Stiff Coatings on Compliant Biofibers: The Cuticle of Mytilus californianus Byssal Threads,

摘要

For lasting holdfast attachment, the mussel Mytilus californianus coats its byssal threads withna protective cuticle 2-5 μm thick that is 4-6 times stiffer than the underlying collagen fibers. Althoughncuticle hardness (0.1 GPa) and stiffness (2 GPa) resemble those observed in related mussels, a moreneffective dispersion of microdamage enables M. californianus byssal threads to sustain strains to almostn120% before cuticle rupture occurs. Underlying factors for the superior damage tolerance of the byssalncuticle were explored in its microarchitecture and in the cuticular protein, mcfp-1. Cuticle microstructurenwas distinctly granular, with granule diameters (∼200 nm) only a quarter of those in M. galloproVincialisncuticle, for example. Compared with homologous proteins in related mussel species, mcfp-1 from M.ncalifornianus had a similar mass (∼92 kDa) and number of tandemly repeated decapeptides, and containednthe same post-translational modifications, namely, trans-4-hydroxyproline, trans-2,3-cis-3,4-dihydroxyproline,nand 3,4-dihydroxyphenylalanine (Dopa). The prominence of isoleucine in mcfp-1, however,ndistinguished it from homologues in other species. The complete protein sequence deduced from cDNAsnfor two related variants revealed a highly conserved consensus decapeptide PKISYPPTYK that is repeatedn64 times and differs slightly from the consensus peptide (AKPSYPPTYK) of both M. galloproVincialisnand M. edulis proteins.