title: Homotypic dimerization of the actin-binding protein p57/coronin-1 mediated by a leucine zipper motif in the C-terminal region.
abstract: The actin-binding protein p57/coronin-1, a member of the coronin protein family, is selectively expressed in immune cells, and has been implicated in leucocyte migration and phagocytosis by virtue of its interaction with F-actin (filamentous actin). We previously identified two sites in the N-terminal region of p57/coronin-1 by which it binds actin, and in the present study we examine the role of the leucine zipper motif located in the C-terminal coiled-coil domain in mediating the homotypic association of p57/coronin-1. Recombinant p57/coronin-1 protein in solution formed a homodimer, as analysed by Superose 12 column chromatography and by sucrose density gradient centrifugation. In vivo, a truncated form consisting of the C-terminal coiled-coil domain co-precipitated with full-length p57/coronin-1 when both were co-expressed in COS-1 cells. A chimaeric construct composed of the C-terminal domain of p57/coronin-1 (which lacks the actin-binding sites) fused with green fluorescent protein co-localized with cortical F-actin-rich regions in COS-1 cells only when full-length p57/coronin-1 was expressed simultaneously in the cells, suggesting that the C-terminal region is required for the homotypic association of p57/coronin-1. Furthermore, p57LZ, a polypeptide consisting of the C-terminal 90 amino acid residues of p57/coronin-1, was sufficient for dimerization. When two leucine residues out of the four that constitute the leucine zipper structure in p57LZ or full-length p57 were replaced with alanine residues, the mutants failed to form homodimers. Taken together, these results demonstrate that p57/coronin-1 forms homodimers, that the association is mediated by the leucine zipper structure in the C-terminal region, and that it plays a role in the cross-linking of F-actin in the cell.
authors.affiliation: Department of Microbiology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, 2-4-41 Ebara, Shinagawa-ku, Tokyo 142-8501, Japan.
authors.forename: Teruaki
authors.initials: T
authors.lastname: Oku
authors.forename: Saotomo
authors.initials: S
authors.lastname: Itoh
authors.forename: Rie
authors.initials: R
authors.lastname: Ishii
authors.forename: Kensuke
authors.initials: K
authors.lastname: Suzuki
authors.forename: William M
authors.initials: WM
authors.lastname: Nauseef
authors.forename: Satoshi
authors.initials: S
authors.lastname: Toyoshima
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Tsuji
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D019281:Dimerization; D004926:Escherichia coli; D006801:Humans; D016350:Leucine Zippers / Q000502:physiology*; D008840:Microfilament Proteins / Q000737:chemistry* / Q000502:physiology; D009154:Mutation; D011993:Recombinant Fusion Proteins
chemical_list: D008840:Microfilament Proteins; D011993:Recombinant Fusion Proteins; C072061:coronin proteins