Key result
ITC and NMR analyses revealed that four Gβγ molecules bind to a tetramer of the GIRK cytoplasmic pore with a dissociation constant of 250 μM, spanning two neighboring subunits.
Effect estimate: Kd 250 μM
This basic science study elucidates the structural mechanism of GIRK channel gating by Gβγ subunits, which is fundamental to understanding heart rate regulation.
Clarifies Gβγ-GIRK stoichiometry in vitro; leaves open relevance to native cardiac channel function and heart rate control.
G protein-activated inwardly rectifying potassium channel (GIRK) plays crucial roles in regulating heart rate and neuronal excitability in eukaryotic cells. GIRK is activated by the direct binding of heterotrimeric G protein βγ subunits (Gβγ) upon stimulation of G protein-coupled receptors, such as M2 acetylcholine receptor. The binding of Gβγ to the cytoplasmic pore (CP) region of GIRK causes structural rearrangements, which are assumed to open the transmembrane ion gate. However, the crucial residues involved in the Gβγ binding and the structural mechanism of GIRK gating have not been fully elucidated. Here, we have characterized the interaction between the CP region of GIRK and Gβγ, by ITC and NMR. The ITC analyses indicated that four Gβγ molecules bind to a tetramer of the CP region of GIRK with a dissociation constant of 250 μM. The NMR analyses revealed that the Gβγ binding site spans two neighboring subunits of the GIRK tetramer, which causes conformational rearrangements between subunits. A possible binding mode and mechanism of GIRK gating are proposed.
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Yokogawa et al. (2010) studied this question. Gβγ binding to GIRK1 cytoplasmic pore was evaluated on Dissociation constant and binding site characterization (Kd 250 μM). ITC and NMR analyses revealed that four Gβγ molecules bind to a tetramer of the GIRK cytoplasmic pore with a dissociation constant of 250 μM, spanning two neighboring subunits.
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