When myosin heads go walking

Muscle myosin II has two identical “heads” that really act more like hands, gripping and displacing actin to generate the force that makes a muscle contract. On page 481, Kad et al. show that only one of the two heads actually generates motion, but the second maximizes the length of the displacement.

Previous work showed that each step of a wild-type double-headed myosin displaces actin twice as far, with twice as much force, as a single-headed construct. In the new work, Kad and colleagues generated heterodimeric myosin with one wild-type head and one mutant head that can bind to actin weakly but cannot displace it. Optical trapping experiments show that this motor takes the same size steps as the wild type, so although maximal actin displacement requires two myosin heads, only one needs...