The weaver mutation changes the ion selectivity of the affected inwardly rectifying potassium channel GIRK2

Abstract

The weaver mutation in mice has recently been identified as a single base-pair mutation in the Girk2 gene, which encodes a G-protein-activated inwardly rectifying potassium channel, GIRK2. The mutation results in a Gly to Ser substitution at residue 156, in the putative pore-forming region of the potassium channel. In the present study, we used Xenopus oocytes to express mutant GIRK2, and to characterize the effects of the mutation on the channel. The mutation results in a loss of the normal high selectivity for K ÷ over Na ÷, with little effect on other channel properties such as activation by the mu opioid receptor. The resulting increase in basal Na ÷ permeability causes a marked depolarization of oocytes expressing the mutant GIRK2 protein. This result was observed even when the mutant GIRK2 was coexpressed with GIRK1, a situation more analogous to that seen in vivo. Thus, the increased Na ÷ permeability and resulting depolarization may contribute to the pathology of cerebellar granule cells and substantia nigra dopaminergic neurons observed in the weaver mice.weaver mutation consists of a Gly to Ser substitution at residue 156 in the GIRK2 protein. This destroys the Gly-Tyr-Gly motif in the putative pore-forming region (H5 domain), a region that is highly conserved in several potassium channel families. It has been reported that mutations of conserved residues in the H5 domain of another potassium channel (ShB) either eliminate channel conductance or alter ion selectivity [8].

A Cell Cycle Alteration Precedes Apoptosis of Granule Cell Precursors in the Weaver Mouse Cerebellum

“…[5][6][7][8][9][10][11][12] It is generally assumed that target cells in weaver mice die as a result of chronic depolarization; however, the pathogenetic mechanisms that lead to selective activation of apoptosis in cerebellar granule cell precursors but not in dopaminergic neurons of midbrain are not completely understood. Here we show that abnormalities in the control of cell cycle in wv/wv cerebellum represent a major and early consequence of the altered GIRK2 channel function that may strongly influence the susceptibility of EGL cells to undergo apoptosis.…”

“…4 In vitro, the mutation leads to a complex series of changes in channel activity, ranging from a loss of G-proteindependent inward rectifier current regulation 5,6 to reduced selectivity for potassium over sodium and calcium ions. [7][8][9][10][11][12] This alteration results in chronic depolarization and cell death. In vivo studies show that the granule cell precursors of the external germinal layer (EGL) of the cerebellum die massively via apoptosis within the first 3 postnatal weeks.…”

An inwardly rectifying K+ channel is required for patterning

“…How broadly can these findings be applied to other K + channels? A gain-of-function GYG to SYG change in the selectivity filter of the G protein-coupled Irk2 (GIRK2) channel allows it to pass Na + and Ca 2+ , which alters cerebellar development in the weaver mouse (Rakic and Sidman, 1973;Hatten et al, 1984;Hatten et al, 1986;Patil et al, 1995;Silverman et al, 1996;Tong et al, 1996). However, deletion of GIRK2 allows mice to develop normally (Signorini et al, 1997).…”

Gain of Function Mutants: Ion Channels and G Protein-Coupled Receptors

“…We note here, but do not discuss further, that a disrupted NHE1 Na within a few angstroms, by two permeant ions (Doyle et al 1998). Although there is no crystal structure for the Gly Ͼ Ser mutant, it is apparent that this crucial mutation would change the shape of the permeation pathway, and this shape change presents an explanation, at a resolution of angstroms but perhaps not at the subangstrom level, for the general agreement that the mutated channel has altered selectivity: The wvGIRK2 channel has roughly equal permeability for Na ‫ם‬ and K ‫ם‬ , Navarro et al 1996, Slesinger et al 1996, Tong et al 1996, Tucker et al 1996, with some permeability for Ca ‫ם2‬ as well (Silverman et al 1996). A previous report shows that certain other mutations in the GYG motif of Shaker also produce a loss of selectivity (Heginbotham et al 1994).…”