Purification, crystallization and preliminary X-ray diffraction of the N-terminal calmodulin-like domain of the human mitochondrial ATP-Mg/P_i carrier SCaMC1

SCaMC is an ATP-Mg/P_i carrier protein located at the mitochondrial inner membrane. SCaMC has an unusual N-terminal Ca²⁺-binding domain (NTD) in addition to its characteristic six-helix transmembrane bundle. The NTD of human SCaMC1 (residues 1–193) was expressed and purified in order to study its role in Ca²⁺-regulated ATP-Mg/P_i transport mediated by its transmembrane domain. While Ca²⁺-bound NTD could be crystallized, the apo state resisted extensive crystallization trials. Selenomethionine-labeled Ca²⁺-bound NTD crystals, which belonged to space group P6₂22 with one molecule per asymmetric unit, diffracted X-rays to 2.9 Å resolution.