The neck domain of myosin II primarily regulates the actomyosin kinetics, not the stepsize.
In order to study the role of the neck domain of myosin in muscle contraction, we measured the steps of individual myosin II molecules engineered to have no neck domain (light chain-binding domain) by optical trapping nanometry. The actin filament and myosin cofilaments interacted on a glass surface to minimize the angle between them, and to minimize the interaction between myosin and the glass surface. The results showed that the average myosin stepsize did not change much when the neck domain was removed, but the sliding velocity decreased approximately fivefold. Furthermore, the duration of steps for neckless myosin was several times longer at saturated ATP concentration, indicating that the slower velocity was due to a slower dissociation rate of myosin heads from actin. From these data, we conclude that the neck domain of myosin-II primarily regulates the actomyosin kinetics, not the mechanics.
Hikikoshi Iwane
Atsuko
A
Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan. iwane@phys1.med.osaka-u.ac.jp
Tanaka
Hiroto
H
Morimoto
Sayuri
S
Ishijima
Akihiko
A
Yanagida
Toshio
T
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002645:Chickens; D004023:Dictyostelium / Q000378:metabolism; D008958:Models, Molecular; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology; D024462:Myosin Type II / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D000199:Actins; D011993:Recombinant Fusion Proteins; D024462:Myosin Type II