Principal Investigator Ronald Raines
By exploiting the fundamental basis for the stability of collagen (which is the most abundant protein in humans), we are creating new materials to detect and treat wounds, tumors, and other abnormalities. For 25 years, the prevailing paradigm had been that the enhanced stability from the post-translational modification of collagen by the enzyme prolyl 4-hydroxylase arises from water molecules that form bridges between the hydroxyl group of (2S,4R)-4-hydroxyproline (Hyp) residues and a main-chain oxygen. We recognized that the hydroxyl group could instead have stereoelectronic consequences that stabilize the desired conformation. To test this hypothesis, we synthesized collagen chains in which (2S,4R)-4-fluoroproline residues replace Hyp. These chains form triple helices of extraordinary stability, despite the inability of organic fluorine to form strong hydrogen bonds. In contrast, the diastereomeric (2S,4S)-4-fluoroproline was highly destabilizing. These data were the first to demonstrate that a stereoelectronic effect can stabilize a protein structure. We replicated the stereoelectronic effects with reciprocal steric effects (e.g., using 4‑methylproline residues), ultimately creating the most stable known triple helix. We are now translating our knowledge into a preclinical context, and have shown that collagen mimetic peptides containing 4‑fluoroproline residues can anneal to damaged collagen, forming a tight, noncovalent interaction. We are exploiting this peptidic “pylon” to anchor molecules in damaged collagen, providing a new modality for the diagnosis and treatment of wounds in a variety of contexts, including near tumors. In addition, we are developing potent, selective, and bioavailable prolyl 4‑hydroxylase inhibitors, which have promise as antifibrotic and antimetastatic agents.