Abstract:
A method of assembling a protein nanostructure on a surface including selectively patterning a surface with a fixation site, bringing a protein node into contact with the surface, and allowing the protein node to bond with the fixation site, so that the position and/or orientation of the protein node is constrained, and compositions.

Description:
This application is a National Stage of International Application No. PCT/US2010/34248, filed May 10, 2010, which claims the benefit of U.S. Provisional Application No. 61/177,256, filed May 11, 2009. 
     This application hereby incorporates the specifications of U.S. Provisional Application No. 60/996,089, filed Oct. 26, 2007, International Application No. PCT/US2008/012174, filed Oct. 27, 2008 (published as international publication WO2009/055068 on Apr. 30, 2009), U.S. Provisional Application No. 61/173,114, filed Apr. 27, 2009, U.S. Nonprovisional application Ser. No. 12/766,658, filed Apr. 23, 2010, U.S. Provisional Application No. 61/136,097, filed Aug. 12, 2008, U.S. Provisional Application No. 61/173,198, filed Apr. 27, 2009, U.S. Nonprovisional application Ser. No. 12/589,529, filed Apr. 27, 2009, International Application No. PCT/US2009/053628, filed Aug. 13, 2009 (published as international publication WO2010/019725 on Feb. 18, 2010), U.S. Provisional Application No. 61/246,699, filed Sep. 29, 2009, and U.S. Provisional Application No. 61/177,256, filed May 11, 2009 in their entirety by reference. All documents cited herein or cited in any one of the specifications incorporated by reference are hereby incorporated by reference. 
    
    
     This invention was made with government support under grant numbers 1 R43 GM080805-01A1 and 1 R43 GM077743-01A1 awarded by the National Institutes of Health. The government has certain rights in the invention. 
    
    
     SUMMARY OF THE INVENTION 
     A method according to the invention of assembling a protein nanostructure on a surface can include selectively patterning a surface with at least one fixation site, bringing at least one protein node into contact with the surface, and allowing the at least one protein node to bond with the fixation site, so that the position and/or orientation of the at least one protein node is constrained. The protein node can include an interaction domain. The interaction domain of a first protein node can interact with the interaction domain of a second protein node, so that the position and/or orientation of the first protein node with respect to the position and/or orientation of the second protein node is constrained. The protein node can rotate about an axis normal to the surface. The protein node can be a substantially C3-symmetric, substantially C4-symmetric, or substantially C6-symmetric protein node. The protein node can include a plurality of subunits. The plurality of protein nodes can be bonded to fixation sites to form an extended structure on the surface. The plurality of protein nodes can be bonded to fixation sites to form a repeating structure or tessellation on the surface. The interaction domains of two or more protein nodes can interact to lock the protein nodes into a final desired orientation on the surface. The at least one protein node can be linked to a streptavidin protein. Two protein nodes can be linked to each other through a streptavidin protein. The surface can include a solid surface. The surface can include silicon, silicon oxide, carbon, graphene, and/or a semiconductor. The fixation site can include an atom or a cluster of atoms. The atom or cluster of atoms can be selected from the group consisting of metal, a noble metal, and gold, which can be deposited onto the surface. A terminal cysteine group on the at least one protein node can bond with the fixation site. The surface can be selectively patterned with the fixation site by depositing a metal, noble metal, or gold atom or cluster of atoms onto the surface with an atomic force microscope tip. The interaction domain of the first protein node and the interaction domain of the second protein node can interact through an electrostatic, a hydrogen bonding, a hydrophobic, and/or a van der Waals interaction. The strength of the interaction between the interaction domain of the first protein node and the interaction domain of the second protein node can dependent on an external condition. The external condition can include pH, temperature, chemical species concentration, light and/or other radiation exposure, electric field, magnetic field, and/or another external condition. 
