title: UNC-87 is an actin-bundling protein.
abstract: The Caenorhabditis elegans unc-87 gene product is essential for the maintenance of the nematode body wall muscle where it is found colocalized with actin in the I band. The molecular domain structure of the protein reveals similarity to the C-terminal repeat region of the smooth muscle actin-binding protein calponin. In this study we investigated the in vitro function of UNC-87 using both the full-length recombinant molecule and several truncated mutants. According to analytical ultracentrifugation UNC-87 occurs as a monomer in solution. UNC-87 cosedimented with both smooth and skeletal muscle F-actin, but not with monomeric G-actin, and exhibited potent actin filament bundling activity. Actin binding was independent of the presence of tropomyosin and the actin cross-linking proteins filamin and alpha-actinin. Consistent with its actin bundling activity in vitro, UNC-87 tagged with green fluorescent protein associated with and promoted the formation of actin stress fiber bundles in living cells. These data identify UNC-87 as an actin-bundling protein and highlight the calponin-like repeats as a novel actin-binding module.
authors.affiliation: Department of Cell Biology, Institute of Molecular Biology, Austrian Academy of Sciences, Billrothstrasse 11, A-5020 Salzburg, Austria.
authors.forename: W J
authors.initials: WJ
authors.lastname: Kranewitter
authors.forename: J
authors.initials: J
authors.lastname: Ylanne
authors.forename: M
authors.initials: M
authors.lastname: Gimona
mesh_terms: D000199:Actins / Q000737:chemistry*; D000818:Animals; D001483:Base Sequence; D029742:Caenorhabditis elegans Proteins; D002478:Cells, Cultured; D015801:Helminth Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000502:physiology; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000502:physiology; D011817:Rabbits; D011994:Recombinant Proteins / Q000302:isolation & purification; D020449:Repetitive Sequences, Amino Acid
chemical_list: D000199:Actins; D029742:Caenorhabditis elegans Proteins; D015801:Helminth Proteins; D009124:Muscle Proteins; D011994:Recombinant Proteins; C089652:UNC-87 protein, C elegans