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Worcester Foundation for Biomedical Research, an Affiliate of the University of Massachusetts Medical Center, Shrewsbury,
Massachusetts 01545
Actin-binding membrane proteins are involved in both adhesive interactions and motile processes. We report here the purification and initial characterization of p205, a 205-kD protein from bovine neutrophil plasma membranes that binds to the sides of
actin filaments in blot overlays. p205 is a tightly bound
peripheral membrane protein that cosediments with
endogenous actin in sucrose gradients and immunoprecipitates. Amino acid sequences were obtained from SDS-PAGE-purified p205 and used to generate antipeptide antibodies, immunolocalization data, and
cDNA sequence information. The intracellular localization of p205 in MDBK cells is a function of cell density and adherence state. In subconfluent 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-mediated cell dissociation, p205 is internalized with E-cadherin and F-actin as
a component of adherens junctions "rings." At later
times, p205 is observed in cytoplasmic punctae. The
high abundance of p205 in neutrophils and suspension-grown HeLa cells, which lack adherens junctions, further suggests that this protein may play multiple roles
during cell growth, adhesion, and motility. Molecular
cloning of p205 cDNA reveals a bipartite structure. The
COOH terminus exhibits a striking similarity to villin
and gelsolin, particularly in regions known to bind
F-actin. The NH2 terminus is novel, but contains four
potential nuclear targeting signals. Because p205 is now
the largest known member of the 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.
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