Polyphosphoprotein from the adhesive pads of Mytilus edulis

Achieving a satisfactory biochemical explanation for the opportunistic unde rwater adhesion of marine invertebrates such as mussels and barnacles requi res a detailed characterization of proteins extracted from holdfast structu res produced by these, organisms. Mefp-5 is an adhesive protein derived fro m the foot of the common mussel, Mytilus edulis, and deposited into the bys sal attachment pads. Purification and primary structure of mefp-5 was deter mined by peptide mapping and cDNA sequencing. The protein is 74 residues lo ng and has a mass of about 9500 Da. Mefp-5 composition shows a strong amino acid bias: aromatic amino acids, lysine, and glycine represent 65 mol % of the composition. More than a third of all the residues in the protein are posttranslationally modified by hydroxylation or phosphorylation. The conve rsion of tyrosine to 3, 4-dihydroxyphenyl-L-alanine (DOPA) and serine to O- phosphoserine accounts for the hydroxylation and phosphorylation, respectiv ely. Neither modification is complete since variations in the extent of pho sphorylation and hydroxylation can be detected by mass spectrometry. More t han 75% of the DOPA is adjacent to basic residues, e.g., Lys-DOPA and DOPA- Lys. Phosphoserine occurs in sequences strikingly reminiscent of acidic min eral-binding motifs that appear in statherin, osteopontin, and others. This may be an adaptation for adhesion to the most common substrata for mussels , i.e., calcareous materials.