SUPERVILLIN (P205) - A NOVEL MEMBRANE-ASSOCIATED, F-ACTIN-BINDING PROTEIN IN THE VILLIN GELSOLIN SUPERFAMILY/

Actin-binding membrane proteins are involved in both adhesive interact ions and motile processes. We report here the purification and initial characterization of p205, a 205-kD protein from bovine neutrophil pla sma membranes that binds to the sides of actin filaments in blot overl ays. p205 is a tightly bound peripheral membrane protein that cosedime nts with endogenous actin in sucrose gradients and immunoprecipitates. Amino acid sequences were obtained from SDS-PAGE-purified p205 and us ed to generate antipeptide antibodies, immunolocalization data, and cD NA sequence information. The intracellular localization of p205 in MDB K cells is a function of cell density and adherence state. In subconfl uent cells, p205 is found in punctate spots along the plasma membrane and in the cytoplasm and nucleus; in adherent cells, p205 concentrates with E-cadherin at sites of lateral cell-cell contact. Upon EGTA-medi ated cell dissociation, p205 is internalized with E-cadherin and F-act in as a component of adherens junctions ''rings.'' At later times, p20 5 is observed in cytoplasmic punctae. The high abundance of p205 in ne utrophils and suspension-grown HeLa cells, which lack adherens junctio ns, further suggests that this protein may play multiple roles during cell growth, adhesion, and motility. Molecular cloning of p205 cDNA re veals a bipartite structure. The COOH terminus exhibits a striking sim ilarity to villin and gelsolin, particularly in regions known to bind F-actin. The NH2 terminus is novel, but contains four potential nuclea r targeting signals. Because p205 is now the largest known member of t he villin/gelsolin superfamily, we propose the name, ''supervillin.'' We suggest that supervillin may be involved in actin filament assembly at adherens junctions and that it may play additional roles in other cellular compartments.