A double bilayer to study the nonequilibrium environmental response of GIRK2 in complex states

Abstract

G protein-gated inwardly rectifying potassium (GIRK) channels play essential roles in electrical signaling in neurons and muscle cells. Nonequilibrium environments provide crucial driving forces behind many cellular events. Here, we apply the antiparallel alignment double bilayer model to study GIRK2 in response to the time-dependent membrane potential. Using molecular dynamics and umbrella sampling, we examined the time-dependent environmental impact on the ion conduction, energy basis, and primary motions of GIRK2 in different complex states with phosphatidylinositol-4,5-bisphosphate (PIP₂) and G-protein βγ subunits (Gβγ). The antiparallel alignment double bilayer model enables us to study the transport performance in inward and outward K⁺ and mixed K⁺ and Na⁺. We obtained the recoverable discharge process of GIRK2 complexed with both PIP₂ and Gβγ, compared with occasional conduction under PIP₂-only regulation. Calculations of potential of mean force suggest different regulation by the helix bundle crossing (HBC) gate and G-loop gate regarding different complex states and under a membrane potential. In a nonequilibrium environment, distinct functional rocking motions of GIRK2 were identified under strengthened correlations between the transmembrane helices and downstream cytoplasmic domains with binding of PIP2, cations, and Gβγ. The findings suggest the potential domain motions and dynamics associated with a nonequilibrium environment and highlight the application of the antiparallel alignment double bilayer model to investigate factors in an asymmetric environment.