Key result
Mutation of the GIRK1 C-terminal residue I331R or deletion of residues 330-384 disrupted the association between N- and C-termini and significantly decreased channel function.
The hydrophobic region of the GIRK1 subunit C-terminus is critical for interaction between adjacent termini and permissive for channel gating, providing insight into the structural requirements for inward rectifier function.
Findings remain preclinical; leaves open whether GIRK1 C-terminal mutations affect human cardiac or neuronal function.
The subfamily of G-protein-linked inwardly rectifying potassium channels (GIRKs) is coupled to G-protein receptors throughout the CNS and in the heart. We used mutational analysis to address the role of a specific hydrophobic region of the GIRK1 subunit. Deletion of the GIRK1 C-terminal residues 330-384, as well as the point mutation I331R, resulted in a decrease in channel function when coexpressed with GIRK4 in oocytes and in COS-7 cells. Surface protein expression of GIRK1 I331R coexpressed with GIRK4 was comparable with wild type, indicating that subunits assemble and are correctly localized to the membrane. Subsequent mutation of homologous residues in both the GIRK4 subunit and Kir2.1 (Gbetagamma-independent inward rectifier) also resulted in a decrease in channel function. Intracellular domain associations resulted in the coimmunoprecipitation of the GIRK1 N and C termini and GIRK4 N and C termini. The point mutation I331R in the GIRK1 C terminus or L337R in the GIRK4 C terminus decreased the association between the N and C termini. Mutation of a GIRK1 N-terminal hydrophobic residue, predicted structurally to interact with the C-terminal domain, also resulted in a decrease in channel function and termini association. We hypothesize that the hydrophobic nature of this GIRK1 subunit region is critical for interaction between adjacent termini and is permissive for channel gating. In addition, the homologous mutation in cytoplasmic domains of Kir2.1 (L330R) did not disrupt association, suggesting that the overall structural integrity of this region is critical for inward rectifier function.
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Sarac et al. (2005) studied this question. GIRK1 subunit mutations (I331R and deletion 330-384) vs. Wild-type GIRK1 subunit was evaluated on Channel function (peak high-K+ and carbachol-induced currents). Mutation of the GIRK1 C-terminal residue I331R or deletion of residues 330-384 disrupted the association between N- and C-termini and significantly decreased channel function.
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