Protein cages viruses

Douglas, T. and Young, M. (1998) Host-guest encapsulation of materials by assembled virus protein cages. Nature, 393, 152-155. 

To test the dominance of electrostatic effects in the mineralization model, a mutant of CCMV was constructed (subE) in which all the basic residues on the N-terminus of the coat protein were substituted for glutamic acid (E), thus dramatically altering the electrostatic character of the interior of the assembled protein cage." This mutant was able to catalyze the oxidative hydrolysis of Fe(II) to form an iron oxide nanoparticle encapsulated within the protein cage of the modified virus. High-rcsolution spectral imaging allowed the elemental composition of a protein-mineral composite material to be resolved (1 nm spatial resolution, Fig. 3). This clearly showed that the mineral nanoparticle was completely encapsulated within the protein cage structure. This mutant is able to bind Fe(lT), facilitate its autoxidation... 

Synthetic self-assembled scaffolds allow for development of biomimetics that have tailored stabilities and sizes. Peptides have the advantages of inherent biocompatibility and of remarkable diversity regarding functionality and ligand orientations. The virus scaffolds have natural self-assembly features for protein cages in a wide variety of sizes and architectures. 

The second category of the viral templates discussed here are spheroidal plant viruses, most of which have icosahedral symmetry. In this section, we first describe the fundamental characteristics of two representative viruses that have been widely enlisted cowpea mosaic virus (CPMV) and CCMV. We then discuss endeavors to functionalize the surfaces of these viral nanoparticles by both chemical and genetic modifications that mirror the ones utilized for TMV. Finally, efforts to harness a range of inner cavity sizes, perhaps the most unique feature of this class of viral assemblies, from various spheroidal viruses and protein cages for the synthesis of precisely controlled nanoparticles are described. 

One particular asset of structured self-assemblies is their ability to create nano- to microsized domains, snch as cavities, that could be exploited for chemical synthesis and catalysis. Many kinds of organized self-assemblies have been proved to act as efficient nanoreactors, and several chapters of this book discnss some of them such as small discrete supramolecular vessels (Chapter Reactivity In Nanoscale Vessels, Supramolecular Reactivity), dendrimers (Chapter Supramolecular Dendrlmer Chemistry, Soft Matter), or protein cages and virus capsids (Chapter Viruses as Self-Assembled Templates, Self-Processes). In this chapter, we focus on larger and softer self-assembled structures such as micelles, vesicles, liquid crystals (LCs), or gels, which are made of surfactants, block copolymers, or amphiphilic peptides. In addition, only the systems that present a high kinetic lability (i.e., dynamic) of their aggregated building blocks are considered more static objects such as most of polymersomes and molecularly imprinted polymers are discussed elsewhere (Chapters Assembly of Block Copolymers and Molecularly Imprinted Polymers, Soft Matter, respectively). Finally, for each of these dynamic systems, we describe their functional properties with respect to their potential for the promotion and catalysis of molecular and biomolecu-lar transformations, polymerization, self-replication, metal colloid formation, and mineralization processes. 

Figure 1.5 (a) Cryoelectron microscopy reconstruction of icosahedral symmetry of Sulfolobus turreted virus (b) Three interfaces within a protein cage available for modification. Reproduced with permission from Ref [36] 2007, Wiley-VCH Verlag GmbH Co. KGaA. 

Ren, Y., Wong, S.M., Lim, L.Y., 2007. Folic acid-conjugated protein cages of a plant virus a novel delivery platform for doxorubicin. Bioconjug. Chem. 18, 836-843. 

Although the systems described here have not been used for nanoencapsulated cascade reactions, or of course, for mutually incompatible catalysts, they offer an attractive possibility for the extension of this field, especially given the availability of a wide range of protein-based nanometer-sized cages, such as chaperonins, DNA binding proteins, and the extensive class of viruses [107]. 

Icosahedral capsid viruses and clathrins are examples of coat proteins of which there are many. Another example that has been extensively studied is coat protein II, or COPII, which is composed of an inner cage and outer coat [5], The inner cage is a cuboctahedron approximately 60 nm across. It has square and triangular faces which can only be constructed if four protein strands emanate from the structure s hub, rather than the three seen in clathrins. It also transpires that the proteins interact with each other at the vertices without any of the extensive interdigitation seen in clathrin cages. 

The ISCOM is a cage-like 30-40 nm particle formed through hydrophobic interactions between amphipathic molecules and the complexes formed by Quillaja saponin, cholesterol and phospholipids such as phosphatidylcholine or ethanol-amine [8]. The amphipathic molecules are derived from cell walls and membranes from a variety of viruses, bacteria and parasites. The basic ISCOM which is formed in the absence of envelope protein is termed ISCOM matrix or empty ISCOM. The addition of phospholipids is necessary in order to provide a certain flexibility of the... 

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