title: Human myosin-IXb is a mechanochemically active motor and a GAP for rho.
abstract: 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.
authors.affiliation: Department of Molecular Biology, Yale University, New Haven, CT 06520, USA. penny.post@yale.edu
authors.forename: P L
authors.initials: PL
authors.lastname: Post
authors.forename: G M
authors.initials: GM
authors.lastname: Bokoch
authors.forename: M S
authors.initials: MS
authors.lastname: Mooseker
mesh_terms: D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D006801:Humans; D007962:Leukocytes; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects; D009218:Myosins / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D011485:Protein Binding; D011506:Proteins / Q000502:physiology*; D051381:Rats; D020703:ras GTPase-Activating Proteins; D018631:ras Proteins / Q000378:metabolism*; D020741:rho GTP-Binding Proteins
chemical_list: D000199:Actins; D002147:Calmodulin; D020690:GTPase-Activating Proteins; D011506:Proteins; C113469:myosin IXB; D020703:ras GTPase-Activating Proteins; D000255:Adenosine Triphosphate; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D009218:Myosins; D018631:ras Proteins; D020741:rho GTP-Binding Proteins; D002118:Calcium