A region of the sulfonylurea receptor critical for a modulation of ATP-sensitive K⁺ channels by G-protein βγ-subunits

To determine the interaction site(s) of ATP-sensitive K⁺ (K(ATP)) channels for G-proteins, sulfonylurea receptor (SUR2A or SUR1) and pore-forming (Kir6.2) subunits were reconstituted in the mammalian cell line, COS-7. Intracellular application of the G-protein βγ2-subunits (G(βγ2)) caused a reduction of ATP-induced inhibition of Kir6.2/SUR channel activities by lessening the ATP sensitivity of the channels. G(βγ2) bound in vitro to both intracellular (loop-NBD) and C-terminal segments of SUR2A, each containing a nucleotide-binding domain (NBD). Furthermore, a single amino acid substitution in the loop-NBD of SUR (Arg656A1a in SUR2A or Arg665A1a in SUR1) abolished the G(βγ2)-dependent alteration of the channel activities. These findings provide evidence that G(βγ) modulates K(ATP) channels through a direct interaction with the loop-NBD of SUR.