MYOSIN MOTORS WITH ARTIFICIAL LEVER ARMS

The myosin head consists of a globular catalytic domain and a light ch ain binding domain (LCBD). The coupling efficiency between ATP hydroly sis and myosin-induced actin movement is known to decline as the LCBD is truncated or destabilized. However, it was not clear whether the ob served alteration in the production of force and movement reflects onl y the mechanical changes to the length of the LCBD or whether these ch anges also affect the kinetic properties of the catalytic domain, Here we show that replacement of the LCBD with genetically engineered doma ins of similar rigidity and dimensions produces functional molecular m otors with unchanged kinetic properties, The resulting single-chain, s ingle-headed motors were produced in Dictyostelium discoideum and obta ined after purification from a standard peptone-based growth medium at levels of up to 12 mg/l, Their actin motility properties are similar or greater than those of native myosin, Rates of 2.5 and 3.3 mu m/s we re observed for motor domains fused to one or two of these domains, re spectively, Their kinetic and functional similarity to the extensively studied myosin subfragment 1 (S1) and their accessibility to molecula r genetic approaches makes these simple constructs ideal models for th e investigation of chemo-mechanical coupling in the myosin motor.