Formation and Function of Metal Coordination Cross-Linking in Mytilus Mussel Byssus

Metals in biology are typically associated with physiological roles, but more recently there is evidence that some organisms use metal coordination cross-linking as a means of enhancing the properties of the materials they produce. The mussel byssus is the most prominent example of this materials fabrication approach, and there is strong evidence that mussels use metal cross-links harnessing the amino acids histidine and DOPA to yield exceptional properties including high toughness, self-healing capacity, unusual combinations of hardness and extensibility, and most prominently, underwater adhesion. In the first half of this chapter, we review the strong evidence for the role of protein-metal coordination in the formation and function of the mussel byssus. Yet currently, there is little understanding of exactly how these metals come to be found in the byssus in the first place. Thus, in the second half of the chapter, we review literature pertaining to metal uptake by mussels arising from the long-standing Mussel Watch Program originated by the NOAA in the 1970s that used Mytilus mussels as a biomarker for heavy metal pollution in ocean bodies. Combined with several newer findings focused on byssus biofabrication, this literature points to an intricate mechanism of metal acquisition, uptake, and incorporation into the byssus, providing interesting new avenues for research into this compelling topic, which has relevance for design and fabrication of bio-inspired metallopolymeric materials.