     In an embodiment according to the invention, a protein nanostructure can include a protein node and a selectively patterned surface having at least one fixation site, the protein node bonded with the at least one fixation site, or a binding domain comprising a sequence of amino acid residues, the protein node comprising a plurality of subunits, the subunits covalently linked through a sequence of amino acid residues, and the binding domain covalently linked to a subunit. The protein nanostructure can include a selectively patterned surface having at least one fixation site and a protein node bonded with the at least one fixation site. The protein node can be bonded with the at least one fixation site through a covalent, van der Waals, and/or thiol-gold bond. The protein nanostructure can include a first antibody protein. The protein node can include a first protein binding domain and the first antibody protein can be bound to the first protein binding domain. The protein nanostructure can include a streptavidin bound to an adaptor protein having a second protein binding domain and a second antibody protein different from the first antibody protein. The second antibody protein can be bound to the second protein binding domain. The streptavidin can be bound to the protein node. A biosensor can include the protein nanostructure. 
     A kit according to the invention can includea selectively patterned solid surface having at least one fixation site and a protein node. The protein node can bond with the at least one fixation site. 
     In an embodiment according to the present invention, a first binding domain can be covalently linked to the subunit of the protein node to form a binding domain node, and the first binding domain can bind an Ig (immunoglobulin) or antibody. For example, the first binding domain can be a Protein G domain and/or bind an IgG (immunoglobulin G). A streptavidin can be bound to an adaptor protein having a second binding domain that can bind a second immunoglobulin. The streptavidin can be bound to the binding domain node. The second binding domain can bind a second immunoglobulin that is different from the first immunoglobulin that the first binding domain binds. 
     In a method according to the present invention, a streptavidin or streptavidin derivative can be reacted with a thiol-reactive azido-ATP reagent to form an azido-ATP modified streptavidin. An Ig (immunoglobulin) and a dimeric ATP-binding protein incorporating fused binding domains can be allowed to interact to form a first complex. The first complex can be photocrosslinked with the azido-ATP modified streptavidin to form a second complex. The second complex can be allowed to bind with a single chain protein node having a fused binding domain and a bound Ig. 
     In this text, including the claims, a reference to one item is to be understood as encompassing a reference to two or more items. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a scheme for a scalable architecture for nanotechnology. 
         FIG. 2  illustrates an engineered streptavidin adaptor. 
         FIG. 3  illustrates C3 and C4-symmetric nodes and streptavidin complexes. 
         FIG. 4  illustrates single chain C3 and C4-symmetric nodes with reduced ligation. 
         FIG. 5  illustrates a hierarchy of protein-based nanostructure architecture. 
         FIG. 6  illustrates an example of the assembly of nanostructures using a combination of top-down and bottom-up approaches. 
         FIG. 7  illustrates functional nanostructure components for sensor and biomedical applications. 
         FIG. 8  illustrates examples of biosensor architecture. 
         FIG. 9  illustrates protein nodes. 
         FIG. 10  illustrates reagents and protein components for nanoassembly fabrication. 
         FIG. 11  illustrates a convergent method for assembling functionalized nanostructures. 
         FIG. 12  illustrates nanostructures functionalized with bound antibodies. 
     
    
    
     DETAILED DESCRIPTION 
     The ability to control the structural and functional properties of materials at the nanoscale can enable technologies in areas such as energy, water purification, semiconductor device fabrication, and medical devices. A common underlying approach, embodied in a scalable architectural platform, can allow the fabrication of materials and devices with features at the nanoscale using a uniform assembly strategy and enable the broad applicability of nanotechnology. 
     A flexible and scalable technology platform for nanotechnology can use a combination of top-down and bottom-up self-assembly methods. Engineered proteins, polymers that are able to spontaneously self-assemble to organize thousands of atoms with atomic precision, can play a role in the platform. A flexible set of architectural components can be assembled into an essentially infinite set of engineered nanostructures with one, two, and three-dimensional organization. 
     In an embodiment, nanostructures can be assembled with proteins. The protein nanostructures can themselves be the basis for functional biomaterials. In another embodiment, the organized structures formed of the protein materials can essentially serve as a resist or template, enabling the patterning of other materials. Hybrid structures can incorporate nanostructures using a combination of these methods, for example, (1) using the protein nanostructures themselves as the basis for functional biomaterials, and (2) using organized structures formed of protein materials as a resist or template for the patterning of other materials (see,  FIG. 1 ). 
