A multi-tasking polypeptide from bloodworm jaws: Catalyst, template, and copolymer in film formation

Bloodworm jaws are composites of protein, melanin, and both mineral and ionic copper. To date, nanomechanical tests have correlated the ionic copper and melanin with hardness and wear resistance, but the function of protein is uncertain. Here, we characterize a Gly- and His-rich protein called multi-tasking protein (MTP) and, using recombinant protein, show that it performs six distinct functions critical for jaw formation and performance, namely (1) recruiting 22 equiv of Cu2+, (2) mediating a liquid-liquid phase separation of the MTP-copper complex, (3) catalyzing the oxidation of 3,4-dihydroxyphenylalanine (Dopa) to melanin, (4) templating the interfacial polymerization of melanin, (5) integrating melanin and itself into thin films and fibers, and (6) providing intermolecular cohesion through Cu bridging. MTP achieves all these by assuming unprecedented roles as a building block, organizer, and fabricator—a processing feat of considerable relevance to the autonomous production of other polymer composites, blends, and/or networks.