Effect of Cd2+ on muscle type of creatine kinase: Inhibition kinetics integrating computational simulations.

Creatine kinase (EC 2.7.3.2, CK) plays an important role in cellular energy metabolism and homeostasis by catalyzing the transfer of phosphate between ATP and creatine phosphate. We investigated the effects of Cd2+ on muscle type of creatine kinase from Pelodiscus sinensis (PSCKM). Cd2+ conspicuously inactivated the activity of PSCKM (IC50=0.062 mM) in a first-order kinetic process and exhibited non-competitive inhibition with creatine and ATP. A conformational study showed that Cd2+ induced tertiary structure changes in PSCKM with exposure of hydrophobic surfaces. The addition of osmolytes, such as glycine and proline, partially reactivated the Cd2+-mediated inactive PSCKM. Additionally, molecular dynamics and docking simulations between PSCKM and Cd2+ were conducted to show that Cd2+ blocked the entrance of ATP to the active site, and this result is consistent with the experimental results showing Cd2+-induced inactivation of PSCKM. Our study demonstrates the effect of Cd2+ on PSCKM enzymatic function and unfolding, including the protective effects of osmolytes on PSCKM inactivation. This study provides important insights into the changes in the PSCKM metabolic enzyme of ectothermic animals in response to the environment.