       FIG. 1  illustrates that known and to be determined 3-dimensional (3D) structures of thermostable proteins (A) and methods of protein engineering (computer modeling, site specific modification, recombinant DNA technology, protein expression, etc.) can be used as a basis for creating a flexible set of nanoscale components (B) that can be assembled into 1, 2, and 3-dimensional structures (e.g., see,  FIG. 5 ). The assembled nanostructures can have, for example, two different types of applications. For example, a first set of assembly applications (C) can be functional assemblies, where the underlying protein architecture has been modified, e.g., through the attachment of immunoglobulins, binding molecules, growth factors, reporter enzymes, adhesion molecules, etc., so that the protein architecture forms a functional biological interface. Applications include, e.g., biosensors for pathogen and/or disease marker diagnosis, active membranes for water purification and filtration, and substrate materials for biomaterials such as artificial skin, cartilage, and bone. A second set of assembly applications (D) involves using the protein-based nanoarchitecture as a resist or patterning agent that can be used to pattern semiconductor materials or be coated with metal. The protein nanoarchitecture can be used for initial patterning, but can be subsequently physically removed from the assembly by etching or heating. The patterns developed from using the protein nanoarchitecture as a resist or pattern can be used as a step in a semiconductor fabrication process or to generate stamps using soft lithography processes. Fabrication methods may used together to produce hybrid structures (E), where, e.g., substrate nanostructures are produced using soft lithography and coated with functional protein nano-architectures. 
     A nanometer is 1×10 −9  meters, roughly equivalent to the length of a carbon atom chain nine atoms long, and substantially less that the wavelength of visible light (˜400 nM). There are a number of advantages to being able to control assembly architecture at the nanoscale. Examples of such advantages can include the following: 
     Miniaturization: The efficiency of electronic or memory devices ultimately devolves on maximizing the density with which discrete components can be manufactured on an appropriate substrate. Silicon-based semiconductor fabrication technology has continuously progressed over the last 40 years according to Moore&#39;s Law, with an approximate doubling in device density every two years. As a result, processes are now in place or under development that will produce integrated circuits with 45 nm features. Although there have been many (incorrect) predictions made in recent years that practical limits to device miniaturization had been reached, pushing device densities beyond the latest generation may be subject to fundamental physical limitations (International Technology Roadmap for Semiconductors (http://www.itrs.net/reports.html)). 
     Emergence of New Properties: The emergence of new properties in very small systems can be exploited for development of new kinds of functional devices. Examples of such new properties include, for example, effects that stem from statistical or quantum characteristics that emerge in very small systems and novel physical characteristics that emerge through the interaction of light with structures having sub-optical wavelength dimensions. 
     Biological System Interfaces: Materials and/or devices can directly interact with biological systems and/or directly incorporate biological macromolecules as intrinsic structural or functional components. Functionality and interaction specificity of biological systems is manifest in the structure of macromolecules structurally organized at the nanoscale, principally proteins and nucleic acids, which in a sense are respectively specialized for structure-function and information storage and processing roles. Most proteins organized as folded polymers of amino acids have subunit structures that self-organize thousands of atoms with atomic precision over ranges of 1 to 100 nm, and manifest a wide range of structural, catalytic, binding, and signal transducing properties. Many proteins can intrinsically, or be engineered to bind to surfaces with a defined orientation, a characteristic that can be important in processes such as active filtration, directional transport of chemical substances, or charge storage on surfaces. Rich functionally of proteins can physically arise from near equivalence of several different types of interaction forces (e.g., electrostatic, van der Waals interaction, and solvation effects) and the corresponding effects of statistical energy fluctuations on the order of a few kT that dominate the behavior of biological systems on the molecular scale (Phillips &amp; Quake, 2006). 
