Characterization of Recombinant Heavy Meromyosin of Physarum Polycepharum

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Background & Aims : Myosin II is a typical motor protein and is classified either as non-regulated myosin, for example, skeletal muscle myosin, or as myosin regulated by phosphorylation or Ca-binding. Myosin II from Physarum polycephalum is a Ca-binding myosin. Although expression of myosin II as a recombinant protein is essential for the analysis of its structure, function and regulation, it is not easy. Successful examples are smooth muscle myosin II and Dictyostelium myosin II, both of which are regulated by phosphorylation. Myosin II regulated by Ca-binding has not yet been obtained. Here, I report the expression of heavy meromyosin (HMM), i.e., the motor domain of Physarum myosin II. Method : I used baculovirus expression system. Sf9 cells were infected with the virus constructs. Results and Conclusions : The recombinant HMM showed basal Mg2+-ATPase activity, which was activated by actin to a similar extent to native myosin purified from Physarum. Ca-binding activity of HMM was also comparable to that of the native myosin. In vitro motility assay showed that motor activity of HMM was sensitive to Ca2+. The present study is the first report of expression of the motor domain of a myosin II that is regulated by Ca-binding.