Introduction

Calmodulin is a Ca binding protein. it consists of four so called EF hand motifs which provide a ASP containing framework to bind Ca ions.
upon binding of the Ca the protein undergoes remarkable conformational changes. this changes provide a hydrophobic anchor site to bind other proteins and activating them. this activation leads to varying physiological responses based on activated protein.
Calmodulin as a Ca regulator
As we do know Ca concentration must be regulated in cytosol. this regulation occurs when high concentration of calcium is in cytosol. when cytosolic ca concentration increases it binds to calmodulin. in turn activated calmodulin makes contact with specific plasma membrane ca ion pump. this may lead to activation of the pump and subsequent ca concentration decrease in cytosol.
smooth muscle activation
activated calmodulin also induces smooth muscle contraction. calmodulin does this in two pathway:
1)Binding to specific protein called caldesmon. this protein when not bound to calmodulin, binds to actin filaments and inhibits muscle contraction.
2)activate a specifc CaM Kinase which phosphorylates light chain of myosin and activates myosin.