     Scalability: Scalability can enable the broad application of a manufacturing technology. In the context of engineered nanostructures, scalability can have, for example, two different aspects. A first aspect involves the ability to manufacture structures using a parallel manufacturing process. For example, early conceptions of nanostructure fabrication—motivated by studies demonstrating the ability to manipulate single atoms using atomic force microscopy—envisioned that devices could be assembled essentially atom by atom using molecular scale atomic manipulators (Drexler, 1992). However, this may be an impractical process for assembling many devices owing to the time required to perform what is intrinsically a serial process that would have to repeated many thousands (if not millions) of times per individual nanostructure. As outlined below, the combination of a top-down approach, able to specify the position of a few nucleation sites, coupled with a self-assembly process around each of the nuclei, can produce highly engineered nanostructures in a parallel production mode. 
     A second aspect of scalability applies to the use of nanostructures for intrinsically large-scale applications like water purification which may require active membrane structures that are, on the one hand, organized on the nanostructural level, but on the other, manufactured as membrane assemblies on very large scale to have useful capacity. Additional applications that can lead to very large-scale assemblies include energy storage devices or photovoltaic cells. Engineered proteins can ultimately be produced in plants for a few dollars a pound. (http://www.sciencedaily.com/releases/1999/07/990715134504.htm). 
     An engineered streptavidin adaptor based on a protein, can, for example, act as a controllable component adaptor for linking streptavidin strut structures. For example, an engineered streptavidin adaptor can act as a reversible protecting group for pairs of streptavidin binding sites, and provide precise control over nanostructure assembly. Nanostructures can incorporate components such as engineered streptavidin adaptors (also termed streptavidin macromolecular adaptors (SAMAs)) and protein nodes. SAMAs, structures constructed from SAMAs and/or streptavidin tetramers, ways of making SAMAs and structures incorporating SAMAs, and ways of using SAMAs and structures incorporating SAMAs are described in the international publication number WO2009/055068 (published Apr. 30, 2009, publication of international application number PCT/US2008/012174, filed Oct. 27, 2008), which is hereby incorporated by reference in its entirety. 
     A protein node can be a protein that serves as a connector. A protein node can have one or more attachment points with defined, for example, nonlinear, geometry. Nodes can be linked together, for example, with streptavidin struts, to establish the topology of a structure. For example, a protein node can be based on a protein that has multiple subunits arranged symmetrically. Protein nodes, structures constructed using nodes, ways of making nodes and structures incorporating nodes, and ways of using nodes and structures incorporating nodes are described in the international publication number WO2010/019725 (published Feb. 18, 2010, publication of international application number PCT/US2009/053628, filed Aug. 13, 2009), which is hereby incorporated by reference in its entirety. 
     A fixation site can, for example, be a location on a surface that constrains the position and/or orientation of a protein node that is linked or bonded to the fixation site. That is, a fixation site can be a point of immobilization for a protein node. For example, a protein node bonded to a fixation site may be able to rotate, but not to translate relative to the surface. Alternatively, a protein node may be bonded to a fixation site, so that it can neither rotate nor translate relative to the surface. Two (or more) protein nodes that are bonded to fixation sites that are able to rotate, but not translate, with respect to the surface may also have interaction domains. The interaction domains of the two (or more) protein nodes may interact to further constrain the motion of the protein nodes, for example, to constrain the rotation as well as the translation of the protein nodes relative each other and/or to the surface. For example, the interaction domain of a first protein node and the interaction domain of a second protein node can interact through electrostatic, hydrogen bonding, hydrophobic, and/or van der Waals interactions. 
     For example,  FIG. 2  illustrates an engineered streptavidin adaptor. Part a. schematically shows a streptavidin tetramer that has two biotin binding sites free and two sites occupied by biotin groups attached to biotin-azido-ATP (adenosine triphosphate) cross-link molecules that link streptavidin to a dimeric ATP binding protein (e.g., a SAMA). The pair of dots at the extreme left of the structure shown in part a. indicate cysteine sites that can be biotinylated. Part b. shows a schematic of the biotinylated complex, which “regenerates” streptavidin binding activity and gives the effect of a “reversible” protecting group for two of the four biotin binding sites on streptavidin. Incorporation of these adaptors into strut assemblies, for example, streptavidin strut assemblies, allows the controlled assembly of streptavidin linked nanostructures. Part c. shows streptavidin docked with the thermostable, dimeric ATP binding protein MJ0577 (pdb code: 1MJH) that can be used as a reversible protecting group (e.g., a SAMA) for streptavidin for nanostructure assembly applications. Adaptor proteins (e.g., SAMAs) can also be engineered to incorporate functional domains like immunoglobulin binding domains useful in biosensors (see,  FIG. 7 ). 
