A molecular, morphometric and mechanical comparison of the structural elements of byssus from Mytilus edulis and Mytilus galloprovincialis.

Marine mussels are renowned for their ability to produce an extra-organismic tendon-like structure that can withstand the wave forces associated with the intertidal habitat. Initial characterization of byssal properties has focused on Mytilus edulis, with few detailed comparisons with other mussels. M. galloprovincialis, a closely related species, provides an opportunity for a thorough comparison. Three full-length cDNA clones encoding the byssal collagens, precollagen D (preCol-D), preCol-NG and preCol-P, were isolated from M. galloprovincialis. Comparisons with M. edulis preCol-D, preCol-NG and preCol-P reveal a 91.3 %, 88.6 % and 90.1 % identity with the cDNA and an 89.0 %, 88.1 % and 89.0 % identity with the deduced protein sequences, respectively. Key elements are maintained between the species: in particular, modeled bends in the collagen helix due to breaks in the Gly-X-Y pattern and the location of cysteine and putative 3,4-dihydroxyphenylalanine (DOPA) residues. A potentially important difference between the two is that, in all cases, M. galloprovincialis byssal collagens contain additional histidine residues in their flanking domains. The significance of this may lie in the ability of M. galloprovincialis to utilize more metal chelate cross-links, which have been implicated in byssal thread stability. M. edulis threads are typically twice the length and diameter of M. galloprovincialis threads and appear to contain nearly 10 % more collagen. These differences are maintained even when the different thread portions are compared. Despite differences in a number of parameters, most notably that whole M. galloprovincialis threads are stiffer, threads whether whole or separated into proximal and distal portions, have similar mechanical behaviors. It is apparent from this comparison that M. galloprovincialis and M. edulis are seemingly interchangeable models for byssal research.