Motor Function and Regulation of Myosin X

Kazuaki Homma, Junya Saito, Reiko Ikebe, Mitsuo Ikebe*

*Corresponding author for this work

Research output: Contribution to journalArticle

49 Scopus citations

Abstract

Myosin X is a member of the diverse myosin superfamily that is ubiquitously expressed in various mammalian tissues. Although its association with actin in cells has been shown, little is known about its biochemical and mechanoenzymatic function at the molecular level. We expressed bovine myosin X containing the entire head, neck, and coiled-coil domain and purified bovine myosin X in Sf9 cells. The Mg2+-ATPase activity of myosin X was significantly activated by actin with low KATP. The actin-activated ATPase activity was reduced at Ca2+ concentrations above pCa 5 in which 1 mol of calmodulin light chain dissociates from the heavy chain. Myosin X translocates F-actin filaments with the velocity of 0.3 μm/s with the direction toward the barbed end. The actin translocating activity was inhibited at concentrations of Ca2+ at pCa 6 in which no calmodulin dissociation takes place, suggesting that the calmodulin dissociation is not required for the inhibition of the motility. Unlike class V myosin, which shows a high affinity for F-actin in the presence of ATP, the Kactin of the myosin X ATPase was much higher than that of myosin V. Consistently nearly all actin dissociated from myosin X in the presence of ATP. ADP did not significantly inhibit the actin-activated ATPase activity of myosin X, suggesting that the ADP release step is not rate-limiting. These results suggest that myosin X is a nonprocessive motor. Consistently myosin X failed to support the actin translocation at low density in an in vitro motility assay where myosin V, a processive motor, supports the actin filament movement.

Original languageEnglish (US)
Pages (from-to)34348-34354
Number of pages7
JournalJournal of Biological Chemistry
Volume276
Issue number36
DOIs
StatePublished - Sep 7 2001

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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