Amino acid chemistry and post-translational modifications underlying marine adhesive proteins: Biochemical insights for designing underwater adhesives.

Underwater adhesion remains a complex challenge due to the interference of water with traditional bonding mechanisms. Marine organisms, such as mussels, sandcastle worms, and barnacles, have evolved specialized adhesive proteins that overcome these limitations through functional amino acid motifs. This review highlights how post-translationally derived amino acid motifs, such as 3,4-dihydroxylphenylalanine (DOPA) and phosphoserine, drive interfacial adhesion and the curing process through interfacial binding, metal coordination, and crosslinking. Alongside these, canonical amino acids, such as cysteine, lysine, arginine, histidine, glycine, and proline, contribute to redox buffering, electrostatic interactions, structural flexibility, and fibrillar assembly, which are essential for adhesive structure. The adhesive strategies of mussels, sandcastle worms, and barnacles reflect diverse mechanisms: mussels utilize DOPA-rich proteins with redox-regulation; sandcastle worms employ electrostatically driven coacervation and ion-mediated curing; barnacles generate nanostructured networks stabilized by disulfide bonding and hydrophobic packing. This review presents a unified molecular framework that links amino acid chemistry, biochemical transformations, and structural integration in underwater adhesion. It further discusses synthetic and recombinant approaches that mimic these natural systems, including catechol-functionalized polymers, complex coacervate adhesives, and genetically engineered proteins. These biomimetic platforms demonstrate the potential of translating marine adhesion logic into robust, water-compatible materials for biomedical and industrial applications.