according to methods of recombinant DNA technology described in the literature. Preferably, a nucleotide sequence coding for the desired hydrophobic polypeptide, protein or peptide is firstly synthesized and this is then linked with a nucleotide sequence coding for the bulky hydrophilic peptide and the selective cleavage site. 
     Incorporation of the thus-obtained hybrid gene into expression vectors can be effected using methods known to the skilled artisan. In this context, reference can be made to the textbooks of Maniatis et al. (&#34;Molecular Cloning&#34;, Cold Spring Harbor Laboratory, 1982) and Sambrook et al. (&#34;Molecular Cloning-A Laboratory Manual&#34;, 2nd. ed., Cold Spring Harbor Laboratory, 1989), the contents of both being herein incorporated by reference. 
     Methods for the expression of fusion proteins in accordance with the invention are also known to the skilled artisan, and are described in detail in the aforementioned textbooks. They embrace the following procedures: 
     a) transformation of a suitable host organism, advantageously E. coli, with an expression vector in which an aforementioned hybrid gene is operatively bonded to an expression control sequence; 
     b) cultivation of the thus-obtained host organism under suitable growth conditions; and 
     c) extraction and isolation of the desired fusion protein from the host organism. 
     Host organisms include gram-negative and gram-positive bacteria, for example E. coli and B. subtilis strains. E. coli strain M15 is an especially preferred host organism of the present invention. Apart from the above-mentioned E. coli strain there can, however, also be used other generally accessible E. coli strains, for example E. coli 294 (ATCC No.3144), E. coli RR1 (ATCC No.31343) and E. coli W3110 (ATCC No. 27325). 
     Fusion proteins in accordance with the present invention allow selective cleavage at a specific chemical or enzymatic cleavage site without affecting the desired hydrophobic polypeptide, protein or peptide. Diffusion of the desired hydrophobic polypeptide, protein or peptide into the solid phase of a hydrophobic matrix column enables orientation of the fusion proteins in accordance with the present invention so as to hide the desired hydrophobic polypeptide, protein or peptide. The bulky hydrophilic peptide, on the other hand, exposes the selective cleavage site to the mobile aqueous phase. This allows for removal of the bulky hydrophilic peptide by selective cleavage, leaving only the desired hydrophobic polypeptide, protein or peptide bound to the column. The desired hydrophobic polypeptide, protein or peptide can then be eluted by addition of organic solvents. 
     Hence, the present invention also provides a process for the production and purification of a desired hydrophobic polypeptide protein or peptide, which process comprises the steps of: 
     a) passing an aqueous solution containing a fusion protein in accordance with the present invention through a hydrophobic matrix column, 
     b) flushing the column with a solution containing a cleavage reagent or an enzyme, and 
     c) removing the resulting desired hydrophobic polypeptide, protein or peptide with an aqueous water miscible solvent. 
     Hydrophobic matrix columns include cyanopropyl, cyclohexyl, phenyl, octyl or octadecyl group bonded silica matrix columns. In the preferred practice of the invention, RP - 18 (octadecyl bound silica microparticle column) under reverse phase high performance liquid chromatography (HPLC) conditions is used. 
     Prior to the loading with the inventive fusion protein, the hydrophobic matrix column is conveniently equilibrated with an aqueous buffer. The equilibration buffer may contain a denaturing agent or a chaotropic agent, for example guanidine-HCl, urea or a detergent, e.g. TRITON. Addition of such a denaturing agent, chaotropic agent or detergent permits problem-free operation even with the subject fusion proteins which tend to be extremely difficult to solubilize in aqueous solution. 
     The fusion protein in accordance with the present invention may be applied onto a hydrophobic matrix column in aqueous buffer which may also contain a denaturing agent or a detergent, for example guanidine-HCl, urea or TRITON. 
     Cleavage is performed by flushing the column with an aqueous buffer containing a cleavage reagent or an enzyme. Optimal buffer composition depends on the cleavage reagent or enzyme used and is conveniently determined on a case-by-case basis. 
     Elution of the desired hydrophobic polypeptides, proteins or peptides may be carried out using a gradient of an aqueous water miscible solvent. Suitable water miscible solvents for this purpose include alkanols, such as n-propanol, 2-propanol, ethanol, methanol, tert- butanol, or cyclic ethers, such as dioxane. Optimal elution conditions depend on desired hydrophobic polypeptide, protein or peptide to be purified, hydrophobic matrix, column dimensions etc., and are conveniently determined on a case-by-case basis. 
