Cloning, expression, and immunolocalization of a byssal precursor protein from the zebra mussel, Dreissena polymorpha (Pallas)

The zebra mussel, Dreissena polymorpha (Pallas), is a nonindigenous invader of North American lakes and rivers and one of only a few freshwater bivalve molluscs having a byssus—an extracellular structure composed of a network of highly cross-linked proteins used to attach the mussel to hard surfaces. In this study, partial and full-length cDNA sequences were obtained for an important byssal precursor protein, Dreissena polymorpha foot protein 1 (Dpfp1). The deduced primary sequence of Dpfp1 was composed of a block copolymer-like structure defined by two consensus motifs that are sharply segregated into domains. The N-terminal half of Dpfp1 was dominated by a previously unreported tandemly repeating heptapeptide (P-[V/E]-Y-P-[T/S/D]-[K/Q]-X) while the C-terminal half of the protein was composed almost exclusively of a previously reported (Rzepecki and Waite, 1993b) tridecapeptide (K-P-G-P-Y-D-Y-D-G-P-Y-D-K). A bacterial expression system was successfully used to produce a recombinant protein encoding the complete primary sequence of mature Dpfp1. Recombinant Dpfp1 was used as an antigen to produce polyclonal antibodies directed against the native protein. Western blots of zebra mussel foot tissue and byssal thread extracts exposed to the antibody demonstrated that the antibodies were capable of specifically detecting the native protein in both tissues. The absence of an antibody-positive band in all other tissues demonstrated that Dpfp1 is manufactured exclusively by glands in the foot. Confocal micrographs of immunofluorescently labeled foot tissue sections detected antibody-positive cytoplasmic granules in tissue surrounding the ventral groove as well as in the groove itself. The distribution of antibody-positive granules in foot tissue and within the groove suggest that Dpfp1 is an important structural protein uniformly distributed throughout byssal threads and plaques.