A dynamic biointerface in mussels mediated by a mechanoresponsive intermediate filament-based biopolymer

Mussels fabricate a distinctive biointerface that bridges their non-living biopolymeric byssus (used for anchoring in seashore habitats) with their soft-living tissue. Occurring in a region known as the byssus stem root, this biointerface is at once strong, yet also capable of on-demand release under apparent neurobiological control by the mussel, but this is not well understood. Here, we identify and sequence a previously unknown intermediate filament protein (MSP-1) that based on immunohistochemical staining and spectroscopic mapping comprises the surface of the stem root in direct contact with billions of motile cilia emerging from the living tissue. Further structural analysis indicates that MSP-1 is secreted as an α-helical coiled-coil but is mechanically converted subsequently to a β-sheet conformation. We posit that this mechanoresponsive conversion has a mechanical function in toughening the interface, but possibly also as a mechanosensory mechanism given its intimate contact with cilia in the living tissue.