     The aforementioned process for production and purification of a desired hydrophobic polypeptide protein or peptide may also be carried out batchwise. The fusion protein in accordance with the present invention is then absorbed to a hydrophobic matrix in aqueous buffer. Cleavage is performed by incubating the hydrophobic matrix with an aqueous buffer containing the cleavage reagent or the enzyme. The desired hydrophobic polypeptide can be obtained by incubating the hydrophobic matrix with the aqueous water miscible solvent after removal of the cleavage reagent or enzyme and the bulky hydrophilic peptides. 
     In a preferred specific embodiment of the present invention, a novel process allowing production and purification of a desired hydrophobic polypeptide, protein or peptide is employed to purify β-amyloid peptides in monomeric form to homogeneity. 
     The specific process for producing a monomeric β-amyloid peptide as homogeneous peptide comprises the following steps in combination: 
     a) passing an aqueous solution containing a fusion protein in accordance with the present invention, wherein the desired hydrophobic peptide is the β-amyloid peptide, through a hydrophobic matrix column, 
     b) flushing the column with a solution containing a cleavage reagent or an enzyme, 
     c) obtaining monomeric β-amyloid peptide by elution with an aqueous water miscible solvent, 
     d) diluting the monomeric β-amyloid peptide with distilled water followed by lyophilization, and 
     e) optionally, if desired, purifying the monomeric β-amyloid peptide after lyophilization to achieve ultimate homogeneity. 
     In performing the specific process for producing monomeric β-amyloid peptide as a homogeneous peptide, the solution containing the fusion protein (wherein the desired hydrophobic peptide is a β-amyloid peptide, preferably in aqueous buffer containing a denaturing agent, e.g. guanidine-HCl or urea), is passed through the hydrophobic matrix column. In the preferred practice, RP-18 (octadecyl bound silica micro-particle column) under reverse phase high performance liquid chromatography (HPLC) conditions is used. Further suitable columns for this purpose include cyanopropyl, cyclohexyl, phenyl or octyl-columns (Bead size from about 5-30 mm). These columns are commercely, available from Vydac or Macherey-Nagel under the trademarks VYDAC or NUCLEOSIL. Cleavage is performed by flushing the column with an aqueous buffer containing a cleavage reagent or an enzyme. In the preferred practice, cleavage is performed by flushing the column with cyanogen bromide in an aqueous buffered water miscible solvent. The elution of the monomeric β-amyloid peptide is carried out using a gradient of an aqueous water miscible solvent, preferably an ethanol gradient. The monomeric β-amyloid peptide is immediately diluted with distilled water, e.g., by dropping the eluate into a container containing water, and is then lyophilized. If desired, the monomeric β-amyloid peptide may be purified by known methods, e.g. by preparative gel electrophoresis or by size exclusion chromatography, after lyophilization in order to achieve ultimate homogeneity. In the preferred practice preparative non-denaturing gel electrophoresis (for the isolation of large quantities of monomeric β-amyloid peptide) and gel filtration under HPLC conditions (for the isolation of small quantities of monomeric β-amyloid peptide) is applied. 
     The present invention also relates to the pure and homogeneous, toxic monomeric β-amyloid peptides obtained by the novel process. 
     The β-amyloid peptides in accordance with the present invention may be used for screening Alzheimer drugs. 
     The novel process allowing production and purification of a desired hydrophobic polypeptide, protein or peptide is also employed to purify HIV-1 envelope peptide Seq ID No: 11 to homogeneity using analogous conditions as those used for the purification of monomeric β-amyloid peptide (Example 7). 
     The HIV-1 envelope peptide Seq ID No: 11 obtained by the novel process may be used in diagnosing HIV infections. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The invention has been described in general terms hereinabove. The following Examples are intended to illustrate details of the invention, without thereby it in any manner. The following Examples can be understood better when read in conjunction with the accompanying Figures. The following symbols appear in these Figures: 
     `N25OPSN25OP29` represents the regulatable promoter/operator element N25OPSN25OP29, `RBSII` represents the synthetic ribosomal binding site RBSII; ` His!6`, ` NANP!19` and `amy` represent the genes encoding the 6xHis-NANP-amyloid fusion proteins of this invention; `bla`, `cat`, `lacI` and `neo` represent the genes for beta-lactamase, chloramphenicol acetyltransferase, lac repressor and neomycin phosphotransferase, respectively; `to`, `TE` and `T1` represent transcriptional terminators t o  of phage lambda, TE of phage T7 and T1 of the E. coli rrnB operon; `repl.` represents the replication regions of plasmids pBR322 and pREP4. 
