title: The N-terminal domain of MYO18A has an ATP-insensitive actin-binding site.
abstract: Myosin XVIII is the recently identified 18th class of myosins, and its members are composed of a unique N-terminal domain, a motor domain with an unusual sequence around the ATPase site, one IQ motif, a segmented coiled-coil region for dimerization, and a C-terminal globular tail. To gain insight into the functions of this unique myosin, we characterized its human homologue, MYO18A, focusing on the functional roles of the characteristic N-terminal domain that contains a PDZ module known to mediate protein-protein interaction. GFP-tagged full-length and C-terminally truncated MYO18A molecules that were expressed in HeLa cells exhibited colocalization with actin filaments. Chemical cross-linking of these molecules showed that they form stable dimers as expected from their putative coiled-coil tails. Cosedimentation of the various types of truncated MYO18A constructs with actin filaments indicated the presence of an ATP-insensitive actin-binding site in the N-terminal domain. Further studies on truncated constructs of the N-terminal domain indicated that this actin-binding site is located outside the PDZ module, but within the middle region of this domain, which does not show any homology with the known actin-binding motifs. These results imply that this dimeric myosin might stably cross-link actin filaments by two ATP-insensitive actin-binding sites at the N-terminal domains for higher-order organization of the actin cytoskeleton.
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Tokyo 153-8902, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Isogawa
authors.forename: Takahide
authors.initials: T
authors.lastname: Kon
authors.forename: Takeshi
authors.initials: T
authors.lastname: Inoue
authors.forename: Reiko
authors.initials: R
authors.lastname: Ohkura
authors.forename: Hisashi
authors.initials: H
authors.lastname: Yamakawa
authors.forename: Osamu
authors.initials: O
authors.lastname: Ohara
authors.forename: Kazuo
authors.initials: K
authors.lastname: Sutoh
mesh_terms: D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D004247:DNA / Q000235:genetics; D019281:Dimerization; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009218:Myosins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D000199:Actins; D011993:Recombinant Fusion Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D009218:Myosins