Purification of DOPA-Containing Foot Proteins from Green Mussel, Perna viridis, and Adhesive Properties of Synthetic Model Copolypeptides

The thread-like adhesive tissue of the green mussel, Perna viridis, is referred to as the byssus. The phenol gland-derived proteins are involved in the underwater adhesion of the byssus. The objectives of the present study are identification and characterization of the phenol gland-derived proteins in the foot of P. viridis. P. viridis foot contains at least eight kinds of potential precursor proteins, designated as P. viridis foot proteins (Pvfp)-a to -h. Among the precursors, Pvfp-g and Pvfp-h are found at relatively high levels in the phenol gland. These proteins are considered to be essential components in the adhesive plaque, which mediates adhesion of the thread to the substrate surface. Both Pvfp-g and Pvfp-h are enriched in L--3,4-dihydroxyphenyl--alanine (DOPA), tyrosine (Tyr) and cysteine (Cys), as well as glycine (Gly) and lysine (Lys). According to the amino acid compositions in Pvfp-g and Pvfp-h, two copolypeptides containing four amino acids, Cys, Tyr, Gly, and Lys, were synthesized as the biomimetic model materials. The copolypeptides were subjected to the tyrosinase-catalyzed oxidation, followed by tensile shear strength test. The results suggest that DOPA and Cys in Pvfp-g and Pvfp-h cooperatively contribute to rapid protein cross-linking, enhancing the cohesive strength of the matrix of the adhesive plaque.