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

Abstract

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.