Isoform diversity, regulation, and functional adaptation of troponin and calponin.

Actin-activated myosin II motor function powers muscle contraction and nonmuscle cell motility. The actin-myosin-derived contractility has evolved with a great diversity in different muscle and cell types. Actin filament-based regulation controls striated muscle contraction and plays a role in modulating smooth muscle contractility and nonmuscle cell motility. This review focuses on the isoform diversity and functional adaptations of troponin in striated muscle and calponin in smooth muscle and nonmuscle cells. The gene regulation, alternative RNA splicing, and posttranslational modifications of troponin I and troponin T are summarized, together with recent progress in calponin studies. The biologic significance of the structural and functional diversity and regulation of troponin and calponin is discussed for roles in normal contractility and diseases.