Photocleavable approaches to reversible bioconjugation
Mangubat-Medina, Alicia E
Ball, Zachary T
Doctor of Philosophy
The folding of peptides and proteins depends on the structural conformation of the amide backbone. Historically, side-chain modifications that respond to external stimuli, such as light, were a convenient technique for controlling folding and activity. As our curiosity into complex biological systems matures, so must the techniques used to probe these systems. While thoroughly less reported than light-sensitive side-chain modifications (called photocages), light-responsive modifications to the amide backbone structure represents a direct and powerful alternative to impact structural conformation. Using a copper-mediated, histidine-directed peptide backbone modification with vinyl boronic acids, it was possible to insert a traceless photocage into the N-H bond of the amide backbone. Several obstacles required addressing in order to achieve a traceless backbone photocage: first, the bond formed required a previously unreported photocleavage between C(sp2) and N atoms. Second, the photocaging reagents must maintain a minimum level of solubility in an aqueous solution. Finally, for maximized general use in biological systems, light-induce uncaging would ideally occur using visible light and near infrared light. Here, the first peptide backbone photocaging reagents are described. These represent a new class of photocaging reagents capable of tracelessly uncaging peptides using ultraviolet, blue, and near-IR light; reversibly disrupting peptide folding; reversibly interrupting enzymatic recognition of a peptide substrate; and reversibly modifying a model protein. These results represent a jumping point to developing a vast array of backbone photocages, optimized for a wide variety of contexts.