Higher plant myosin XI moves processively on actin with 35 nm steps at high velocity.
High velocity cytoplasmic streaming is found in various plant cells from algae to angiosperms. We characterized mechanical and enzymatic properties of a higher plant myosin purified from tobacco bright yellow-2 cells, responsible for cytoplasmic streaming, having a 175 kDa heavy chain and calmodulin light chains. Sequence analysis shows it to be a class XI myosin and a dimer with six IQ motifs in the light chain-binding domains of each heavy chain. Electron microscopy confirmed these predictions. We measured its ATPase characteristics, in vitro motility and, using optical trap nanometry, forces and movement developed by individual myosin XI molecules. Single myosin XI molecules move processively along actin with 35 nm steps at 7 micro m/s, the fastest known processive motion. Processivity was confirmed by actin landing rate assays. Mean maximal force was approximately 0.5 pN, smaller than for myosin IIs. Dwell time analysis of beads carrying single myosin XI molecules fitted the ATPase kinetics, with ADP release being rate limiting. These results indicate that myosin XI is highly specialized for generation of fast processive movement with concomitantly low forces.
Tominaga
Motoki
M
Kansai Advanced Research Center, Communications Research Laboratory, Kobe 651-2492, Japan.
Kojima
Hiroaki
H
Yokota
Etsuo
E
Orii
Hidefumi
H
Nakamori
Rinna
R
Katayama
Eisaku
E
Anson
Michael
M
Shimmen
Teruo
T
Oiwa
Kazuhiro
K
D000199:Actins / Q000737:chemistry* / Q000648:ultrastructure; D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000032:analysis; D000255:Adenosine Triphosphate / Q000494:pharmacology; D002148:Calmodulin-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D003595:Cytoplasmic Streaming; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D020409:Molecular Motor Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D008969:Molecular Sequence Data; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000648:ultrastructure; D018994:Myosin Light Chains / Q000737:chemistry / Q000648:ultrastructure; D009218:Myosins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D036103:Nanotechnology; D014026:Nicotiana / Q000737:chemistry
D000199:Actins; D002148:Calmodulin-Binding Proteins; D020409:Molecular Motor Proteins; D018994:Myosin Light Chains; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D018995:Myosin Heavy Chains; D009218:Myosins