Calcium (Ca) is perhaps the most important messenger for the control of intracellular events. The action of Ca is mediated by Ca binding proteins (CBP). Calmodulin (CDR) appears to be the most universal CBP and it is directly involved in the regulation of a wide variety of Ca dependent events including: smooth muscle contraction, neurosecretion, cell proliferation and cell-cell interactions. In the presence of Ca, CDR binds to the proteins it activates, producing structural changes and activation of each protein. Presently, it is unclear how CDR mediates so many Ca dependent processes with such apparent harmony. Recently, we have demonstrated that some of the 3-4 drug binding sites on CDR are allosterically related and that drug binding to some sites can potentiate drug binding to other sites. We will continue our development of methods to monitor the interaction of drugs and various purified calmodulin binding proteins with calmodulin. We will determine which of these proteins are activated by binding to the same (or different) binding sites on calmodulin and determine the allosteric relationships among drug and protein binding sites. Our proposed studies with proteolytic fragments of calmodulin should allow us to more accurately map the regions of calmodulin which serve as the interfacial site for various drug and protein binding. We will determine if the allosteric mechanism that we have observed among drug binding sites on calmodulin occurs among protein binding sites on calmodulin. Further, we will determine if this allosteric mechanism is capable of regulating the interaction of purified calmodulin with myosin light chain kinase and of regulating tension in chemically skinned smooth muscle. We feel that these allosteric control mechanisms on calmodulin can perhaps explain how this """"""""universal"""""""" Ca dependent regulatory protein is directed towards the activation of more than twenty different proteins with any degree of specificity. These studies should increase our understanding of the mechanism of action of calmodulin and of Ca binding proteins in general since allosteric regulatory mechanisms exist among the drug (and protein) binding sites of skeletal and cardiac troponin C and in the voltage dependent Ca channel of muscle.
