Materials scientists increasingly draw inspiration from the study of how biological systems fabricate materials under mild synthetic conditions by using self‐assembled macromolecular templates. Containerlike protein architectures such as viral capsids and ferritin are examples of such biological templates. These protein cages have three distinct interfaces that can be synthetically exploited: the interior, the exterior, and the interface between subunits. The subunits that comprise the building blocks of these structures can be modified both chemically and genetically in order to impart designed functionality to different surfaces of the cage. Therefore, the cages possess a great deal of synthetic flexibility, which allows for the introduction of multifunctionality in a single cage. In addition, hierarchical assembly of the functionalized cages paves the way for development of a new class of materials with a wide range of applications from electronics to biomedicine.

Viruses and virus-like particles (VLPs) are useful tools in biomedical research. Their defined structural attributes make them attractive platforms for engineered interactions over large molecular surface areas. In this report, we describe the use of VLPs as multivalent macroinitiators for atom transfer radical polymerization (ATRP). The introduction of chemically reactive monomers during polymerization provides a robust platform for post-synthetic modification via the copper-catalyzed azide-alkyne cycloaddition reaction. These results provide the basis to construct nanoparticle delivery vehicles and imaging agents using protein-polymer conjugates.

No abstract

Icosahedral nontailed double-stranded DNA (dsDNA) viruses are present in all three domains of life, leading to speculation about a common viral ancestor that predates the divergence of Eukarya, Bacteria, and Archaea. This suggestion is supported by the shared general architecture of this group of viruses and the common fold of their major capsid protein. However, limited information on the diversity and replication of archaeal viruses, in general, has hampered further analysis. Sulfolobus turreted icosahedral virus (STIV), isolated from a hot spring in Yellowstone National Park, was the first icosahedral virus with an archaeal host to be described. Here we present a detailed characterization of the components forming this unusual virus. Using a proteomics-based approach, we identified nine viral and two host proteins from purified STIV particles. Interestingly, one of the viral proteins originates from a reading frame lacking a consensus start site. The major capsid protein (B345) was found to be glycosylated, implying a strong similarity to proteins from other dsDNA viruses. Sequence analysis and structural predication of virion-associated viral proteins suggest that they may have roles in DNA packaging, penton formation, and protein-protein interaction. The presence of an internal lipid layer containing acidic tetraether lipids has also been confirmed. The previously presented structural models in conjunction with the protein, lipid, and carbohydrate information reported here reveal that STIV is strikingly similar to viruses associated with the Bacteria and Eukarya domains of life, further strengthening the hypothesis for a common ancestor of this group of dsDNA viruses from all domains of life.In comparison to viruses with eukaryotic and bacterial hosts, little is known about the viruses that infect Archaea. This is due, in part, to the relatively recent delineation of the archaeal domain of life but, more significantly, to the challenges of isolating and culturing the host organisms (42). The extreme environments favored by many archaeal species and limited knowledge about their biochemistry and biology exacerbate this problem. Often, it is through the study of host-virus interactions that insights to the biology of the host are elucidated. The recent discovery of Sulfolobus turreted icosahedral virus (STIV) presents an opportunity to expand our knowledge of virology, study host biology, and investigate the evolutionary relationship of viruses from all three domains of life. Studies on the structure of STIV have revealed similarities with prokaryotic and eukaryotic viruses that suggest a common ancestry for icosahedral double-stranded DNA (dsDNA) viruses (30, 38).STIV was isolated from Sulfolobus enrichment cultures that were established from a high-temperature acidic hot spring (ϳ80°C, pH ϳ3) in Yellowstone National Park (38). The virus was subsequently shown to infect virus-free isolates of Sulfolobus solfataricus strain P2, for which the complete genome has been sequenced. The electron cryomicroscopy (cry...

The antitumor agent doxorubicin was covalently bound and selectively released in a pH dependent manner from the interior surface of a genetically modified small heat shock protein (Hsp) cage.

