Actin-based motor properties of native myosin VIIa

Myosin VIIa has critical roles in the inner ear and the retina. To help understand how this protein functions, native myosin VIIa was tested for mechanoenzymatic properties. Myosin VIIa was immunoprecipitated from retinal tissue and found to be associated with calmodulin in a Ca(2+)-sensitive manner. Myosin VIIa Mg-ATPase activity was detected; in the absence of Ca(2+) (i.e. with bound calmodulin), it was stimulated by f-actin with a K(cat) of 4.3 s(-1) and with 7 microM actin required for half-maximal activity. In a sliding filament motility assay, myosin VIIa moved actin filaments with a velocity of 190 nm s(-1). These results demonstrate that myosin VIIa is a calmodulin-binding protein and a bona fide actin-based motor.