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Coordinated regulation of actin filament turnover by a high-molecular-weight Srv2/CAP complex, cofilin, profilin, and Aip1.

BACKGROUND: Dynamic remodeling of the actin cytoskeleton requires rapid turnover of actin filaments, which is regulated in part by the actin filament severing/depolymerization factor cofilin/ADF. Two factors that cooperate with cofilin are Srv2/CAP and Aip1. Human CAP enhances cofilin-mediated actin turnover in vitro, but its biophysical properties have not been defined, and there has been no in vivo evidence reported for its role in turnover. Xenopus Aip1 forms a cofilin-dependent cap at filament barbed ends. It has been unclear how these diverse activities are coordinated in vivo. RESULTS: Purified native yeast Srv2/CAP forms a high molecular weight structure comprised solely of actin and Srv2. The complex is linked to actin filaments via the SH3 domain of Abp1. Srv2 complex catalytically accelerates cofilin-dependent actin turnover by releasing cofilin from ADP-actin monomers and enhances the ability of profilin to stimulate nucleotide exchange on ADP-actin. Yeast Aip1 forms a cofilin-dependent filament barbed end cap, disrupted by the cof1-19 mutant. Genetic analyses show that specific combinations of activities mediated by cofilin, Srv2, Aip1, and capping protein are required in vivo. CONCLUSIONS: We define two genetically and biochemically separable functions for cofilin in actin turnover. One is formation of an Aip1-cofilin cap at filament barbed ends. The other is cofilin-mediated severing/depolymerization of filaments, accelerated indirectly by Srv2 complex. We show that the Srv2 complex is a large multimeric structure and functions as an intermediate in actin monomer processing, converting cofilin bound ADP-actin monomers to profilin bound ATP-actin monomers and recycling cofilin for new rounds of filament depolymerization.

Pubmed ID: 14680631


  • Balcer HI
  • Goodman AL
  • Rodal AA
  • Smith E
  • Kugler J
  • Heuser JE
  • Goode BL


Current biology : CB

Publication Data

December 16, 2003

Associated Grants

  • Agency: NIGMS NIH HHS, Id: GM 29647
  • Agency: NIGMS NIH HHS, Id: GM 63691
  • Agency: NIGMS NIH HHS, Id: R01 GM063691

Mesh Terms

  • Actin Cytoskeleton
  • Actin Depolymerizing Factors
  • Adaptor Proteins, Signal Transducing
  • Cell Cycle Proteins
  • Chromatography, Gel
  • Contractile Proteins
  • Cytoskeletal Proteins
  • Electrophoresis, Polyacrylamide Gel
  • Gene Transfer Techniques
  • Immunoblotting
  • Microfilament Proteins
  • Microscopy, Electron
  • Models, Molecular
  • Profilins
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Serine Endopeptidases
  • Xenopus Proteins
  • src Homology Domains