title: Molecular characterization and subcellular localization of Arabidopsis class VIII myosin, ATM1.
abstract: Land plants possess myosin classes VIII and XI. Although some information is available on the molecular properties of class XI myosins, class VIII myosins are not characterized. Here, we report the first analysis of the enzymatic properties of class VIII myosin. The motor domain of Arabidopsis class VIII myosin, ATM1 (ATM1-MD), and the motor domain plus one IQ motif (ATM1-1IQ) were expressed in a baculovirus system and characterized. ATM1-MD and ATM1-1IQ had low actin-activated Mg(2+)-ATPase activity (Vmax = 4 s(-1)), although their affinities for actin were high (Kactin = 4 μM). The actin-sliding velocities of ATM1-MD and ATM1-1IQ were 0.02 and 0.089 μm/s, respectively, from which the value for full-length ATM1 is calculated to be ∼0.2 μm/s. The results of actin co-sedimentation assay showed that the duty ratio of ATM1 was ∼90%. ADP dissociation from the actin·ATM1 complex (acto-ATM1) was extremely slow, which accounts for the low actin-sliding velocity, low actin-activated ATPase activity, and high duty ratio. The rate of ADP dissociation from acto-ATM1 was markedly biphasic with fast and slow phase rates (5.1 and 0.41 s(-1), respectively). Physiological concentrations of free Mg(2+) modulated actin-sliding velocity and actin-activated ATPase activity by changing the rate of ADP dissociation from acto-ATM1. GFP-fused full-length ATM1 expressed in Arabidopsis was localized to plasmodesmata, plastids, newly formed cell walls, and actin filaments at the cell cortex. Our results suggest that ATM1 functions as a tension sensor/generator at the cell cortex and other structures in Arabidopsis.
authors.affiliation: From the Department of Biology, Graduate School of Science, Chiba University, Inage-ku, Chiba 263-8522.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Haraguchi
authors.forename: Motoki
authors.initials: M
authors.lastname: Tominaga
authors.forename: Rie
authors.initials: R
authors.lastname: Matsumoto
authors.forename: Kei
authors.initials: K
authors.lastname: Sato
authors.forename: Akihiko
authors.initials: A
authors.lastname: Nakano
authors.forename: Keiichi
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Kohji
authors.initials: K
authors.lastname: Ito
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D004136:Dinitrobenzenes / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D018613:Microscopy, Confocal; D009218:Myosins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011485:Protein Binding; D011523:Protoplasts / Q000166:cytology / Q000378:metabolism; D013424:Sulfanilamides / Q000494:pharmacology; D050257:Tubulin Modulators / Q000494:pharmacology
chemical_list: C000590171:ATM1 class VIII myosin, Arabidopsis; D000199:Actins; D029681:Arabidopsis Proteins; D004136:Dinitrobenzenes; D013424:Sulfanilamides; D050257:Tubulin Modulators; D049452:Green Fluorescent Proteins; D000244:Adenosine Diphosphate; C012465:oryzalin; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins
keywords: ATPases; Actin; Arabidopsis; Kinetics; Molecular Motors; Myosin