From byssal secretion to solidification: Unraveling the molecular interactions governing byssal thread mechanical properties in marine mussels

Marine organisms have evolved diverse strategies for underwater attachment. For instance, barnacles rely on cement for permanent fixation, whereas marine mussels achieve essential anchorage in marine environments through the secretion of byssal threads. This study focuses on the byssal solidification process in the mussel Mytilus coruscus , investigating the temporal changes in mechanical properties and the roles of protein disulfides and metal coordination bonds in this phase. We measured the byssal breaking force at various secretion time points and found it significantly increased within 12 h post-secretion, indicating a crucial period for solidification. To elucidate the underlying biochemical mechanisms, we disrupted cross-linking using DTT and EDTA during byssal solidification, targeting disulfide and metal coordination bonds, respectively. Disruption of disulfide and metal coordination bonds compromised byssal tensile strength (from 199.17 MPa in controls to 78.43 MPa with DTT and 163.70 MPa with EDTA), without altering thread diameter. The byssal breaking force was reversed by re-oxidation or Ca 2+ recovery, confirming the important role of molecular interactions during byssal thread solidification. Raman spectroscopy confirmed that DTT eliminated characteristic disulfide peaks (495–550 cm −1 ), whereas EDTA declined resonance bands associated with DOPA–metal (550 and 637 cm −1 ) and His–Zn 2+ coordination (1276 and 1601 cm −1 ). Furthermore, ICP-MS and XPS identified calcium as the predominant metal ion, and FTIR confirmed EDTA-induced protein conformational changes. This study provided the characterization of the byssal solidification timeline, defining the evolution of breaking force during the byssal solidification. It further elucidated the specific contributions of disulfide cross-links and metal coordination to the mechanical performance of the solidified byssus. These findings provided insights into the molecular interactions that support functional properties during byssal solidification. This study enhances the understanding of biochemical processes in byssus formation and its adaptation to marine environments, with a particular emphasis on the byssal solidification process.