Protein cages, including viral capsids, ferritins, and heat shock proteins (Hsps), can serve as nanocontainers for biomedical applications. They are genetically and chemically malleable platforms, with potential as therapeutic and imaging agent delivery systems. Here, both genetic and chemical strategies were used to impart cell-specific targeting to the Hsp cage from Methanococcus jannaschii. A tumor vasculature targeting peptide was incorporated onto the exterior surface of the Hsp cage. This protein cage bound to alpha(v)beta(3) integrin-expressing cells. Cellular tropism was also imparted by conjugating anti-CD4 antibodies to the exterior of Hsp cages. These Ab-Hsp cage conjugates specifically bound to CD4(+) cells. Protein cages have the potential to simultaneously incorporate multiple functionalities, including cell-specific targeting, imaging, and therapeutic agent delivery. We demonstrate the simultaneous incorporation of two functionalities, imaging and cell-specific targeting, onto the Hsp protein cage.

Viral capsids have the potential for combined cell/tissue targeting, drug delivery, and imaging. Described here is the development of a viral capsid as an efficient and potentially relevant MRI contrast agent. Two approaches are outlined to fuse high affinity Gd 3؉ chelating moieties to the surface of the cowpea chlorotic mottle virus (CCMV) capsid. In the first approach, a metal binding peptide has been genetically engineered into the subunit of CCMV. In a second approach gadolinium-tetraazacyclododecane tetraacetic acid (GdDOTA) was attached to CCMV by reactions with endogenous lysine residues on the surface of the viral capsid. T 1 and T 2 ionic relaxivity rates for the genetic fusion particle were R1 MRI is one of the most utilized imaging techniques in medicine since it is noninvasive and provides comparatively high-resolution information. The usefulness of the technique is augmented by the use of contrast agents that increase the rate of water proton relaxation and can therefore increase contrast between tissues. Gadolinium (Gd 3ϩ ) chelates are commonly used as contrast agents in clinical settings (1,2). In general, there are two ways to improve the imaging sensitivity using contrast agents: either by increasing the relaxivity of water protons through direct interaction with the contrast agent or by targeted delivery of the agent to specific locations within the body.Viral capsids are multimeric protein assemblies that form cage architectures and can be generally categorized as protein cages. Other, nonviral protein cages include heat shock proteins, ferritins, and vault ribonucleoprotein particles, among others. These protein cages can serve as robust synthetic platforms that are chemically and genetically malleable and can be readily modified. Previous studies have explored the use of protein cages as therapeutic or imaging delivery agents (3-5). Cell targeting has been achieved by utilizing capsids with natural affinities for cellular receptors or by chemically linking peptides or antibodies to protein cage architectures (6,7). In addition, targeted protein cages incorporating a therapeutic payload (doxorubicin) have been constructed, demonstrating the multifunctional capacity for biomedical applications (8).Protein cages and more specifically viral capsids, have the potential to serve as extremely efficient contrast agents for the following reasons: 1) viral capsids are large, commonly between 18 -100 nm in diameter, and relatively rigid molecular structures with large rotational correlation times, resulting in increased relaxivity rates; 2) viral capsids can serve as robust platforms onto which multiple functional motifs can be added through genetic or chemical modifications (9 -16). These modifications could potentially result in the attachment of both Gd 3ϩ binding and site-specific targeting functionalities; and 3) viral capsids can potentially carry hundreds (if not thousands) of Gd 3ϩ ions and the contrast from an individual capsid will increase significantly with the number of Gd 3ϩ ions it car...

A goal of biomimetic chemistry is to use the hierarchical architecture inherent in biological systems to guide the synthesis of functional three dimensional structures. Viruses and other highly symmetrical protein cage architectures provide defined scaffolds to initiate hierarchical structure assembly. Here we demonstrate that a crosslinked branched polymer can be initiated and synthesized within the interior cavity of a protein cage architecture. Creating this polymer network allows for the spatial control of pendant reactive sites and dramatically increases the stability of the cage architecture. This material was generated by the sequential coupling of multifunctional monomers using click chemistry to create a branched crosslinked polymer network. Analysis of polymer growth by mass spectrometry demonstrated that the polymer was initiated at the interior surface of the cage at genetically introduced cysteine reactive sites. The polymer grew as expected to generation 2.5 where it was limited by the size constraints of the cavity. The polymer network was fully crosslinked across protein subunits that make up the cage and extended the thermal stability for the cage to at least 120°C. The introduced reactive centers were shown to be active and their number density increased with increasing generation. This synthetic approach provides a new avenue for creating defined polymer networks, spatially constrained by a biological template.