Probing the Interaction of Cisplatin with Calmodulin and its Effect upon Binding to Myosin Light-Chain Kinase

Abstract

Despite the successful clinical application of cisplatin, its mechanism of action and adverse effects remain poorly understood. To elucidate the complex pharmacology of this drug, research has focused on its interaction with proteins. Herein, we examined the interaction of cisplatin with calmodulin (CaM), a pivotal protein in signal transduction, and its effect upon binding to the MLCK kinase. Selective labeling of the proteins, including 13CH3-methionine- and 15N-labeled CaM, as well as 19F-tryptophan-labeled MLCK, enabled effective detection of protein folding and interactions using multiple NMR techniques. Results revealed that cisplatin readily reacts with CaM, leading to mobilization of bound Ca2+ ions and inhibition of CaM/MLCK complex formation. The preformed CaM/MLCK complex exhibited greater resilience to cisplatin, as compared to free CaM, due to more embedded methionine residues within the CaM/MLCK complex. Although the complex survived to platination, some destabilization occurred, as evidenced by the mobilization of some Ca2+ ions and collapse of the complex under chromatographic conditions. Analogous reactions occur in a cellular setting. These results imply that the platination of CaM could underlie the mechanism of cisplatin-induced neurotoxicity.