Non-basic amino acids in the ROMK1 channels via an appropriate distance modulate PIP2 regulated pHi-gating

Simulating PIP2-Induced Gating Transitions in Kir6.2 Channels

ATP-sensitive potassium (KATP) channels consist of an inwardly rectifying K+ channel (Kir6.2) pore, to which four ATP-sensitive sulfonylurea receptor (SUR) domains are attached, thereby coupling K+ permeation directly to the metabolic state of the cell. Dysfunction is linked to neonatal diabetes and other diseases. K+ flux through these channels is controlled by conformational changes in the helix bundle region, which acts as a physical barrier for K+ permeation. In addition, the G-loop, located in the cytoplasmic domain, and the selectivity filter might contribute to gating, as suggested by different disease-causing mutations. Gating of Kir channels is regulated by different ligands, like Gβγ, H+, Na+, adenosine nucleotides, and the signaling lipid phosphatidyl-inositol 4,5-bisphosphate (PIP2), which is an essential activator for all eukaryotic Kir family members. Although molecular determinants of PIP2 activation of KATP channels have been investigated in functional studies, structural information of the binding site is still lacking as PIP2 could not be resolved in Kir6.2 cryo-EM structures. In this study, we used Molecular Dynamics (MD) simulations to examine the dynamics of residues associated with gating in Kir6.2. By combining this structural information with functional data, we investigated the mechanism underlying Kir6.2 channel regulation by PIP2.

Dynamic role of the tether helix in PIP2-dependent gating of a G protein-gated potassium channel

G protein–gated inwardly rectifying potassium (GIRK) channels are activated by the phospholipid phosphatidylinositol 4,5 bisphosphate (PIP₂). Using functional and computational experiments, Lacin et al. reveal that PIP₂ interacts with the tether helix of the neuronal GIRK channel in a dynamic way.

G protein–gated inwardly rectifying potassium (GIRK) channels control neuronal excitability in the brain and are implicated in several different neurological diseases. The anionic phospholipid phosphatidylinositol 4,5 bisphosphate (PIP₂) is an essential cofactor for GIRK channel gating, but the precise mechanism by which PIP₂ opens GIRK channels remains poorly understood. Previous structural studies have revealed several highly conserved, positively charged residues in the “tether helix” (C-linker) that interact with the negatively charged PIP₂. However, these crystal structures of neuronal GIRK channels in complex with PIP₂ provide only snapshots of PIP₂’s interaction with the channel and thus lack details about the gating transitions triggered by PIP₂ binding. Here, our functional studies reveal that one of these conserved basic residues in GIRK2, Lys200 (6′K), supports a complex and dynamic interaction with PIP₂. When Lys200 is mutated to an uncharged amino acid, it activates the channel by enhancing the interaction with PIP₂. Atomistic molecular dynamic simulations of neuronal GIRK2 with the same 6′ substitution reveal an open GIRK2 channel with PIP₂ molecules adopting novel positions. This dynamic interaction with PIP₂ may explain the intrinsic low open probability of GIRK channels and the mechanism underlying activation by G protein Gβγ subunits and ethanol.