     FIG. 1--A schematic drawing of the plasmid pREP4. 
     FIG. 2--A schematic drawing of the plasmid p6xHis-NANP-Met-Amy. 
     FIG. 3--A sequence listing displaying that part of the nucleotide sequence of plasmid p6xHis-NANP-Met-Amy (Seq ID No: 7) which encodes fusion protein 6xHis-NANP-Met-Amy (Seq ID No: 8). In this sequence, recognition sequences of some of the restriction enzymes depicted in FIG. 2 are indicated. The amino acid sequence represents in three-letter code the sequence of fusion protein 6xHis-NANP-Met-Amy, amino acids corresponding to the bA4-peptide are numbered. 
     FIG. 4--A schematic drawing of plasmid pB/E1-6xHis-NANP-Met-huAmy. 
     FIG. 5--A sequence listing displaying that part of nucleotide sequence of plasmid pB/E1-6xHis-NANP-Met-huAmy (Seq ID No: 9) which encodes fusion protein 6xHis-NANP-Met-huAmy (Seq ID No: 10). In this sequence, recognition sequences of some of the restriction enzymes depicted in FIG. 4 are indicated. The amino acid sequence represents in the three-letter code the sequence of fusion protein 6xHis-NANP-Met-huAmy, amino acids corresponding to the bA4-peptide are numbered. The lower part of FIG. 5 displays nucleotide sequences and encoded amino acids by which plasmid pB/E1-6xHis-NANP-Met-huAmy M35E!, which encodes fusion protein 6xHis-NANP-Met-huAmy M35E!, plasmid pB/E1-6xHis-NANP-Met-huAmy M35L!, which encodes fusion protein 6xHis-NANP-Met-huAmy M35L!, plasmid pB/E1-6xHis-NANP-Met-huAmy M35Q!, which encodes fusion protein 6xHis-NANP-Met-huAmy M35Q!, and plasmid pB/E1-6xHis-NANP-Met-huAmy M35S!, which encodes fusion protein 6xHis-NANP-Met-huAmy M35S!, differ from plasmid pB/E1-6xis-NANP-Met-huAmy. 
     FIGS. 6A and 6B--Illustrate bA4 analysis by non-denaturing agarose gel electropheresis. Analysis was performed with &#34;Serum Protein Electrophoresis system Paragon&#34; from Beckman according to the recommendations of the supplier. 8 μg (in 2 μl H 2  O) of peptide each were applied. Staining was with Coomassie brilliant blue for 3 h and destaining with 10% acetic acid, 45% methanol and 45% water. Samples were prepared in distilled water immediately before the experiment (f) or allowed to age for 2 days (a). The samples tested are given in the list below. 
     
         ______________________________________FIG. 6A (gel a)   FIG. 6B (gel b)______________________________________lane 1  human bA4 wash 1 f                 lane 1   M35S bA4 wash 1 flane 2  human bA4 wash 2 f                 lane 2   M35S bA4 wash 2 flane 3  human bA4 wash 3 f                 lane 3   M35S bA4 wash 3 flane 4  human bA4 wash 4 f                 lane 4   M35S bA4 wash 4 flane 5  human bA4 wash 4 a                 lane 5   M35S bA4 wash 4 alane 6  Standard BSA 2 mg                 lane 6   Standard BSA 10 mglane 7  M35L bA4 wash 1 f                 lane 7   M35Q bA4 wash 1 flane 8  M35L bA4 wash 2 f                 lane 8   M35Q bA4 wash 2 flane 9  M35L bA4 wash 3 f                 lane 9   M35Q bA4 wash 3 flane 10 M35L bA4 wash 3 a                 lane 10  rat bA4______________________________________ 
    
     FIG. 6C--Illustrates (gel c) the results of a comparison of the point mutants M35Q bA4 and M35E bA4. Point mutant M35E bA4 contains an extra negative charge which results in a higher mobility on the Beckman gel (lane 8: M35E bA4; lane 9: M35Q bA4). When M35E bA4 is mixed with M35Q bA4 after cleavage (lane 1) or when the fusion protein containing M35Q bA4 is mixed with the fusion protein containing M35E bA4 and cleaved according to the process of the present invention (lanes 3, 4, 5 and 6 (wash 1, 2, 3 and 4)) a clear separation is observed indicating the presence of monomeric bA4. 
     FIG. 7--Illustrates the results of bA4 chromatography on a size-exclusion column. 
