title: The V-ATPase subunit C binds to polymeric F-actin as well as to monomeric G-actin and induces cross-linking of actin filaments.
abstract: Previously, we have shown that the V-ATPase holoenzyme as well as the V1 complex isolated from the midgut of the tobacco hornworm (Manduca sexta) exhibits the ability of binding to actin filaments via the V1 subunits B and C (Vitavska, O., Wieczorek, H., and Merzendorfer,H. (2003) J. Biol. Chem. 278, 18499-18505). Since the recombinant subunit C not only enhances actin binding of the V1 complex but also can bind separately to F-actin, we analyzed the interaction of recombinant subunit C with actin. We demonstrate that it binds not only to F-actin but also to monomeric G-actin. With dissociation constants of approximately 50 nm, the interaction exhibits a high affinity, and no difference could be observed between binding to ATP-G-actin or ADP-G-actin, respectively. Unlike other proteins such as members of the ADF/cofilin family, which also bind to G- as well as to F-actin, subunit C does not destabilize actin filaments. On the contrary, under conditions where the disassembly of F-actin into G-actin usually occurred, subunit C stabilized F-actin. In addition, it increased the initial rate of actin polymerization in a concentration-dependent manner and was shown to cross-link actin filaments to bundles of varying thickness. Apparently bundling is enabled by the existence of at least two actin-binding sites present in the N- and in the C-terminal halves of subunits C, respectively. Since subunit C has the possibility to dimerize or even to oligomerize, spacing between actin filaments could be variable in size.
authors.affiliation: Department of Biology/Chemistry, Division of Animal Physiology, University of Osnabrück, 49069 Osnabrück, Germany.
authors.forename: Olga
authors.initials: O
authors.lastname: Vitavska
authors.forename: Hans
authors.initials: H
authors.lastname: Merzendorfer
authors.forename: Helmut
authors.initials: H
authors.lastname: Wieczorek
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000378:metabolism*; D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism*; D019281:Dimerization; D018402:Manduca; D011485:Protein Binding; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000199:Actins; D001704:Biopolymers; D021122:Protein Subunits; D025262:Vacuolar Proton-Translocating ATPases