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Divergent regulation of GIRK1 and GIRK2 subunits of the neuronal G protein gated K + channel by Gα i GDP and Gβγ
Author(s) -
Rubinstein Moran,
Peleg Sagit,
Berlin Shai,
Brass Dovrat,
KerenRaifman Tal,
Dessauer Carmen W.,
Ivanina Tatiana,
Dascal Nathan
Publication year - 2009
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2009.173229
Subject(s) - homomeric , g protein coupled inwardly rectifying potassium channel , xenopus , g protein , protein subunit , microbiology and biotechnology , g beta gamma complex , gating , biology , chemistry , heterotrimeric g protein , biophysics , biochemistry , signal transduction , gene
G protein activated K + channels (GIRK, Kir3) are switched on by direct binding of Gβγ following activation of G i/o proteins via G protein‐coupled receptors (GPCRs). Although Gα i subunits do not activate GIRKs, they interact with the channels and regulate the gating pattern of the neuronal heterotetrameric GIRK1/2 channel (composed of GIRK1 and GIRK2 subunits) expressed in Xenopus oocytes. Coexpressed Gα i3 decreases the basal activity ( I basal ) and increases the extent of activation by purified or coexpressed Gβγ. Here we show that this regulation is exerted by the ‘inactive’ GDP‐bound Gα i3 GDP and involves the formation of Gα i3 βγ heterotrimers, by a mechanism distinct from mere sequestration of Gβγ‘away’ from the channel. The regulation of basal and Gβγ‐evoked current was produced by the ‘constitutively inactive’ mutant of Gα i3 , Gα i3 G203A, which strongly binds Gβγ, but not by the ‘constitutively active’ mutant, Gα i3 Q204L, or by Gβγ‐scavenging proteins. Furthermore, regulation by Gα i3 G203A was unique to the GIRK1 subunit; it was not observed in homomeric GIRK2 channels. In vitro protein interaction experiments showed that purified Gβγ enhanced the binding of Gα i3 GDP to the cytosolic domain of GIRK1, but not GIRK2. Homomeric GIRK2 channels behaved as a ‘classical’ Gβγ effector, showing low I basal and strong Gβγ‐dependent activation. Expression of Gα i3 G203A did not affect either I basal or Gβγ‐induced activation. In contrast, homomeric GIRK1* (a pore mutant able to form functional homomeric channels) exhibited large I basal and was poorly activated by Gβγ. Expression of Gα i3 GDP reduced I basal and restored the ability of Gβγ to activate GIRK1*, like in GIRK1/2. Transferring the unique distal segment of the C terminus of GIRK1 to GIRK2 rendered the latter functionally similar to GIRK1*. These results demonstrate that GIRK1 containing channels are regulated by both Gα i3 GDP and Gβγ, while GIRK2 is a Gβγ‐effector insensitive to Gα i3 GDP .