     Fractions of 250 ml each were collected and analyzed by non-denaturing electrophoresis. Lane 1: bA4 applied onto the column. Lanes 2 to 10: peak fractions. 
     The marker proteins used to determine the size of bA4 were: 
     serum albumin (MW=65000; retention time=19.89 min), 
     ovalbumine (MW=45000; retention time=20.10 min), 
     lactalbumin (MW=14200; retention time=21.43 min) and 
     insulin (MW=5734; retention time=21.68 min). 
     The retention time of 22.54 min. points to a monomer with a MW of about 4500 daltons. This is in agreement with light-scattering data and ultracentrifugation experiments by the Yphantis method (D. A. Yphantis, Annals of the N.Y. Acad.Sci. 88, 586-601  1960!, the contents of which are herein incorporated by reference). 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The subject invention will now be described in terms of its preferred embodiments. These embodiments are set forth to aid in the understanding of the invention, but are not to be construed as limiting. 
     EXAMPLE 1 
     Expression Plasmid Used For the Preparation of the Fusion Protein 6xHis-NANP-Met-Amy 
     The expression plasmid p6xHis-NANP-Met-Amy (see FIGS. 2 and 3) was used for the preparation of the fusion protein 6xHis-NANP-Met-Amy. E. coli M15 cells transformed with plasmids pREP4 and p6xHis-NANP-Met-Amy were deposited in accordance with the Budapest Treaty at the Deutsche Sammlung von Mikroorganismen (DSM) in Braunschweig, BRD, on May 18, 1993, under the accession number DSM 8310. 
     EXAMPLE 2 
     Expression Plasmid Used For the Preparation of the Fusion Protein 6xHis-NANP-Met-huAmy 
     The expression plasmid pB/E1-6xHis-NANP-Met-huAmy (see FIGS. 4 and 5) was used for the preparation of the fusion protein 6xHis-NANP-Met-huAmy. E. coli M15 cells transformed with plasmids pREP4 and pB/E1-6xHis-NANP-Met-huAmy were deposited in accordance with the Budapest Treaty at the Deutsche Sammlung von Mikroorganismen (DSM) in Braunschweig, BRD, on May 18, 1993, under the accession number DSM 8311. 
     EXAMPLE 3 
     Expression Plasmids Used for the Preparation of the Fusion Proteins 6xHis-NANP-Met-huAmy M35L!, 6xHis-NANP-Met-huAmy M35Q!. 6xHis-NANP-Met-huAmy M35S!, And 6xHis-NANP-Met-huAmy  M35E! 
     The expression plasmids pB/E1-6xHis-NANP-Met-huAmy M35L!, pB/E1-16xHis-NANP-Met-huAmy M35-Q!, pB/E1-6xHis-NANP-Met-huAmy M35S! and PB/E1-6xHis-NANP-Met-huAmy M35E!, which differ from plasmid pB/E1-6xHis-NANP-Met-huAmy only in the nucleotides encoding amino acid 35 of the bA4 amyloid peptide (see FIG. 5), were used for the preparation of the fusion proteins 6xHis-NANP-Met-huAmy M35L!, 6xHis-NANP-Met-huAmy M35Q!, 6xHis-NANP-Met-huAmy M35S! and 6xHis-NANP-Met-huAmy M35E!, respectively. E. coli M15 cells transformed with plasmids pREP4 and pB/E1-6xHis-NANP-Met-huAmy M35L!, pREP4 and pB/E1-6xHis-NANP-Met-huAmy M35Q!, pREP4 and pB/E1-6xHis-NANP-Met-huAmy M35S! and pREP4 and pB/E1-6xHis-NANP-Met-huAmy M35E!!, respectively, were deposited in accordance with the Budapest Treaty at the Deutsche Sammlung von Mikroorganismen (DSM) in Braunschweig, BRD, on May 18, 1993, under the accession numbers DSM 8313, DSM 8314, DSM 8315 and DSM 8312, respectively. 
