The heavy chains of the class IX myosins, rat myr5 and human myosin-IXb, contain within their tail domains a region with sequence homology to GTPase activating proteins for the rho family of G proteins. Because low levels of myosin-IXb expression preclude purification by conventional means, we have employed an immunoadsorption strategy to purify myosin-IXb, enabling us to characterize the mechanochemical and rho-GTPase activation properties of the native protein. In this report we have examined the light chain content, actin binding properties, in vitro motility and rho-GTPase activity of human myosin-IXb purified from leukocytes. The results presented here indicate that myosin-IXb contains calmodulin as a light chain and that it binds to actin with high affinity in both the absence and presence of ATP. Myosin-IXb is an active motor which, like other calmodulin-containing myosins, exhibits maximal velocity of actin filaments (15 nm/second) in the absence of Ca2+. Native myosin-IXb exhibits GAP activity on rho. Class IX myosins may be an important link between rho and rho-dependent remodeling of the actin cytoskeleton.
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JOURNAL ARTICLE| 01 April 1998
Human myosin-IXb is a mechanochemically active motor and a GAP for rho
Online Issn: 1477-9137
Print Issn: 0021-9533
© 1998 by Company of Biologists
J Cell Sci (1998) 111 (7): 941–950.
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P.L. Post, G.M. Bokoch, M.S. Mooseker; Human myosin-IXb is a mechanochemically active motor and a GAP for rho. J Cell Sci 1 April 1998; 111 (7): 941–950. doi: https://doi.org/10.1242/jcs.111.7.941
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