Proteomic basis of mussel byssal adhesion: Substrate-specific expression of byssal proteins determines attachment...

Marine mussels secrete byssal threads to attach to substrates, although the adhesion strength varies significantly with the type of surface. This study investigated the adhesion of Mytilus coruscus (5.5 ± 0.2 cm) byssal plaques on steel, wood, and rope substrates (n = 20), revealing significantly higher adhesion strength on rope compared to wood and steel. A comparative proteomic analysis of byssal plaques, collected from substrates exhibiting the highest (rope) and lowest (steel) adhesion strengths, identified 309 differentially expressed proteins (DEPs) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). This analysis demonstrated that the adhesion differences stem primarily from variations in the relative abundance of key byssal proteins-including mussel foot proteins (e.g., Mfp3, Mfp6), collagen-like proteins (e.g., C1q domain-containing proteins), and enzymatic regulators (tyrosinase/TYR-C, peroxidase/BPLP-1, superoxide dismutase)-rather than compositional changes. The results indicate that Mfp3, a major adhesive protein, was more abundant on rope, which may explain the significantly higher adhesion strength of the byssal plaque on rope compared to steel. Specifically, the reduced abundance of C1q proteins on steel was associated with lower adhesion compared to the rope substrate. The dysregulation of enzymatic proteins (e.g., increased BPLP-1) suggests impaired DOPA metabolism and oxidative stress mitigation, contributing to diminished adhesive performance on steel relative to rope. Gene knockdown experiments confirmed the functional importance of BP-3, BPLP-1, and TYR-C expression in maintaining plaque adhesion force and plaque adhesion strength. These findings suggest that substrate-specific protein expression and abundance are key factors contributing to the variation in byssal adhesion strength. This highlights the complex interplay between substrate physicochemical properties and the molecular composition of the adhesive interface.