Contractility of vascular smooth muscle depends on phosphorylation of myosin light chains, and is modulated by hormonal control of myosin phosphatase activity. Signaling pathways activate kinases such as PKC or Rho-dependent kinases that phosphorylate the myosin phosphatase inhibitor protein called CPI-17. Phosphorylation of CPI-17 at Thr-38 enhances its inhibitory potency 1000-fold, creating a molecular switch for regulating contraction [1].

1: Solution NMR structure of the myosin phosphatase inhibitor protein CPI-17 shows phosphorylation-induced conformational changes responsible for activation. Ohki S, Eto M, Kariya E, Hayano T, Hayashi Y, Yazawa M, Brautigan D, Kainosho M; J Mol Biol 2001;314:839-849. PMID:11734001