Inhibition of carnitine acetyltransferase by mildronate, a regulator of energy metabolism

Abstract

Carnitine acetyltransferase (CrAT; EC 2.3.1.7) catalyzes the reversible transfer of acetyl groups between acetyl-coenzyme A (acetyl-CoA) and L-carnitine; it also regulates the cellular pool of CoA and the availability of activated acetyl groups. In this study, biochemical measurements, saturation transfer difference (STD) nuclear magnetic resonance (NMR) spectroscopy, and molecular docking were applied to give insights into the CrAT binding of a synthetic inhibitor, the cardioprotective drug mildronate (3-(2,2,2-trimethylhydrazinium)-propionate). The obtained results show that mildronate inhibits CrAT in a competitive manner through binding to the carnitine binding site, not the acetyl-CoA binding site. The bound conformation of mildronate closely resembles that of carnitine except for the orientation of the trimethylammonium group, which in the mildronate molecule is exposed to the solvent. The dissociation constant of the mildronate CrAT complex is approximately 0.1 mM, and the K_i is 1.6 mM. The results suggest that the cardioprotective effect of mildronate might be partially mediated by CrAT inhibition and concomitant regulation of cellular energy metabolism pathways.

Keywords::

• Carnitine acetyltransferase
• acetyl-CoA
• mildronate
• STD NMR
• inhibition

Acknowledgements

We would like to thank Dr. L. Fielding (Organon Laboratories Ltd, UK) for assistance with binding curve fitting procedures.

Declaration of interest: This study was supported by a grant from the Latvian Science Council (05.1461) and Latvian State Research Program “New medicines and biocorrection tools: design, transport forms and mechanisms of action.”