Myosin X is a high duty ratio motor
Biochemistry & Molecular Pharmacology
Graduate School of Biomedical Sciences; Department of Physiology
Medical Subject Headings
Actins; Adenosine Diphosphate; Adenosine Triphosphatases; Adenosine Triphosphate; Animals; Cattle; Dose-Response Relationship, Drug; Hydrolysis; Kinetics; Models, Chemical; Myosins; Phosphates; Protein Binding; Time Factors
Life Sciences | Medicine and Health Sciences
Myosin X is expressed in a variety of cell types and plays a role in cargo movement and filopodia extension, but its mechanoenzymatic characteristics are not fully understood. Here we analyzed the kinetic mechanism of the ATP hydrolysis cycle of acto-myosin X using a single-headed construct (M10IQ1). Myosin X was unique for the weak "strong actin binding state" (AMD) with a K(d) of 1.6 microm attributed to the large dissociation rate constant (2.1 s(-1)). V(max) and K(ATPase) of the actin-activated ATPase activity of M10IQ1 were 13.5 s(-1) and 17.4 mum, respectively. The ATP hydrolysis rate (>100 s(-1)) and the phosphate release rate from acto-myosin X (>100 s(-1)) were much faster than the entire ATPase cycle rate and, thus, not rate-limiting. The ADP off-rate from acto-myosin X was 23 s(-1), which was two times larger than the V(max). The P(i)-burst size was low (0.46 mol/mol), indicating that the equilibrium is significantly shifted toward the prehydrolysis intermediate. The steady-state ATPase rate can be explained by a combination of the unfavorable equilibrium constant of the hydrolysis step and the relatively slow ADP off-rate. The duty ratio calculated from our kinetic model, 0.6, was consistent with the duty ratio, 0.7, obtained from comparison of K(m ATPase) and K(m motility). Our results suggest that myosin X is a high duty ratio motor.
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Citation: J Biol Chem. 2005 Aug 12;280(32):29381-91. Epub 2005 Jun 16. Link to article on publisher's site
The Journal of biological chemistry
Homma, Kazuaki and Ikebe, Mitsuo, "Myosin X is a high duty ratio motor" (2005). GSBS Student Publications. 535.