       FIG. 3  illustrates C3 and C4-symmetric nodes and streptavidin complexes. The top row of images (parts a., b., and c.) shows C3-symmetric node:streptavidin complexes in space filling molecular representation (a.), polypeptide backbone ribbon representation (b.), and schematic representation (c.). The carbonic anhydrase from the thermophilic microorganism  Methanosarcina thermophila  (pdb code 1thj) can be used as a template for the C3 node. The bottom row of images (parts d., e., and f.) shows corresponding C4-symmetric node:streptavidin complexes. The C4 template node protein shown is the IPP isomerase from the thermophilic microorganism  Thermus thermophilus  (pdb code 1vcg). 1stp is the Protein Data Bank (pdb) code for streptavidin. Nodes can also be, for example, C6-symmetric protein nodes. For example, two or more protein nodes can be linked to each other through a streptavidin protein. 
       FIG. 4  illustrates single chain C3 and C4-symmetric nodes with reduced ligation. Protein engineering and recombinant DNA methods can be used to connect subunits of symmetric node structures into a single polypeptide chain. This allows a reduction in the number of biotinylation sites in a structure, resulting in an expanded set of node structures with defined geometry and ligation number for attached streptavidin struts. The top row of  FIG. 4  shows C3 symmetric single-chain structures, including a 120 degree divalent node connector and a monovalent cap. The bottom row shows various possibilities for C4 single-chain ligation number and geometry. These constructs can be, for example, based on the template proteins shown in  FIG. 3 . 
       FIG. 5  illustrates a hierarchy of protein-based nanostructure architecture. Nature affords a large number of thermostable multimeric proteins potentially useful for 1D, 2D, and 3-dimensional nanostructure assemblies. These include both infinite (lattice) and finite structures. Some of these structures are shown in  FIG. 5 . 
       FIG. 6  illustrates an example of the assembly of nanostructures using a combination of top-down and bottom-up approaches. Part a. shows a C4-symmetric node with polypeptide termini enabling it to chemically bind to a substrate surface; e.g., through reaction of orienting cysteine thiol groups, for example, a terminal cysteine group, on the protein polypeptide chain with gold atoms on a substrate surface. Part b. shows a 1:1 complex of streptavidin with a C4-single-chain capping group. The single-chain capping group subunits can form geometrically defined interactions with subunits of other C4-single-chain capping groups (interactions shown schematically in Part c.). Part d. shows a surface, e.g., a substrate material, that has been selectively or precision patterned with a few fixation sites, for example, chemically reactive sites, such as an atom or one or more small clusters of gold atoms, noble metal atoms, metal atoms, or other atoms positioned using atomic force microscopy, for example, with an atomic force microscope tip, or other methods. For example, the surface can include a solid surface. For example, the surface can include a semiconductor, silicon, silicon oxide, carbon, and/or graphene. Part e. shows these sites as fixation points, or points of immobilization, for example, that constrain the position and/or orientation of biotin-functionalized C4 nodes; e.g., through reaction and/or bonding of the gold atoms with terminal cysteine thiol groups on the protein polypeptide chain. Nodes immobilized at this stage can have substantial flexibility in orientation. For example, an immobilized node can rotate about an axis normal to the surface. Part f. shows the result of addition of a streptavidin:C4 single-chain capping node complex to form a finite patterned structure. Part g. shows the structure “fixed” through interactions (small rectangle boxes) formed between the terminal single chain nodes when they are in proper relative orientation and proximity. According to the final pattern of static interactions that are desired in the structure, the terminal groups (e.g., the single-chain C4 node structures in part b.) can be engineered to incorporate interaction domains, for example, chemically reactive or structurally interacting polypeptide domains (small rectangle boxes in part g.) that will “lock” the components into their final desired orientation. For example, the interaction domain of a first protein node and the interaction domain of a second protein node can interact through electrostatic, hydrogen bonding, hydrophobic, and/or van der Waals interactions. 
