Dictyostelium Myosin II G680V Suppressors Exhibit Overlapping Spectra of Biochemical Phenotypes Including Facilitated Phosphate Release

We have biochemically characterized 13 intragenic suppressors of the G680V mutation of Dictyostelium myosin II. In the absence of the G680V mutation, the suppressors result in a number of deviant behaviors, most commonly an increase in the basal (actin-independent) ATPase of the motor. This phenotype is complementary to that of the G680V mutant and supports our proposal that the latter impairs phosphate release. Different subsets of the mutants also suffer from poor ATPase enhancement by 1 mg/ml actin, failure to release from actin in the presence of ATPγS (or ADP and salt), and excessive release from actin in the presence of ADP. The patterns of suppressor behaviors suggest that, in general, they are facilitating Pi-releasing state(s) of the motor, but that different individual suppressors may secondarily perturb other states or actions of the motor.