Glycosylated Hydroxytryptophan in a Mussel Adhesive Protein from Perna viridis

The 3,4-dihydroxyphenyl-L-alanine (Dopa)-containing proteins of mussel byssus play a critical role in wet adhesion and have inspired versatile new synthetic strategies for adhesives and coatings. Apparently, however, not all mussel adhesive proteins are beholden to Dopa chemistry. The cDNA-deduced sequence of Pvfp-1, a highly aromatic and redox active byssal coating protein in the green mussel Perna viridis, suggests that Dopa may be replaced by a post-translational modification of tryptophan. The N-terminal tryptophan-rich domain of Pvfp-1 contains 42 decapeptide repeats with the consensus sequences ATPKPW(1)TAW(2)K and APPPAW(1)TAW(2)K. A small collagen domain (18 Gly-X-Y repeats) is also present. Tandem mass spectrometry of isolated tryptic decapeptides has detected both C-2-hexosylated tryptophan(W-1) and C-2-hexosylated hydroxytryptophan (W-2), the latter of which is redox active. The UV absorbance spectrum of W-2 is consistent with 7-hydroxytryptophan, which represents an intriguing new theme for bioinspired opportunistic wet adhesion.