Effects of urea and guanidine hydrochloride on the sliding movement of actin filaments with ATP hydrolysis by myosin molecules

Ryusei Kumemoto, Yoshitsugu Hosogoe, Naoki Nomura, and Kuniyuki Hatori*

Department of Bio-System Engineering,

Graduate School of Science and Technology,

Yamagata University

Yonezawa 992-8510, Japan

Summary

　 To evaluate the role of the hydration layer on the protein surface of actomyosin, we compared the effects of urea and guanidine-HCl on the sliding velocities and ATPase activities of the actin-heavy meromyosin (HMM) system. Both chemicals denature proteins, but only urea perturbs the hydration layer. Both the sliding velocity of actin filaments and actin-activated ATPase activity decreased with increasing urea concentrations. The sliding movement was completely inhibited at 1.0 M urea, while actin filaments were bound to HMM molecules fixed on the glass surface. Guanidine-HCl (0–0.05 M) drastically decreased both the sliding velocity and ATPase activation of acto-HMM complexes. Under this condition, actin filaments almost detached from HMM molecules. In contrast, the ATPase activity of HMM without actin filaments was almost independent of urea concentrations below 1.0 M and guanidine-HCl concentrations below 0.05 M. An increase in urea concentrations up to 2.0 M partly induced changes in the ternary structure of HMM molecules, while the actin filaments were stable in this concentration range. Hydration changes around such actomyosin complexes may alter both the stability of part of the myosin molecules, and the affinity for force transmission between actin filaments and myosin heads.

Keywords: actomyosin; ATP hydrolysis; denaturant; hydration; motility