Two heads of myosin are better than one for generating force and motion

Several classes of the myosin superfamily are distinguished by their "doubl e-headed" structure, where each head is a molecular motor capable of hydrol yzing ATP and interacting with actin to generate force and motion. The func tional significance of this dimeric structure, however, has eluded investig ators since its discovery in the Late 1960s, Using an optical-trap transduc er, we have measured the unitary displacement and force produced by double- headed and single-headed smooth- and skeletal-muscle myosins. Single-headed myosin produces approximately half the displacement and force (approximate to 6 nm; 0.7 pN) of double-headed myosin (approximate to 10 nm; 1.4 pN) du ring a unitary interaction with actin, These data suggest that muscle myosi ns require both heads to generate maximal force and motion.