| Abstract
| - Myosin is a repetitive impeller of actin, using its catalysis of ATP hydrolysis to derive repeatedlythe required free energy decrements. In each impulsion, changes at the myosin active site are transmittedthrough a series of structural elements to the myosin propeller (lever arm), almost 5 nm away. While thenature of transmission through most elements is evident, that through the so-called converter is not. Toinvestigate how the converter changes linear displacement into rotation, we tested (one at a time) theeffect of two Phe residue mutations (at 721 and 775) in the converter on the overall function of a heavymeromyosin (or subfragment 1) system, after first showing by observing kinetic behaviors that neithermutation affects other elements in the transmission. Using three tests (direct movement of the lever arm,activity in a motility assay with actin filaments, and direct force measurement of lever arm function), wefound that these mutations affected only movements of the converter and the lever arm. From interpretingour observations in terms of the structure of the converter, we deduce that the linear−rotationaltransformation in the converter is mediated by a little machine (two Phe residues linked to a Gly) withina machine.
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