title: Calcium-induced mechanical change in the neck domain alters the activity of plant myosin XI.
abstract: Plant myosin XI functions as a motor that generates cytoplasmic streaming in plant cells. Although cytoplasmic streaming is known to be regulated by intracellular Ca(2+) concentration, the molecular mechanism underlying this control is not fully understood. Here, we investigated the mechanism of regulation of myosin XI by Ca(2+) at the molecular level. Actin filaments were easily detached from myosin XI in an in vitro motility assay at high Ca(2+) concentration (pCa 4) concomitant with the detachment of calmodulin light chains from the neck domains. Electron microscopic observations showed that myosin XI at pCa 4 shortened the neck domain by 30%. Single-molecule analysis revealed that the step size of myosin XI at pCa 4 was shortened to 27 nm under low load and to 22 nm under high load compared with 35 nm independent of the load for intact myosin XI. These results indicate that modulation of the mechanical properties of the neck domain is a key factor for achieving the Ca(2+)-induced regulation of cytoplasmic streaming.
authors: Advanced ICT Research Institute, National Institute of Information and Communications Technology, Kobe 651-2492, Japan.
authors: Motoki
authors: M
authors: Tominaga
authors: Hiroaki
authors: H
authors: Kojima
authors: Etsuo
authors: E
authors: Yokota
authors: Rinna
authors: R
authors: Nakamori
authors: Michael
authors: M
authors: Anson
authors: Teruo
authors: T
authors: Shimmen
authors: Kazuhiro
authors: K
authors: Oiwa
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism*; D003595:Cytoplasmic Streaming / Q000502:physiology*; D009218:Myosins / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D014026:Nicotiana / Q000166:cytology / Q000201:enzymology* / Q000235:genetics
chemical_list: D010940:Plant Proteins; D009218:Myosins