     In an embodiment, the strength of an interaction between an interaction domain of a first protein node and an interaction domain of a second protein node can be dependent on an external condition. Examples of such external conditions include pH, temperature, chemical specifies concentration, light or other radiation exposure, an electric field, a magnetic field, and/or another external condition. For example, the strength of an interaction can be characterized by the energy required to achieve separation of the first protein node from the second protein node. 
     An arbitrarily large number of finite and semi-infinite “tessellated” or repeating structures or extended structures can be created using this approach, where the initial immobilization of only a few atoms, or clusters of atoms, can serve to restrict the organizational degrees of freedom the structure can subsequently assume as it is progressively assembled. 
       FIG. 7  illustrates functional nanostructure components for sensor and biomedical applications. Protein-based nanostructures can be functionalized by incorporation or attachment of prosthetic groups, dyes, or other proteins with binding, sensing, or catalytic function. As an example, part a. diagrammatically shows a site-modified form of streptavidin that is modified to allow chemical reaction with a modified adaptor protein (see  FIG. 2 ) incorporating immunoglobulin (IgG) protein binding domains. Part c. shows a single-chain C3 symmetric node where one chain has been modified to covalently incorporate a polypeptide sequence encoding a different IgG binding domain. Parts b. and d. show schematic representations, because such structures can be engineered, so that the IgG binding domains project from the plane of the underlying architecture, to facilitate simultaneous binding of, e.g., two different IgGs to the same antigen. 
       FIG. 8  illustrates examples of biosensor architecture. Parts a. through d. show schematic representations (using the representations of  FIG. 7 ) of various nanoarray assemblies built using components shown in  FIGS. 3 ,  4 , and  7 , and incorporating immobilized antibodies in close proximity. Specifically, the components outlined in  FIG. 7  can be used together with other Cn-symmetry nodes to produce a variety of 2D sensor architectures. These can include small arrays like those shown in parts a. and b., or extended lattices (parts c. and d.). Structures like a., b., and c. potentially allow simultaneous attachment of two different antibodies (for example, different antibodies attached to the streptavidin tetramers than are attached to the C3-symmetric nodes) able to simultaneously bind to two different epitopes on an antigen. Interaction with simultaneous, but different binding sites on an antigen can increase affinity and specificity for antigen binding, for example, by several orders of magnitude. In the unbound state, the surface bound IgG molecules can be relatively flexible, but can become relatively immobilized on antigen binding. Immobilization of the antigen can be detected using a number of different biophysical methods including surface plasmon resonance (SPR, Smith &amp; Corn 2003) or fluorescence resonant energy transfer (FRET, Lackowitz 1999) methods. 
     The components shown in  FIGS. 9 and 10  embody, for example, three types of functions: 1) node components with different strut-binding geometry and ligation number that control nanostructure architectural features, 2) strut components that interconnect the nodes, and 3) reagents and engineered adaptor proteins that facilitate controlled assembly of the nanostructures or the attachment of additional proteins that can confer functionality on the underlying nanostructure architecture. Multiple functions can be combined in a single molecular component, as, for example, in the single-chain C3 nodes incorporating the integrally fused IgG binding domain ( FIG. 9 . center row). For example, the binding domain can be a Protein G domain. Different approaches can be used to control nanostructure assembly. A first approach involves a thiol-reactive iminobiotin reagent. Since iminobiotin binding to streptavidin is pH-dependent (dissociating at mildly acid pH), this reagent can be used in many ways to control what may otherwise be spontaneous and irreversible streptavidin:biotin interactions and may be particularly important to allow “annealing” in extended 2D assemblies. A second approach involves a reversible protecting group for 2 of the binding sites on streptavidin, a “streptavidin macromolecular adapter protein” or “SAMA”. This construct offers a level of controlled nanostructure assembly, as, for example, illustrated in  FIG. 2 , for example, for assembling an extended strut. The SAMA is based on a dimeric protein, having 2 ATP binding sites that are geometrically complementary to 2 biotin binding sites on streptavidin, that has been additionally engineered to incorporate two cysteine residues that can be subsequently biotinylated to regenerate streptavidin binding capability while preserving overall strut geometry. 
