Kinetics of Folding of the Myosin Rod

Abstract

The kinetics of the unfolding and refolding of the myosin rod have been studied by fluorescence and circular dichroism techniques, at different concentrations of protein and guanidine hydrochloride. The unfolding of the myosin rod was fast and at least biphasic in 2-3 M denaturant, with an initial immediate phase followed by a slower low-amplitude first-order phase. The refolding of the rod in 0.4-2 M guanidine hydrochloride was also at least biphasic; an initial immediate phase preceded a slow second-order phase. At the final denaturant concentration of 0.8 M, the amplitude of the burst phase was weakly dependent on the protein concentration and the rate constant of the refolding slow phase was optimal. These data are incorporated into a folding mechanism with at least three states. The high rates of the first steps of unfolding and refolding may be relevant for the functioning of the native myosin molecule by allowing a transient separation of the two strands of the myosin tail.