The byssus of the zebra mussel, Dreissena polymorpha. II: Structure and polymorphism of byssal polyphenolic protein families.

The byssus of the zebra mussel Dreissena polymorpha is the key element of its adhesive strategy. It consists of a bundle of threads tipped by adhesive plaques and attached to the mussel at the base of its byssal-synthesizing organ, the foot. Two polyphenolic protein precursors of the byssus have been purified from the foot. These precursors, Dpfp-1 and Dpfp-2 (Dreissena polymorpha foot protein), with apparent M(r) values of 76 and 26 K, respectively, contain 3,4-dihydroxyphenylalanine (DOPA) integrated into their primary sequence, but differ from previously characterized polyphenolic proteins from marine mussels. The related quagga mussel (Dreissena spp.?) has homologous proteins with significantly different compositions. The zebra mussel DOPA proteins are tandemly repetitive with unique oligopeptide motif sequences, contain tryptophan, and are O-glycosylated primarily on threonine residues. Galactosamine was the only carbohydrate detected after hydrolysis. Dpfp-1 constitutes a polymorphic family of polypeptides with, unusually, an acidic range of pI values between 5.3 and 6.5. The detection of carbohydrate in the thread and in the juncture between thread and plaque suggests that these two proteins are localized in those regions where they may function as lacquers or structural elements.