Myosin light chain phosphatase targeting

In addition to the displacement of caldesmon, smooth muscle cell contraction requires kinase-induced phosphorylation of myosin. Smooth muscle has a unique type of myosin filament called p-light chains which are the target (substrate) for MLCK, but MLCK is only active when complexed with CaCM. Myosin light chain phosphatase reverses the PKA-mediated process and when cytosolic calcium ion concentration falls, CDM is released from CaCM and re-associates with the actin. The central role of calcium-calmodulin in smooth muscle contraction is shown in Figure 7.4. 

Sobieszek A, Babiychuk EB, Ortner B, Borkowski J (1997a) Purification and characterization of a kinase-associated myofibriOar smooth muscle myosin light chain phosphatase possessing a calmodulin-targeting subunit. J Biol Chem 272 7027-7033... 

The effects of RhoA activity on spine number and morphology are mediated, at least in part, by the RhoA effector, Rho kinase (Nakayama et al., 2000 Tashiro and Yuste, 2004 Yuste and Bonhoeffer, 2004). Different targets of Rho-kinase have been identified, such as LIMK, myosin light chain (MLC), and MLC phosphatase. Rho-kinase phosphorylates and activates LIMK, which in turn phosphorylates and inactivates the actin depolymerization factor (ADF) cofilin (Maekawa et al., 1999 Sumi et al., 1999 Ohashi et al., 2000 Amano et al., 2001). Phosphorylation of MLC by Rho-kinase results in the stimulation of myosin-actin interactions (Amano et al.,... 

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