title: Srv2/cyclase-associated protein forms hexameric shurikens that directly catalyze actin filament severing by cofilin.
abstract: Actin filament severing is critical for the dynamic turnover of cellular actin networks. Cofilin severs filaments, but additional factors may be required to increase severing efficiency in vivo. Srv2/cyclase-associated protein (CAP) is a widely expressed protein with a role in binding and recycling actin monomers ascribed to domains in its C-terminus (C-Srv2). In this paper, we report a new biochemical and cellular function for Srv2/CAP in directly catalyzing cofilin-mediated severing of filaments. This function is mediated by its N-terminal half (N-Srv2), and is physically and genetically separable from C-Srv2 activities. Using dual-color total internal reflection fluorescence microscopy, we determined that N-Srv2 stimulates filament disassembly by increasing the frequency of cofilin-mediated severing without affecting cofilin binding to filaments. Structural analysis shows that N-Srv2 forms novel hexameric star-shaped structures, and disrupting oligomerization impairs N-Srv2 activities and in vivo function. Further, genetic analysis shows that the combined activities of N-Srv2 and Aip1 are essential in vivo. These observations define a novel mechanism by which the combined activities of cofilin and Srv2/CAP lead to enhanced filament severing and support an emerging view that actin disassembly is controlled not by cofilin alone, but by a more complex set of factors working in concert.
authors.affiliation: Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454, USA.
authors.forename: Faisal
authors.initials: F
authors.lastname: Chaudhry
authors.forename: Dennis
authors.initials: D
authors.lastname: Breitsprecher
authors.forename: Kristin
authors.initials: K
authors.lastname: Little
authors.forename: Grigory
authors.initials: G
authors.lastname: Sharov
authors.forename: Olga
authors.initials: O
authors.lastname: Sokolova
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Goode
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002232:Carbocyanines / Q000737:chemistry; D002384:Catalysis; D051338:Cofilin 1 / Q000737:chemistry / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence / Q000379:methods; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D055503:Protein Multimerization; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C495813:COF1 protein, S cerevisiae; D002232:Carbocyanines; D051338:Cofilin 1; D003598:Cytoskeletal Proteins; D008840:Microfilament Proteins; C073751:SRV2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C115237:actin interacting protein 1; C089187:cyanine dye 3