Human myosin-IXb is a mechanochemically active motor and a GAP for rho.

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.
Mesh Terms:
Actins, Adenosine Triphosphate, Alternative Splicing, Amino Acid Sequence, Animals, Calcium, Calmodulin, GTP Phosphohydrolases, GTP-Binding Proteins, GTPase-Activating Proteins, Humans, Leukocytes, Molecular Sequence Data, Muscle Contraction, Myosins, Protein Binding, Proteins, Rats, ras GTPase-Activating Proteins, ras Proteins, rho GTP-Binding Proteins
J. Cell. Sci.
Date: Apr. 01, 1998
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