The study of the adductor muscle-shell interface structure in three Mollusc species

The adductor muscle scar (AMS) is the fixation point of adductor muscle to the shell. It is an important organic inorganic interface and stress distribution area. Despite recent advances, our understanding of the structure and composition of the AMS remain limited. Here, we report study on the AMS of three bivalves: Mytilus coruscus, Chlamys farreri and Ruditapes philippinarum. Results showed that there were significant differences among their AMS structures. Both M. coruscus and C. farreri were found to have a columnar layer above the nacreous platelet shell structure at the AMS and this layer was more organized in M. coruscus. There was no distinguishable two layer structure in R. philippinarum. Atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FT-IR) results showed that the AMS was much smoother than the nacreous inner shell in all the three species and the AMS had minor different compositions from the nacreous shell layer. SDS-PAGE (sodium dodecyl-sulfate polyacrylamide gel electophoresis) study of the proteins isolated from the interface indicated that there was a 70 kappa Da protein which seemed to be specifically located to the highly organized columnar AMS structure in Mytilus coruscus. Further analysis of this protein showed it contained high level of Asx (Asp+Asn), Glx (Glu+Gln) and Gly. The special structure and composition of the AMS might play important roles in the stability, adhesion and function at this stress distribution site.