HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

J. Biol. Chem., Vol. 282, Issue 18, 13228-13239, May 4, 2007

This Article Full Text Full Text (PDF) All Versions of this Article: 282/18/13228    most recent M610766200v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sato, O. Articles by Ikebe, M. Search for Related Content PubMed PubMed Citation Articles by Sato, O. Articles by Ikebe, M. Social Bookmarking                      What's this?

Myosin Va Becomes a Low Duty Ratio Motor in the Inhibited Form^*

From the Department of Physiology, University of Massachusetts Medical School, Worcester, Massachueetts 01655

Vertebrate myosin Va is a typical processive motor with high duty ratio. Recent studies have revealed that the actin-activated ATPase activity of the full-length myosin Va (M5aFull) is inhibited at a low [Ca²⁺], which is due to the formation of a folded conformation of M5aFull. To clarify the underlying inhibitory mechanism, we analyzed the actin-activated ATP hydrolysis mechanism of the M5aFull at the inhibited and the activated states, respectively. Marked differences were found in the hydrolysis, P_i release, and ADP release steps between the activated and the inhibited states. The kinetic constants of these steps of the activated state were similar to those of the unregulated S1 construct, in which the rate-limiting step was the ADP release step. On the other hand, the P_i release rate from acto-M5aFull was decreased in EGTA by >1,000-fold, which makes this step the rate-limiting step for the actin-activated ATP hydrolysis cycle of M5aFull. The ADP off rate from acto-M5aFull was decreased by 10-fold, and the equilibrium between the prehydrolysis state and the post hydrolysis state was shifted toward the former state in the inhibited state of M5aFull. Because of these changes, M5aFull spends a majority of the ATP hydrolysis cycling time in the weak actin binding state. The present results indicate that M5aFull molecules at a low [Ca²⁺] is inhibited as a cargo transporter not only due to the decrease in the cross-bridge cycling rate but also due to the decrease in the duty ratio thus being dissociated from actin.

Received for publication, November 20, 2006 , and in revised form, February 6, 2007.

^* This work was supported by National Institutes of Health Grants AR41653, AR048526, and DC006103 (to M. I.) and an American Heart Association scientist development grant (to X.-D. L.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Physiology, University of Massachusetts Medical School, 55 Lake Ave. N., Worcester, MA 01655. Tel.: 508-856-1954; Fax: 508-856-4600; E-mail: Mitsuo.Ikebe{at}umassmed.edu.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				X.-d. Li, H. S. Jung, Q. Wang, R. Ikebe, R. Craig, and M. Ikebe The globular tail domain puts on the brake to stop the ATPase cycle of myosin Va PNAS, January 29, 2008; 105(4): 1140 - 1145. [Abstract] [Full Text] [PDF]