Nonempirical conformational analysis of oubaine molecule chelate complexes with Ca2+ and possible mechanism of modulation of transductor function of Na+,K+-ATPhase

Complete conformational analysis of chelate complex of oubaine molecule with Ca2+ in 1:1 stoichiometry is carried out. Complete ab initio optimization of geometric parameters of all possible structures of the complexes is performed in the framework of restricted Hartree-Fock method with 6–31G* basis using GAMESS program. Influence of the complex formation on the steric structure and electronic structure of oubaine molecule is analyzed. Oubaine molecule is found capable of binding Ca2+ by two modes. Mechanism of binding of oubaine molecule with transductor site of Na+,K+-ATPhase is proposed: ligand-receptor interaction is assumed to be realized in account of formation of trial complex oubaine-Ca2+-Na+,K+-ATPhase, with main contribution to the interaction energy of ion-ion bonds formation between Ca2+ and nucleophilic functional groups in the composition of the mentioned binding site of Na+,K+-ATPhase.