HYDROXYARGININE-CONTAINING POLYPHENOLIC PROTEINS IN THE ADHESIVE PLAQUES OF THE MARINE MUSSEL MYTILUS-EDULIS

An unusual polymorphic protein family of nine or more variants has bee n isolated from the byssal adhesive plaques and foot of the marine mus sel Mytilus edulis. In accordance with established terminology, the fa mily is referred to as IM. edulis foot protein 3 or simply Mefp-3. Var iants of Mefp-S have molecular masses of about 6 kDa, isoelectric poin ts greater than 10.5, and an amino acid composition dominated by six a mino acids: glycine, asparagine, 3,4-dihydroxyphenylalanine (Dopa), tr yptophan, arginine, and an unknown basic amino acid. The latter has be en isolated and identified as 4-hydroxyarginine using fast atom bombar dment mass spectrometry and appropriate standards. The primary structu re of variant Mefp-3F has been determined by peptide mapping using aut omated Edman sequencing in combination with fast atom bombardment and matrix-assisted laser desorption ionization mass spectrometry: ADYYGPN YGPPRRYGGGNYNRYNRYGRRYGGYKGWNNGWNRGRRGKYW where Y represents Dopa, and R represents hydroxyarginine. Notably, the 4 occurrences of RY are ma rked by a resistance to trypsin digestion. Although the conversion of tyrosines to Dopa is essentially complete, hydroxylation of arginines varies between 40 and 80%. In contrast to other mussel adhesive protei ns such as Mefp-1 and -2 which have large numbers of highly conserved, tandemly repeated peptide motifs, Mefp-3 has only short sporadic repe ats. The specific function of Mefp-3 in byssal adhesion is unknown.