title: Structure and mechanism of mouse cyclase-associated protein (CAP1) in regulating actin dynamics.
abstract: Srv2/CAP is a conserved actin-binding protein with important roles in driving cellular actin dynamics in diverse animal, fungal, and plant species. However, there have been conflicting reports about whether the activities of Srv2/CAP are conserved, particularly between yeast and mammalian homologs. Yeast Srv2 has two distinct functions in actin turnover: its hexameric N-terminal-half enhances cofilin-mediated severing of filaments, while its C-terminal-half catalyzes dissociation of cofilin from ADP-actin monomers and stimulates nucleotide exchange. Here, we dissected the structure and function of mouse CAP1 to better understand its mechanistic relationship to yeast Srv2. Although CAP1 has a shorter N-terminal oligomerization sequence compared with Srv2, we find that the N-terminal-half of CAP1 (N-CAP1) forms hexameric structures with six protrusions, similar to N-Srv2. Further, N-CAP1 autonomously binds to F-actin and decorates the sides and ends of filaments, altering F-actin structure and enhancing cofilin-mediated severing. These activities depend on conserved surface residues on the helical-folded domain. Moreover, N-CAP1 enhances yeast cofilin-mediated severing, and conversely, yeast N-Srv2 enhances human cofilin-mediated severing, highlighting the mechanistic conservation between yeast and mammals. Further, we demonstrate that the C-terminal actin-binding β-sheet domain of CAP1 is sufficient to catalyze nucleotide-exchange of ADP-actin monomers, while in the presence of cofilin this activity additionally requires the WH2 domain. Thus, the structures, activities, and mechanisms of mouse and yeast Srv2/CAP homologs are remarkably well conserved, suggesting that the same activities and mechanisms underlie many of the diverse actin-based functions ascribed to Srv2/CAP homologs in different organisms.
authors.affiliation: Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, Massachusetts 02454 and.
authors.forename: Silvia
authors.initials: S
authors.lastname: Jansen
authors.affiliation: Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, Massachusetts 02454 and.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Collins
authors.affiliation: Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, Massachusetts 02454 and.
authors.forename: Leslie
authors.initials: L
authors.lastname: Golden
authors.affiliation: Faculty of Biology, Moscow State University, GSP-1, 1 Leninskie Gory, Building 12, 119991 Moscow, Russia.
authors.forename: Olga
authors.initials: O
authors.lastname: Sokolova
authors.affiliation: Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, Massachusetts 02454 and. Electronic address: goode@brandeis.edu.
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Goode
mesh_terms: D051339:Actin Depolymerizing Factors / Q000737:chemistry; D000199:Actins / Q000737:chemistry* / Q000648:ultrastructure; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry; D000244:Adenosine Diphosphate / Q000737:chemistry; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000737:chemistry; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry; D013045:Species Specificity
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; C073751:SRV2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C525401:CAP1 cyclase-associated protein, mouse; D000244:Adenosine Diphosphate
keywords: Actin; Cofilin; Cyclase-associated Protein; Electron Microscopy (EM); Fluorescence; Microscopic Imaging; Severing; Srv2