Motility of myosin V regulated by the dissociation of single calmodulin

Myosin V is a calmodulin-binding motor protein. The dissociation of single calmodulin molecules from individual myosin V molecules at 1 muM Ca2+ correlates with a reduction in sliding velocity in an in vitro motility assay. The dissociation of two calmodulin molecules at 5 muM Ca2+ correlates with a detachment of actin filaments from myosin V. To mimic the regulation of myosin V motility by Ca2+ in a cell, caged Ca2+ coupled with a UV flash system was used to produce Ca2+ transients. During the Ca2+ transient, myosin V goes through the functional cycle of reduced sliding velocity, actin detachment and reattachment followed by the recovery of the sliding velocity. These results indicate that myosin V motility is regulated by Ca2+ through a reduction in actin-binding affinity resulting from the dissociation of single calmodulin molecules.