       FIG. 10  shows additional reagents and modular components useful in functional nanoassembly fabrication, including a variant dimeric ATP-binding protein ( FIG. 10   h ) (e.g., a SAMA) incorporating fused, IgG-binding protein-G domains. Biotinylated IgG binding domains that can be directly connected to streptavidin via biotinylation linkers ( FIG. 10 ) are available from research biochemical suppliers (www.piercenet.com) as are additional reagents (www.quantabiodesign.com) and antibodies outlined in  FIG. 10 . Reagents and protein components for nanoassembly fabrication shown in  FIG. 10  are as follows. Part a shows a schematic illustration of streptavidin with 4 biotin binding sites. Part b shows an engineered streptavidin (Streptavipol) incorporating 4 surface cysteine sites aligned along a molecular dyad axis, so that they are geometrically complementary with 2 biotin binding sites on streptavidin. Part c shows show a streptavidin macromolecular adaptor (SAMA) based on an engineered form of a dimeric ATP binding protein. Part d shows an SH-reactive biotinylation reagent. Part e shows an SH-reactive azido-ATP linking reagent. Part f shows a biotin-azido-ATP bifunctional crosslinking reagent. Part h shows a dimeric ATP binding protein incorporating a protein-G IgG binding domain. Part g shows biotinylated Protein G. Parts i,j show two different IgG molecules. 
     In an embodiment, immobilized antibody arrays are generated (for example, the immobilized species can be IgGs, Fabs, or single-chain Fvs, depending on the application) with controlled geometry. 
     Improvements in detector affinity and specificity can be associated with organized, high density immobilization of IgGs on sensor array surfaces (e.g., Soukka et al., Anal. Chem., v.73 (2001) pp. 2254-2260). With the constructs and devices presented herein one can control and precisely position the relative orientation of two (or ultimately more) IgG molecules to a substrate surface, e.g., attach to different epitopes of an antigen simultaneously.  FIG. 11  illustrates how some of the components described above can be used in a convergent synthesis to assemble a small component incorporating 2 pairs of different antibodies in close proximity. Part a shows a Streptavipol ( FIG. 10   b ) tetramer reacting with a thiol-reactive azido-ATP reagent to produce an azido-ATP modified Streptavipol tetramer. Parts c and d show the interaction between a given IgG and a dimeric ATP-binding protein incorporating fused Protein-G domains, to form the complex Part e. Two moles of Part e can associate with the Streptavipol and subsequently be photo-crosslinked to form the element of part f. Part f can then bind two C3-single chain nodes with fused IgG binding domains and attached IgG molecules to form the structure in Part h, incorporating two sets of two different antibodies in close proximity to each other. The structures of Streptavipol and a trimeric single-chain fusion (see, e.g.,  FIG. 7 ) can orient the IgGs in a direction normal to the plane of the page in which the schematic is drawn as illustrated in the inset part i. and used in  FIG. 12 . 
     The capture agent resulting from the process shown in  FIG. 11  can be used as a sensor device, because the binding of a hapten would “freeze” the relative orientations of the bound IgGs (whose interdomain connections are otherwise quite flexible), an effect that can be detected using a variety of biophysical methods such as fluorescence resonance energy transfer FRET (http://en.wikipedia.org/wiki/Fluorescence_resonance_energy_transfer) or other methods. Because the single-chain C3 nodes shown in  FIG. 11  incorporate terminal orienting His-tags, the structures are readily immobilized on, for example, Ni-resins, coated metal surfaces, or self-assembling membrane (SAM) surfaces that incorporate a Ni-chelating lipid Ni-NTA-DOGA (Ni-2-(bis-carboxymethyl-amino)-6[2-(1,3)-di-O-oleyl-glyceroxy)-acetyl-amino] hexanoic acid). 
