Rational design of self-assembly of proteins, which plays pivotal roles in biology, is an important subject for biotechnology and also bottom-up nanotechnology. This paper has proposed a novel strategy for construction of artificial peptide-nanospheres by self-assembly. Mimicking formation of spherical viruses and clathrin, we designed a novel C3-symmetric peptide conjugate bearing three beta-sheet-forming peptides. These peptide conjugates formed antiparallel beta-structures and self-assembled into nanospheres with the size of about 20 nm in the acidic solution.

Natural plant viruses are rodlike or spherical nanoassemblies with discrete size and morphology, in which genome nucleic acids are encapsulated by self-assembled coat proteins (capsids). Most capsids in spherical viruses have an icosahedral symmetry and the number and arrangement of subunits are related to the triangulation number (T number), which is derived from quasi-equivalence theory.[1] For example, tomato bushy stunt virus (TBSV, T = 3) consists of 180 quasi-equivalent protein subunits that comprise 388 amino acids each (diameter of capsid ca. 33 nm). [2] Recently, the application of bacteriophages such as M13 phage [3] and plant viruses [4] such as tobacco mosaic virus (TMV), [5] cowpea mosaic virus (CPMV), [6] and cowpea chlorotic mottle virus (CCMV) [7] in nanotechnology have attracted much attention because of their fascinating nanostructures with a discrete nanospace. Virus nanotechnologies depend on the structure of "ready-made" capsids, however, the chemical strategy of de novo designed "tailor-made" viruslike nanocapsules is still in its infancy. The development of designed capsid molecules for the reconstruction of viral architectures would enhance the potential of viruslike nanocapsules and notably contribute to advance nanobioscience. To date, virus-inspired nanocapsules with a size of about 1-5 nm have been self-assembled by hydrogen bonds [8] and coordination bonds. [9] However, the size of these supramolecular nanocapsules is evidently smaller than that of natural viruses, and consequently their applications have been limited to the inclusion of small guest molecules. Yeates and coworkers have developed a general strategy for the construction of protein architectures, such as cages and filaments, by the use of fusion proteins.[10] We have demonstrated that virus-inspired C 3 -symmetric b-sheet-forming peptide conjugates self-assemble into nanocapsules [11a,c] and nanofibers. [11b,c] Recently, we have also reported that C 3 -symmetric glutathione conjugates self-assemble into nanospheres.[11d, e]Herein we show a first example of a synthetic viral capsid self-assembled from a 24-mer b-annulus peptide (1: INHVGGTGGAIMAPVAVTRQLVGS) in water ( Figure 1). The b-annulus peptide motif (Ile69-Ser92) in the TBSV capsid participates in the formation of a dodecahedral internal skeleton, [2b] thus we expected that the peptide 1 Figure 1. Illustration of the hypothesized formation of viruslike nanocapsules by self-assembly of 24-mer b-annulus peptide 1.

Glycosylated poly(phenyl isocyanide)s were synthesized in an attempt to elucidate the effect of three-dimensionally regulated saccharide arrays along highly stereoregular polymer backbones on molecular recognition. Poly(phenyl isocyanide)s substituted with α-d-glucose, β- d -glucose, β- d -galactose, and β-lactose were obtained by polymerization of the corresponding acetylated glycosyl phenyl isocyanides with a Ni(II) catalyst and subsequent deacetylation. Helical main chains and spatially regulated saccharide arrays of the poly(phenyl isocyanide)s were demonstrated by CD spectroscopy and molecular dynamics calculations. Their binding affinity with lectins was investigated by inhibition of hemagglutination and fluorescence spectroscopy. The rigid cylindrical phenyl isocyanide glycopolymers exhibited little specific interactions with lectins, which was in contrast to the highly specific interactions of the multivalent glycoclusters along flexible phenylacrylamide glycopolymers. It has been demonstrated that the compatibility of orientation and spacing of clustered saccharide chains of glycopolymers is essential for specific molecular recognition by lectin.

This feature article describes recent progress in synthetic strategies to construct viral capsid-like spherical nanomaterials using the self-assembly of peptides and/or proteins. By mimicking the self-assembly of spherical viral capsids and clathrin, trigonal peptide conjugates bearing β-sheet-forming peptides, glutathiones, or coiled-coil-forming peptides were developed to construct viral capsid-like particles. β-Annulus peptides from tomato bushy stunt virus self-assembled into viral capsid-like nanocapsules with a size of 30-50 nm, which could encapsulate various guest molecules and be decorated with different molecules on their surface. Rationally designed fusion proteins bearing symmetric assembling units afforded precise viral capsid-like polyhedral assemblies. These synthetic approaches to construct artificial viruses could become useful guidelines to develop novel drug carriers, vaccine platforms, nanotemplates and nanoreactors.