Nanoparticle-Templated Assembly of Viral Protein Cages

Abstract

Self-assembly of regular protein surfaces around nanoparticle templates provides a new class of hybrid biomaterials with potential applications in medical imaging and in bioanalytical sensing. We report here the first example of efficiently self-assembled virus-like particles (VLPs) having a brome mosaic virus protein coat and a functionalized gold core. The present study indicates that functionalized gold particles can initiate VLP assembly by mimicking the electrostatic behavior of the nucleic acid component of the native virus. These VLP constructs are symmetric, with the protein stoichiometry and packaging properties indicating similarity to the icosahedral packing of the capsid. Moreover, a pH-induced swelling transition of the VLPs is observed, in direct analogy to the native virus.Two-dimensional crystalline arrays of proteins self-assembled on flat supports have recently emerged as prime candidates for biotechnological applications. 1,2 Due to their intrinsic symmetry, these arrays can provide high density and equivalent environments for binding domains, characteristics that are difficult to achieve by any other technologies. 3 The ability to engineer specific regulatory switches into proteins by use of recombinant DNA technology also promises additional uses in these arrays.The protein coat, or capsid, of many viruses provides a discrete analogue to extended protein assemblies on planar surfaces. As a consequence, modified-virus capsids have been proposed as versatile biomolecular platforms for displaying engineered peptide sequences for triggering specific host responses. 3,4 Moreover, the regular motif of tubular or quasispherical capsids has been used for the templated synthesis of nanomaterials ranging from magnetic particles 5 to nanowires for electronic applications. 6 The majority of current studies on protein cage-based materials have focused on the use of the capsid surface as a nucleator and/or template for the growth or attachment of inorganic entities. The converse approach of using inorganic particles to nucleate viral capsids represents a new method for synthesizing hybrid inorganic/viral particles, thus widening the range of possible combinations of physical and chemical properties.Preliminary experiments on the encapsulation of functionalized gold nanoparticles into brome mosaic virus (BMV) capsids have shown that the VLP protein coat is likely organized in a closed shell, similar in its physicochemical properties to the native virus. 7,8 These previous examples of nanoparticle encapsidation were characterized by an extremely low yield relative to the formation of empty capsid (∼1%), 9 in stark contrast with the essentially quantitative in-vivo incorporation of the native RNA. 9 Practical application of these systems, however, requires a high yield of homogeneous material. Moreover, knowledge of the VLP shell structure and concomitant preservation of its functional attributes also requires homogeneous materials that can be used for high-resolution structural studies.The fact that...

Molecular protein adaptor with genetically encoded interaction sites guiding the hierarchical assembly of plasmonically active nanoparticle architectures

“…The most widely used biological template for directed AuNP assemblies is DNA 21,22 , but also peptide fibrils 23 or protein fibres 2 were deployed as templates, for example, amyloid fibres for the construction of conducting nanowires 2 . Another prominent example for proteinaceous assemblies is the patterning or encapsulation of metal NPs by virus capsids [24][25][26] . The great advantage of protein-based assemblies is the ability to store and tune information about precise structure, composition and interaction potential on the genetic level.…”

Core-controlled polymorphism in virus-like particles

“…metamaterials ͉ protein cage ͉ self-assembly ͉ surface plasmon ͉ virus assembly E ngineered virus capsids and protein cage structures have shown increasing promise as therapeutic and diagnostic vectors (1-6), imaging agents (7-10), and as templates and microreactors for advanced nanomaterials synthesis (11)(12)(13)(14)(15)(16)(17). Here, we address the rules for the formation of symmetric protein cages consisting of viral capsid subunits formed over a functionalized inorganic nanoparticle core, called virus-like particles (VLPs).VLPs provide an example of how biomimetic self-organization can combine the natural characteristics of virus capsids with the exquisite physical properties of nanoparticles (18)(19)(20). Interactions between the artificial cargo and the protein carrier affects both the self-assembly and the stability of the resulting structure, yet very little is known about them.…”

“…VLPs provide an example of how biomimetic self-organization can combine the natural characteristics of virus capsids with the exquisite physical properties of nanoparticles (18)(19)(20). Interactions between the artificial cargo and the protein carrier affects both the self-assembly and the stability of the resulting structure, yet very little is known about them.…”

“…We have determined that a gold core functionalized with a coating of carboxylated polyethylene glycol (PEG) can allow efficient assembly of VLPs (18). Here, we report some first steps in a systematic examination of how these cores influence the capsid structures and functional properties.…”

“…When gold particles are absent from the assembly mixture, a larger number of empty capsids are observed in TEM micrographs than in the presence of Au (18). Incorporation of gold nanoparticles is therefore the result of the competition between the formation of empty capsids and other aggregates and VLPs.…”