     EXAMPLE 4 
     Fermentation and Purification of Fusion Proteins 
     Fermentation 
     Plasmids p6xHis-NANP-Met-Amy, pB/E1-6xHis-NANP-Met-huAmy, pB/El 6xHis-NANP-Met-huAmy  M35L!, pB/E1-6xHis-NANP-Met-huAmy M35Q! pB/E1-6xHis-NANP-Met-huAmy  M35S! and pB/E1-6xHis-NANP-Met-huAmy M35E!, respectively were transformed into E. coli M15 cells already containing plasmid pREP4 by standard methods (Sambrook et al., supra). Transformed cells were grown at 37° C. in a 100 l fermenter in Super medium  Stuber et al., Immunological Methods, eds. Lefkovits and Pernis, Academic Press, Inc., Vol. IV, 121-152  1990!! containing 100 mg/l ampicillin and 25 mg/l kanamycin. At an optical density at 600 nm of about 1.0 IPTG was added to a final concentration of 2 mM. After an additional 3 hrs at 37° C. the cells were harvested by centrifugation. In a typical fermentation run a biomass of approximately 500 g containing at least 3 g of the recombinant fusion protein was obtained. 
     Purification 
     2.5 l of 6M guanidine.HCl containing 0.1M di-sodium hydrogen phosphate, pH 8 were added to the cells and stirred for 24 hours. Crude cell debris were removed by centrifugation and the supernatant was then further clarified by cross-flow filtration using a 0.3 mm membrane. The protein contained in the filtrate was then adsorbed to a Ni-NTA column (5 cm×24 cm, flow 20 ml/min). Contaminating E.coli proteins were removed by washing first with 8M urea, pH 7.5. Elution was performed with 8M urea, pH 4. The chromatogram was monitored by SDS-PAGE and fractions containing fusion protein were pooled. A small aliquot of that pool was mixed with EDTA and desalted by dialyzing against water, lyophilized and then analyzed by electron spray mass-spectrometry (Table 1). 
     
                       TABLE 1______________________________________Characterization of the fusion proteins      Purification yield     Average mass      per 100 l fermenter                   Theoretical                             by electronFusion Protein       gram!       mass      spray MS______________________________________Human WT   3.0          13817     13820Human Mut. M35S      5.5          13773     13776Human Mut. M35L      5.7          13799     13802Human Mut. M35Q      4.5          13814     13817Human Mut. M35E      6.0          13813     not testedRat WT     6.0          13724     13728______________________________________ WT = wildtype, Mut = mutant, e.g. M35S (Met at position 35 is mutated to Ser) 
    
     EXAMPLE 5 
     Cleavage of the Fusion Proteins to Yield 1-42 β-amyloid Peptides 
     A semipreparative RP-18 HPLC (Vidac, specification 218TP 152010, 250 mm ×10 mm) column was first equilibrated with 8M urea, pH 4, at a flow rate of 2 ml/min. Then an aliquot of the NTA-eluate containing 400 mg fusion protein in 8M urea, pH 4, was pumped onto the column at a flow rate of 1 ml/min. Then the column was washed with 8M urea, pH 4, at a flow rate of 2 ml/min. The urea was washed out by water at a flow rate of 2 ml/min until baseline adsorbance at the column outlet was reached. Cleavage was performed by flushing the column with 45 mg/ml CNBr in a solution composed of 20% ethanol, 40% formic acid and 40% water for 24 hrs at 22° C. at a flow rate of 0.5 ml/min. The column was then flushed with 0.1M EDTA at a flow rate of 2 ml/min and CNBr together with liberated MRGSHHHHHHGS-(NANP) 19  -RSM was washed out with 0.05% trifluoro acetic acid at a flow rate of 2.0 ml/min. 1-42 residue β-amyloid peptide was eluted at a flow rate of 2 ml/min using the following ethanol gradient given by the time points: (min/% ethanol) 0/0, 40/40, 45/50, 50/65, 55/ 100, 60/100, 65/0 
     A broad peak containing the β-amyloid peptide emerges between 45 and 60 min. Critical for the peptide to be monomeric was the immediate dilution with distilled water (e.g. by dropping the eluate into a stirred beaker containing 200 ml H 2  O), and immediate lyophilization. The resulting powder was named W1. Since a considerable amount of β-amyloid peptide remained on the column, the elution was repeated three times using the above mentioned protocol, giving rise to samples W2, W3 and W4. These samples were tested for purity (Table 2) and the amount of monomeric bA4 (FIG. 6). The correct chemical structure of the peptides was verified by electron spray mass-spectrometry (Table 3), by amino acid analysis and by amino terminal sequencing (Table 3). 