     Examples of nanostructures functionalized with either one or two different IgG molecules that can be constructed using the basic component system are illustrated in  FIG. 12 .  FIG. 12   a  schematically recapitulates the assembly whose construction was outlined in  FIG. 11 .  FIGS. 12   b ,c show assemblies built on C3 and C4 nodes respectively. Construction of such assemblies can proceed via the initial immobilization of the central C3 or C4 nodes through their terminal His-tags, followed by attachment of Streptavipol:IgG conjugates, and subsequently, attachment of single-chain C3 nodes incorporating IgG binding domains, from which the terminal His-tags have first been removed.  FIG. 12   d  shows a hexagonal structure composed of Streptavipol:IgG conjugates and single-chain C3 nodes incorporating IgG binding domains.  FIG. 12   e  shows a square 2D lattice constructed of Streptavipol:IgG conjugates and C4-symmetric nodes. The assembly of structures such as those shown in  FIGS. 12   e,f  can be approached using “pH-annealable” iminobiotin conjugated nodes, linked through their terminal His-tags to the Ni-chelating lipid Ni-NTA-DOGA, and free to undergo 2-dimensional diffusion on a SAM surface.  FIG. 12   f  shows alternative schematic representations of the Streptavipol:IgG conjugate and C3 single-chain IgG conjugate modules. 
     A flexible set of nanoassembly components and modules can allow the construction of functionalized lattice structures, such as those illustrated in  FIG. 12 . This can enable new functional applications. Some applications of this technology are using the components to facilitate the assembly of diagnostic devices and sensors incorporating multiple molecular detectors whose relative geometry and stoichiometry are precisely controlled. An advantage of such structures is that they potentially offer much greater detection sensitivity and specificity than a detection system incorporating a single antibody (or single-chain Fv, etc.), because two different antibodies can be geometrically constrained, so that they potentially interact with the same antigen simultaneously. Thus, detection sensitivity and specificity can be improved, which can be useful for protein marker diagnostics. 
     Applications for nanocomponents as presented herein include biomedical diagnostics, proteomics and nanotechnology, including, for example, “personalized” approaches to medicine based on the analysis of specific disease-related protein biomarkers. This technology can enable advancement in the protein biomarker space, for example, with biosensor applications, such as those outlined in  FIG. 12 . The components can “snap” together to form functionalized structures like those shown in  FIG. 12 . These protein components can be used for nanodevice fabrication, for example, protein-based nanostructures for large-scale applications such as active membranes for water purification. 
     A substantially Cn-symmetric protein structure or node can include a protein structure or node which, for the most part, exhibits Cn-rotational symmetry, although a few atoms, groups of atoms, or amino acid residues may differ from the symmetric scheme. For example, the C3 and C4 symmetric nodes formed of single chains in  FIG. 4  can be considered to be substantially C3 and C4 symmetric, respectively, even though some subunits of a given node may differ from other subunits of that node, in that some subunits have biotins linked to their exterior surface whereas other subunits do not have biotins linked to their exterior surface. 
     A subunit of a protein node can include a group of amino acid residues that are closely associated with each other, for example, in spatial proximity and/or through intermolecular and/or interatomic forces, such as covalent bonds, disulfide bridges, electrostatic forces, hydrophobic forces, and/or van der Waals forces. A given subunit can have tertiary protein structure. Several subunits can aggregate to form a protein node having quaternary protein structure. The subunits that form a node can associate with each other through noncovalent forces, e.g., electrostatic forces, hydrophobic forces, and/or van der Waals forces, to form the node. Two or more subunits that form a node may or may not be covalently linked to each other, e.g., through polymeric or oligomeric amino acid chains. 
     “Linked” and “bound” can refer, for example, to an association of a molecule, a portion of a molecule, a group of atoms, or an atom with another molecule, portion of a molecule, group of atoms, or atom. The “linked” or “bound” state can arise from covalent, ionic, hydrophobic, van der Waals, or other types of interactions or forces. 
     A “subunit” can refer, for example, to a portion of a molecule, or a portion of a multimeric structure. 
     This application claims the benefit of U.S. Provisional Application No. 61/177,256, filed May 11, 2009, the specification of which is hereby incorporated by reference in its entirety. 
     The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. All examples presented are representative and non-limiting. The above- described embodiments of the invention may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described. 
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