Hybrid and non-hybrid actomyosins reconstituted with actin, myosin and tropomyosin from skeletal and catch muscles

In this study, we investigated hybrid and non-hybrid actomyosin models including key contractile proteins: actin, myosin, and tropomyosin. These proteins were isolated from the rabbit skeletal muscle and the catch muscle of the mussel Crenomytilus grayanus. Our results confirmed literature data on an unusual ability of bivalve's tropomyosin to inhibit Mg-ATPase activity of skeletal muscle actomyosin. We have shown that the degree of inhibition depends on the environmental conditions and may vary within a wide range. The inhibitory effect of mussel tropomyosin was not detected in non-hybrid model (mussel myosin + mussel actin + mussel tropomyosin). This effect was revealed only in hybrid models containing mussel tropomyosin + rabbit (or mussel) actin + rabbit myosin. We assume that mussel and rabbit myosins have mismatched binding sites for actin. In addition, mussel tropomyosin interacting with actin is able to close the binding sites of rabbit myosin with actin, which leads to inhibition of Mg-ATPase activity.