Brush border myosin heavy chain phosphorylation is regulated by calcium and calmodulin

AbstractMyosin from chicken intestinal brush borders is phosphorylated on its heavy chains at threonine by a kinase isolated from brush borders. In contrast to other heavy chain kinases, the brush border kinase activity is dependent on calcium and calmodulin. The partially purified preparation also phosphorylated myosin on its light chains at serine, but in a calmodulin-independent manner. Phosphorylation of the light chains in the absence of calmodulin or both heavy and light chains in the presence of calmodulin activated its actinactivated ATPase activity about 10-fold, to about 50 nmolmin per mg

Phosphorylation of brush border myosin at threonine on its 20 kDa light chains by a calmodulin-independent kinase activates its ATPase

AbstractA calmodulin-independent kinase isolated from chicken intestinal brush border phosphorylates brush border myosin mainly at an apparently single threonine on its 20 kDa light chains. Phosphorylation to 1.9 mol phosphate/mol myosin activated the myosin actin-activated ATPase about 12-fold, to about 100 nmol/min per mg. Brush border myosin ATPase can thus be activated by phosphorylation either at threonine, by calmodulin-independent kinase, or at serine, by calmodulin-dependent myosin light chain kinase, as previously shown [(1987) FEBS Lett. 223, 262–266]

Calmodulin dissociation regulates Myo5 recruitment and function at endocytic sites

The type I myosin Myo5 promotes actin-dependent membrane remodelling. Calmodulin binds to Myo5 and maintains it in a closed and inactive conformation. Calmodulin dissociation from Myo5 leads to local activation of actin polymerization