Journal Article

X-ray structure of the mammalian GIRK2–βγ G-protein complex

MacKinnon, Roderick, Whorton, Matthew R.

2013

Overview

G-protein-gated inward rectifier K + (GIRK) channels allow neurotransmitters, through G-protein-coupled receptor stimulation, to control cellular electrical excitability. In cardiac and neuronal cells this control regulates heart rate and neural circuit activity, respectively. Here we present the 3.5 Å resolution crystal structure of the mammalian GIRK2 channel in complex with βγ G-protein subunits, the central signalling complex that links G-protein-coupled receptor stimulation to K + channel activity. Short-range atomic and long-range electrostatic interactions stabilize four βγ G-protein subunits at the interfaces between four K + channel subunits, inducing a pre-open state of the channel. The pre-open state exhibits a conformation that is intermediate between the closed conformation and the open conformation of the constitutively active mutant. The resultant structural picture is compatible with ‘membrane delimited’ activation of GIRK channels by G proteins and the characteristic burst kinetics of channel gating. The structures also permit a conceptual understanding of how the signalling lipid phosphatidylinositol-4,5-bisphosphate (PIP 2 ) and intracellular Na + ions participate in multi-ligand regulation of GIRK channels. An X-ray structure and electrophysiological analysis of mammalian G-protein-gated inward rectifier potassium channel GIRK2 in complex with βγ reveals a pre-open channel structure consistent with channel activation by membrane delimited G-protein subunits. GIRK2–G-protein βγ dimer structure The activation of G-protein-coupled receptors (GPCRs) leads to the release of the G-protein subunits Gα and Gβγ from the intracellular surface of the GPCR. Gβγ can then bind to, and activate, the G-protein-gated inward rectifier K + (GIRK) channel, causing the channel pore to open. The opening of GIRK channels drives the membrane voltage towards the resting (Nernst) potential, which slows the rate of membrane depolarization. In this manuscript, Matthew Whorton and Roderick MacKinnon solve the X-ray crystal structure of a mammalian GIRK2 channel in the presence of the βγ G-protein subunits. Although the overall structure of the βγ G-protein subunits is essentially the same in the presence of Gα or GIRK, the structures of GIRK and GIRK–Gβγ are quite different. The structure also reveals how the signalling lipid PIP2 and intracellular Na + ions help to regulate the activity of GIRKs.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 631/45/269/1151 / 631/535/1266 / 631/57/2270/1140 / 631/92/612/194 / Binding Sites / Crystallography, X-Ray / G Protein-Coupled Inwardly-Rectifying Potassium Channels - chemistry / G Protein-Coupled Inwardly-Rectifying Potassium Channels - genetics / G Protein-Coupled Inwardly-Rectifying Potassium Channels - metabolism / Heterotrimeric GTP-Binding Proteins - chemistry / Heterotrimeric GTP-Binding Proteins - genetics / Heterotrimeric GTP-Binding Proteins - metabolism / Humanities and Social Sciences / Humans / Ion Channel Gating / Models, Biological / Models, Molecular / multidisciplinary / Phosphatidylinositol 4,5-Diphosphate - metabolism / Protein Conformation / Protein Interaction Domains and Motifs / Protein Subunits - chemistry / Protein Subunits - metabolism / Science / Sodium - metabolism / Static Electricity