Head of myosin IX binds calmodulin and moves processively toward the plus-end of actin filaments.
Mammalian myosin IXb (Myo9b) has been shown to exhibit unique motor properties in that it is a single-headed processive motor and the rate-limiting step in its chemical cycle is ATP hydrolysis. Furthermore, it has been reported to move toward the minus- and the plus-end of actin filaments. To analyze the contribution of the light chain-binding domain to the movement, processivity, and directionality of a single-headed processive myosin, we expressed constructs of Caenorhabditis elegans myosin IX (Myo9) containing either the head (Myo9-head) or the head and the light chain-binding domain (Myo9-head-4IQ). Both constructs supported actin filament gliding and moved toward the plus-end of actin filaments. We identified in the head of class IX myosins a calmodulin-binding site at the N terminus of loop 2 that is unique among the myosin superfamily members. Ca(2+)/calmodulin negatively regulated ATPase and motility of the Myo9-head. The Myo9-head demonstrated characteristics of a processive motor in that it supported actin filament gliding and pivoting at low motor densities. Quantum dot-labeled Myo9-head moved along actin filaments with a considerable run length and frequently paused without dissociating even in the presence of obstacles. We conclude that class IX myosins are plus-end-directed motors and that even a single head exhibits characteristics of a processive motor.
Institute of Molecular Cell Biology, Westfalian Wilhelms-University, 48149 Münster, Germany.
Wanqin
W
Liao
Kerstin
K
Elfrink
Martin
M
Bähler
D000199:Actins / Q000737:chemistry*; D000251:Adenosine Triphosphatases / Q000737:chemistry; D000818:Animals; D017173:Caenorhabditis elegans; D002118:Calcium / Q000737:chemistry; D002147:Calmodulin / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D013058:Mass Spectrometry / Q000379:methods; D009218:Myosins / Q000737:chemistry*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D045663:Quantum Dots; D011994:Recombinant Proteins / Q000737:chemistry
D000199:Actins; D002147:Calmodulin; D011994:Recombinant Proteins; C113469:myosin IXB; D000251:Adenosine Triphosphatases; D009218:Myosins; D002118:Calcium