Development and Applications of N-terminal Protein Bioconjugation Reactions
With highly evolved structures and function, proteins have an extraordinarily diverse range of capabilities. In order to take advantage of their unparalleled specificity in the field of chemical biology, bioconjugation methods can be used to produce synthetically modified proteins. As applications for protein-based materials are becoming ever-increasingly complex, there is a constant need for methodologies that can covalently modify protein substrates. More specifically, there is a requirement for reliable and chemoselective reactions that result in well-defined bioconjugates that are modified in a single location. We have developed a protein transamination strategy that uses N-methylpyridinium-4-carboxaldehyde benzenesulfonate salt (Rapoport's salt) to oxidize the N-terminal amine to a ketone or aldehyde functionality. We have identified high-yielding conditions for this reaction, such as N-terminal sequence and pH, and shown its applicability in the modification of several protein systems. In addition, we have used N-terminal protein modification methodologies in the synthesis of protein-DNA conjugates, towards the goal of developing a generalizable DNA-directed protein immobilization platform. Overall, the work presented herein expands the toolkit of methodologies available for building protein-based materials.