Which protein regulates myosin activity in smooth muscle contraction?
Smooth muscle lacks troponin placing regulation directly on myosin thick filament via calcium sensing protein calmodulin small acidic protein essential for many signaling pathways. Calmodulin is 17 kDa dumbbell protein with four EF hand calcium binding loops two in each lobe. Apo calmodulin inactive at low calcium. Calcium rise induced by cholinergic stimulation and IP3 mediated sarcoplasmic release saturates calmodulin to Ca4 calmodulin exposing methionine rich hydrophobic grooves that wrap around autoinhibitory sequence of myosin light chain kinase MLCK displacing it from substrate binding s
Ref: Webster et al., J Physiol; Kamm & Stull Physiol Rev – Calmodulin regulation of smooth muscle myosin via MLCK.