Structural studies of the Na+/Ca2+ exchanger by high-resolution nuclear magnetic resonance spectroscopy

Abstract

Na+/Ca2+ exchangers (NCX) are membrane proteins that use the electrochemical gradient of Na+ to remove Ca2+ from the cytosol. They are essential for the maintenance of the intracellular Ca2+ homeostasis in various cell types, especially in excitable cells. CALX, the Na+/Ca2+ exchanger from Drosophila melanogaster, is found in sensory neuronal cells. It displays a unique regulatory behavior because it is inhibited instead of activated by intracellular Ca2+ as all other eukaryotic exchangers. The aim of this proposal is to investigate the structure of the CALX, and the mechanism of allosteric regulation of this exchanger. We will use NMR spectroscopy as the main technique. Specifically, the aims of the present proposal are: i) to characterize the oligomerization state and the functionality of the Na+/Ca2+ exchanger from the hyperthermophilic archaea Methanococcus janaschii, isolated in the presence of detergent micelles; ii) to investigate in atomic detail the mechanism of the CALX allosteric regulation by intracellular Ca2+. With respect to the latter, we will use solution NMR spectroscopy and isothermal titration calorimetry (ITC) to study soluble fragments of the exchanger in the absence and presence of Ca2+. We will also carry out Ca2+ transport assays with the full-length exchanger and mutants in cell. (AU)