     
                       TABLE 2______________________________________Production of 1-42 β-amyloid peptides     Number of              Wash     Mass produced                                PurityPeptide   tests    Number   (mg)     (%)______________________________________rat WT    4        1        100 ± 14                                90 ± 2(Seq ID No:2)      2        28 ± 8                                89 ± 2              3/4       9 ± 3                                90 ± 1human WT  3        1         96 ± 23                                79 ± 9(Seq ID No:1)      2         52 ± 10                                73 ± 5              3        32 ± 9                                78 ± 4              4        15 ± 8                                86 ± 5human M35S     3        1         71 ± 13                                80 ± 8(Seq ID No:4)      2        31 ± 5                                74 ± 2              3        18 ± 7                                83 ± 2              4         2 ± 7                                88 ± 2human M35L     3        1         59 ± 15                                72 ± 8(Seq ID No:3)      2        23 ± 9                                71 ± 4              3         8 ± 3                                78 ± 3human M35Q     4        1        37 ± 4                                70 ± 2(Seq ID No:5)      2        10 ± 5                                82 ± 3human M35E     1        1        95       not tested(Seq ID No:6)      2        68       not tested              3        46       not tested              4        31       not tested______________________________________ 
    
     Purity is based on amino acid analysis, the content of fusion protein is detected by the quotient of Asp to Glu. Pure 1-42 β-amyloid peptide has 4 GLu and 4 Asp residues, pure fusion protein has a ratio of 42 Asp to 4 Glu. 
     
                       TABLE 3______________________________________Identification of 1-42 β-amyloid peptides   Mass- Spectrometry                Edman degradationSample    Theory  Found      10-15 cycles______________________________________human WT  4515.1   4531**    DAEFRHDSGYEVHHQhuman M35S     4471.0  4472       DAERHDSGYhuman M35L     4497.1  4498       DAEFHDSGYhuman M35Q     4512.0  4512       not testedhuman M35E     4513.0  4512       not testedrat WT    4417.0   4435**    DAEFGHDSGF______________________________________ **The methionines of human WT and rat WT were transformed during the cleavage procedure to methionine sulfoxide. 
    
     EXAMPLE 6 
     Purification of Monomeric 1-42 bA4 
     Small scale method 
     Samples containing 1 mg of bA4 were applied to a LKB UltroPac HPLC column (diameter: 7.5 mm, length :600 mm, flow 0.5 ml/min, buffer: 12 mM Tris(hydroxymethyl)aminomethan containing 200 mM glycine, pH 7.8). bA4 emerged in a sharp peak, and the peak fractions contained the Coomassie blue band on the agarose electrophoresis gel shown in FIG. 7. Light-scattering experiments gave no evidence of high molecular weight forms (aggregates or fibres) and calibration standards which were chromatographed under identical conditions pointed to a molecular weight of about 4500, indicating that bA4 was present as a monomer. 
     Preparative Scale Method 
     The &#34;Continuous Elution Electrophoresis system Model 491 Prep Cell&#34; from BioRad was used. The non-denaturating discontinuous acrylamide gel was composed of a 4% acrylamide/2.7% N,N&#39;-methylene-bis-acrylamide separating gel in 0.375M Tris(hydroxymethyl) amino-methan (pH 8.8) with a length of 3 cm and a diameter of 37 mm, and equipped with a cooling tube of 20 mm diameter. 
     The stacking gel was composed of 4% acrylamide/2.7% N,N&#39;-methylenebis-acrylamide in 0.125M Tris(hydroxymethyl)amino-methane (pH 6.8) and had a length of 2 cm. The running buffer was 25 mM Tris(hydroxymethyl)aminomethan/0.2M glycine, pH 8.3. For elution the same buffer was used with a flow rate of 0.75 ml/minutes. 45 mg of bA4 peptide, generally from wash 2, 3 or 4, were dissolved in 7 ml H 2  O and 1 ml glycerol. Electrophoresis was performed at 12 watts (constant, limits at 500 V and 40 mA), a typical run requiring 4 hours. The results of a typical run are shown in FIG. 7. 
     EXAMPLE 7 
     Purification of 1-35 HIV-1 Peptide 
     400 mg fusion protein MRGS (H) 6  GS (NANP) 19  RSM RILA VERYLKDQQLLGIWGCSGKLICTTAVPWNAS (Seq ID No: 12) prepared and purified by the same methods as those described for the preparation and purification of the fusion proteins containing monomeric 1-42 bA4 (Examples 1-4) were loaded onto a VYDAC RP 18 column (specification 218 TP 152010, 250 mm×10 mm) and cleaved using the same conditions as those described for the cleavage of the 1-42 bA4 fusion proteins (Example 5). Approximately 20-30 mg of lyophilized powder were obtained. This powder was analyzed by electron spray analysis. A peak of 3902±2 Da corresponding to the 1-35 HIV-1 peptide (Seq ID No: 11) was detected. 
