Dissection of the difference between the group I metal ions in inhibiting GSK3β: a computational study

Glycogen synthase kinase 3β (GSK3β) is a serine/threonine kinase that requires two cofactor Mg2+ ions for catalysis in regulating many important cellular signals. Experimentally, Li+ is a competitive inhibitor of GSK3β relative to Mg2+, while this mechanism is not experienced with other group I metal ions. Herein, we use native Mg22+–Mg12+ GSK3β and its Mg22+–M1+ (M = Li, Na, K, and Rb) derivatives to investigate the effect of metal ion substitution on the mechanism of inhibition through two-layer ONIOM-based quantum mechanics/molecular mechanics (QM/MM) calculations and molecular dynamics (MD) simulations. The results of ONIOM calculations elucidate that the interaction of Na+, K+, and Rb+ with ATP is weaker compared to that of Mg2+ and Li+ with ATP, and the critical triphosphate moiety of ATP undergoes a large conformational change in the Na+, K+, and Rb+ substituted systems. As a result, the three metal ions (Na+, K+, and Rb+) are not stable and depart from the active site, while Mg2+ and Li+ can stabilize in the active site, evident in MD simulations. Comparisons of Mg22+–Mg12+ and Mg22+–Li1+ systems reveal that the inline phosphor-transfer of ATP and the two conserved hydrogen bonds between Lys85 and ATP, together with the electrostatic potential at the Li1+ site, are disrupted in the Mg22+–Li1+ system. These computational results highlight the possible mechanism why Li+ inhibits GSK3β.