pH-Responsive Self-Organization of Metal-Binding Protein Motifs from Biomolecular Junctions in Mussel Byssus

Mussels rapidly fabricate tough and self-healing biopolymeric fibers called byssal threads that provide an excellent role model for bio-inspired design. The remarkable tensile properties arise from a collagenous protein family known as preCols, which self-assemble into a semicrystalline array in the distal thread core. Histidine-rich domains (HRDs) at the preCol ends are critical both for the self-healing capacity and for the thread assembly process due to their propensity for coordinating transition metal ions; however, very little is understood about the molecular relationship between HRD sequence, structure, and function. Here, a comprehensive spectroscopic investigation of two model peptides based on conserved repetitive motifs in the HRDs is performed to elucidate molecular level details of their role in thread assembly and function. It is observed that environmental factors relevant to the natural assembly process (e.g., concentration, pH, and metal content) trigger dramatic changes in HRD nanostructure and higher order assembly, leading to the formation of highly defined backbone conformation and metal binding geometry.