title: Structures linking microfilament bundles to the membrane at focal contacts.
abstract: We used quick-freeze, deep-etch, rotary replication and immunogold cytochemistry to identify a new structure at focal contacts. In Xenopus fibroblasts, elongated aggregates of particles project from the membrane to contact bundles of actin microfilaments. Before terminating, a single bundle of microfilaments interacts with several aggregates that appear intermittently over a distance of several microns. Aggregates are enriched in proteins believed to mediate actin-membrane interactions at focal contacts, including beta 1-integrin, vinculin, and talin, but they appear to contain less alpha-actinin and filamin. We also identified a second, smaller class of aggregates of membrane particles that contained beta 1-integrin but not vinculin or talin and that were not associated with actin microfilaments. Our results indicate that vinculin, talin, and beta 1-integrin are assembled into distinctive structures that mediate multiple lateral interactions between microfilaments and the membrane at focal contacts.
authors.affiliation: Department of Physiology, University of Maryland School of Medicine, Baltimore 21201.
authors.forename: S J
authors.initials: SJ
authors.lastname: Samuelsson
authors.forename: P W
authors.initials: PW
authors.lastname: Luther
authors.forename: D W
authors.initials: DW
authors.lastname: Pumplin
authors.forename: R J
authors.initials: RJ
authors.lastname: Bloch
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry / Q000648:ultrastructure*; D000185:Actinin / Q000032:analysis; D000199:Actins / Q000032:analysis; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry / Q000648:ultrastructure*; D002478:Cells, Cultured; D003285:Contractile Proteins / Q000032:analysis; D005109:Extracellular Matrix / Q000648:ultrastructure; D005347:Fibroblasts; D064448:Filamins; D005613:Freeze Etching; D007150:Immunohistochemistry; D019012:Integrin beta1; D016023:Integrins / Q000032:analysis; D008840:Microfilament Proteins / Q000032:analysis; D008854:Microscopy, Electron; D016608:Talin / Q000032:analysis; D016596:Vinculin / Q000032:analysis; D014982:Xenopus laevis
chemical_list: D000199:Actins; D003285:Contractile Proteins; D064448:Filamins; D019012:Integrin beta1; D016023:Integrins; D008840:Microfilament Proteins; D016608:Talin; D000185:Actinin; D016596:Vinculin