     The present invention has been described in terms of its preferred embodiments. However, after reading the present specification various alternative embodiments will become apparent to those skilled in the art. 
     These variations are to be considered within the scope and spirit of the subject invention, which is only to be limited by the claims which follow and their equivalents. 
     
         __________________________________________________________________________SEQUENCE LISTING(1) GENERAL INFORMATION:(iii) NUMBER OF SEQUENCES: 12(2) INFORMATION FOR SEQ ID NO: 1:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 42 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(v) FRAGMENT TYPE: N-terminal(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1:AspAlaGluPheArgHisAspSerGlyTyrGluValHisHisGlnLys151015LeuValPhePheAlaGluAspValGlySerAsnLysGlyAlaIleIle202530GlyLeuMetValGlyGlyValValIleAla3540(2) INFORMATION FOR SEQ ID NO: 2:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 42 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(v) FRAGMENT TYPE: N-terminal(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 2:AspAlaGluPheGlyHisAspSerGlyPheGluValArgHisGlnLys151015LeuValPhePheAlaGluAspValGlySerAsnLysGlyAlaIleIle202530GlyLeuMetValGlyGlyValValIleAla3540(2) INFORMATION FOR SEQ ID NO: 3:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 42 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(v) FRAGMENT TYPE: N-terminal(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 3:AspAlaGluPheArgHisAspSerGlyTyrGluValHisHisGlnLys151015LeuValPhePheAlaGluAspValGlySerAsnLysGlyAlaIleIle202530GlyLeuLeuValGlyGlyValValIleAla3540(2) INFORMATION FOR SEQ ID NO: 4:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 42 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(v) FRAGMENT TYPE: N-terminal(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 4:AspAlaGluPheArgHisAspSerGlyTyrGluValHisHisGlnLys151015LeuValPhePheAlaGluAspValGlySerAsnLysGlyAlaIleIle202530GlyLeuSerValGlyGlyValValIleAla3540(2) INFORMATION FOR SEQ ID NO: 5:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 42 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(v) FRAGMENT TYPE: N-terminal(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 5:AspAlaGluPheArgHisAspSerGlyTyrGluValHisHisGlnLys151015LeuValPhePheAlaGluAspValGlySerAsnLysGlyAlaIleIle202530GlyLeuGlnValGlyGlyValValIleAla3540(2) INFORMATION FOR SEQ ID NO: 6:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 42 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(v) FRAGMENT TYPE: N-terminal(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 6:AspAlaGluPheArgHisAspSerGlyTyrGluValHisHisGlnLys151015LeuValPhePheAlaGluAspValGlySerAsnLysGlyAlaIleIle202530GlyLeuGluValGlyGlyValValIleAla3540(2) INFORMATION FOR SEQ ID NO: 7:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 520 base pairs(B) TYPE: nucleic acid(C) STRANDEDNESS: single(D) TOPOLOGY: linear(ii) MOLECULE TYPE: DNA (genomic)(ix) FEATURE:(A) NAME/KEY: CDS(B) LOCATION: 115..516(D) OTHER INFORMATION: /product=&#34;Amyloid Protein AA&#34;(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 7:CTCGAGAAATCATAAAAAATTTATTTGCTTTGTGAGCGGATAACAATTATAATAGATTCA60ATTGTGAGCGGATAACAATTTCACACAGAATTCATTAAAGAGGAGAAATTAACTATG117MetAGAGGATCGCATCACCATCACCATCACGGATCTAACGCGAACCCGAAC165ArgGlySerHisHisHisHisHisHisGlySerAsnAlaAsnProAsn51015GCGAACCCGAACGCGAACCCGAACGCGAACCCGAACGCGAACCCGAAC213AlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsn202530GCGAACCCGAACGCGAACCCGAACGCGAACCCGAACGCGAACCCGAAC261AlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsn354045GCGAACCCGAACGCGAACCCGAACGCGAACCCGAACGCGAACCCGAAC309AlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsn50556065GCGAACCCGAACGCGAACCCGAACGCGAACCCGAACGCGAACCCGAAC357AlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsn707580GCGAACCCGAACGCGAACCCGAGATCTATGGATGCGGAGTTCGGACAT405AlaAsnProAsnAlaAsnProArgSerMetAspAlaGluPheGlyHis859095GATTCAGGCTTCGAAGTCCGCCATCAAAAACTGGTGTTCTTTGCAGAA453AspSerGlyPheGluValArgHisGlnLysLeuValPhePheAlaGlu100105110GATGTGGGTTCAAACAAAGGTGCCATCATTGGACTCATGGTGGGTGGC501AspValGlySerAsnLysGlyAlaIleIleGlyLeuMetValGlyGly115120125GTTGTCATAGCATAAGCTT520ValValIleAla130(2) INFORMATION