This basic science study demonstrates an inverse interaction between tropomyosin and phosphorylated myosin that is modulated by caldesmon.
These in vitro interactions are hypothesis-generating for smooth muscle contractility; leaves open clinical translation in cardiovascular disease.
In the present study, co-sedimentation assay, intrinsic fluorescence intensity measurement, and Mg²⁺-ATPase activity analysis were carried out to investigate the direct effect of tropomyosin (TM) on unphosphorylated myosin (UM) or phosphorylated myosin (PM) in the presence or absence of caldesmon (CaD). Results showed that TM significantly decreased the sedimentation, intrinsic fluorescence intensity, and the Mg²⁺-ATPase activity of PM, but not UM. In the presence of CaD, TM also significantly decreased these parameters irrespective of myosin phosphorylation, suggesting that the interaction between TM and CaD abolished the effects of TM on PM or UM and that there was an inverse interaction between TM and PM, characterized by the decreased PM sedimentation and intrinsic fluorescence intensity.
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Zhang et al. (2013) studied this question.
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