CONSPECTUS The uniquely diverse structures and functions of proteins offer many exciting opportunities for creating new materials with advanced properties. Exploiting these capabilities requires a set of versatile chemical reactions that can attach nonnatural groups to specific locations on protein surfaces. Over the years, we and others have developed a series of new techniques for protein bioconjugation, with a particular emphasis on achieving high site selectivity and yield. Using these reactions, we have been able to prepare a number of new materials with functions that depend on both the natural and the synthetic components. In this Account, we discuss our progress in protein bioconjugation over the past decade, focusing on three distinct projects. We first consider our work to harness sunlight artificially by mimicking features of the photosynthetic apparatus, with its beautifully integrated system of chromophores, electron transfer groups, and catalytic centers. Central to these photosystems are light-harvesting antennae having hundreds of precisely aligned chromophores with positions that are dictated by the proteins within the arrays. Our approach to generating similar arrangements involves the self-assembly of tobacco mosaic virus coat proteins bearing synthetic chromophore groups. These systems offer efficient light collection, are easy to prepare, and can be used to build complex photocatalytic systems through the modification of multiple sites on the protein surfaces. We then discuss protein-based carriers that can deliver drugs and imaging agents to diseased tissues. The nanoscale agents we have built for this purpose are based on the hollow protein shell of bacteriophage MS2. These 27 nm capsids have 32 pores, which allow the entry of relatively large organic molecules into the protein shell without requiring disassembly. Our group has developed a series of chemical strategies that can install dyes, radiolabels, MRI contrast agents, and anti-cancer drugs on the inside surface of these capsids. We have also developed methods to decorate the external surfaces with binders for specific proteins on cancer cells. As a third research area, our group has developed protein–polymer hybrid materials for water remediation. To reduce the toxicity of heavy metals in living cells, Nature has evolved metallothioneins, which are sulfur-rich polypeptides that bind mercury, cadmium, and other toxic ions at sub-parts-per-billion concentrations. Unfortunately, these proteins are very difficult to incorporate into polymers, largely because typical protein modification reactions target the very cysteine, lysine, and carboxylate-containing residues that are required for their proper function. To address this challenge, we developed a new way to attach these (and many other) proteins to polymer chains by expressing them as part of an N- and C-terminal modification “cassette.” The resulting materials retain their selectivity and can remove trace amounts of toxic metal ions from ocean water. Each of these examples has pres...

The controlled attachment of synthetic groups to proteins is important for a number of fields, including therapeutics, where antibody-drug conjugates are an emerging area of biologic medicines. We have previously reported a site-specific protein modification method using a transamination reaction that chemoselectively oxidizes the N-terminal amine of a polypeptide chain to a ketone or an aldehyde group. The newly introduced carbonyl can be used for conjugation to a synthetic group in one location through the formation of an oxime or a hydrazone linkage. To expand the scope of this reaction, we have used a combinatorial peptide library screening platform as a method to explore new transamination reagents while simultaneously identifying their optimal N-terminal sequences. N-methylpyridinium-4-carboxaldehyde benzenesulfonate salt (Rapoport's salt, RS) was identified as a highly effective transamination reagent when paired with glutamate-terminal peptides and proteins. This finding establishes RS as a transamination reagent that is particularly well suited for antibody modification. Using a known therapeutic antibody, herceptin, it was demonstrated that RS can be used to modify the heavy chains of the wild type antibody, or both the heavy and the light chains after N-terminal sequence mutation to add glutamate residues.

A series of self-assembling multidomain peptides have been designed, synthesized, and tested for their ability to individually suspend single-walled carbon nanotubes (SWCNTs) in water while preserving strong near-IR nanotube luminescence. Photometric and spectral measurements on individual SWCNTs revealed that emission in the common biocompatible coating agents Pluronic F127, ss-DNA, and BSA is approximately an order of magnitude weaker than in the bio-incompatible ionic surfactant SDBS. By contrast, one of the engineered peptides gave SWCNT emission ~40% as intense as in SDBS. A strong inverse correlation was also found between the spectral line widths of coated SWCNTs and the efficiency of their emission. Peptides with rationally designed selfassembly properties appear to be promising coatings that may enable SWCNT optical sensing applications in biological environments.