FOR SEQ ID NO: 8:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 133 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: protein(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 8:MetArgGlySerHisHisHisHisHisHisGlySerAsnAlaAsnPro151015AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro202530AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro354045AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro505560AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro65707580AsnAlaAsnProAsnAlaAsnProArgSerMetAspAlaGluPheGly859095HisAspSerGlyPheGluValArgHisGlnLysLeuValPhePheAla100105110GluAspValGlySerAsnLysGlyAlaIleIleGlyLeuMetValGly115120125GlyValValIleAla130(2) INFORMATION FOR SEQ ID NO: 9:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 520 base pairs(B) TYPE: nucleic acid(C) STRANDEDNESS: single(D) TOPOLOGY: linear(ii) MOLECULE TYPE: DNA (genomic)(ix) FEATURE:(A) NAME/KEY: CDS(B) LOCATION: 115..516(D) OTHER INFORMATION: /product=&#34;Amyloid Protein AA&#34;(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 9:CTCGAGAAATCATAAAAAATTTATTTGCTTTGTGAGCGGATAACAATTATAATAGATTCA60ATTGTGAGCGGATAACAATTTCACACAGAATTCATTAAAGAGGAGAAATTAACTATG117Met1AGAGGATCGCATCACCATCACCATCACGGATCTAACGCGAACCCGAAC165ArgGlySerHisHisHisHisHisHisGlySerAsnAlaAsnProAsn51015GCGAACCCGAACGCGAACCCGAACGCGAACCCGAACGCGAACCCGAAC213AlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsn202530GCGAACCCGAACGCGAACCCGAACGCGAACCCGAACGCGAACCCGAAC261AlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsn354045GCGAACCCGAACGCGAACCCGAACGCGAACCCGAACGCGAACCCGAAC309AlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsn50556065GCGAACCCGAACGCGAACCCGAACGCGAACCCGAACGCGAACCCGAAC357AlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsn707580GCGAACCCGAACGCGAACCCGAGATCTATGGATGCGGAGTTCCGTCAT405AlaAsnProAsnAlaAsnProArgSerMetAspAlaGluPheArgHis859095GATTCAGGCTATGAAGTCCACCATCAAAAACTGGTGTTCTTTGCAGAA453AspSerGlyTyrGluValHisHisGlnLysLeuValPhePheAlaGlu100105110GATGTGGGTTCAAACAAAGGTGCCATCATTGGACTCATGGTGGGTGGC501AspValGlySerAsnLysGlyAlaIleIleGlyLeuMetValGlyGly115120125GTTGTCATAGCATAAGCTT520ValValIleAla130(2) INFORMATION FOR SEQ ID NO: 10:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 133 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: protein(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 10:MetArgGlySerHisHisHisHisHisHisGlySerAsnAlaAsnPro151015AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro202530AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro354045AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro505560AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro65707580AsnAlaAsnProAsnAlaAsnProArgSerMetAspAlaGluPheArg859095HisAspSerGlyTyrGluValHisHisGlnLysLeuValPhePheAla100105110GluAspValGlySerAsnLysGlyAlaIleIleGlyLeuMetValGly115120125GlyValValIleAla130(2) INFORMATION FOR SEQ ID NO: 11:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 35 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 11:ArgIleLeuAlaValGluArgTyrLeuLysAspGlnGlnLeuLeuGly151015IleTrpGlyCysSerGlyLysLeuIleCysThrThrAlaValProTrp202530AsnAlaSer35(2) INFORMATION FOR SEQ ID NO: 12:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 126 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: protein(xi) SEQUENCE DESCRIPTION: SEQ ID NO: 12:MetArgGlySerHisHisHisHisHisHisGlySerAsnAlaAsnPro151015AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro202530AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro354045AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro505560AsnAlaAsnProAsnAlaAsnProAsnAlaAsnProAsnAlaAsnPro65707580AsnAlaAsnProAsnAlaAsnProArgSerMetArgIleLeuAlaVal859095GluArgTyrLeuLysAspGlnGlnLeuLeuGlyIleTrpGlyCysSer100105110GlyLysLeuIleCysThrThrAlaValProTrpAsnAlaSer115120125__________________________________________________________________________