ABCMdb

PMID: 22802363

Pratt EB, Zhou Q, Gay JW, Shyng SL
Engineered interaction between SUR1 and Kir6.2 that enhances ATP sensitivity in KATP channels.
J Gen Physiol. 2012 Aug;140(2):175-87. doi: 10.1085/jgp.201210803. Epub 2012 Jul 16., [PubMed]

Sentences

No. Mutations Sentence Comment

24 ABCC8 p.Glu203Lys Channels bearing an E203K mutation in SUR1 and a Q52E in Kir6.2 exhibit ATP sensitivity &#e07a;100-fold higher than wild-type channels. Login to comment 25 ABCC8 p.Glu203Cys Cross-linking of E203C in SUR1 and Q52C in Kir6.2 locks the channel in a closed state and is reversible by reducing agents, demonstrating close proximity of the two residues. Login to comment 45 ABCC8 p.Glu128Lys When recording from cells expressing E128K mutant channels, the cells were pretreated with 300 &#b5;M tolbutamide overnight to augment expression, followed by a 2-h washout period. Login to comment 58 ABCC8 p.Glu203Lys We show that coexpression of a Kir6.2 with the mutation Q52E in the N-terminal domain and a SUR1 with the mutation E203K in the cytoplasmic region immediately following TMD0 yielded channels with ATP sensitivity nearly 100-fold higher than WT channels. Login to comment 86 ABCC8 p.Glu203Cys ABCC8 p.Glu203Cys Fig. S3 shows that Q52C-Kir6.2//E203C-SUR1 channels have WT-like ATP sensitivity in the absence of cross-linking. Fig. S4 shows that control channels do not cross-link in the presence of an inhibitory concentration of ATP plus oxidizing agent; it also shows that Tris(2-carboxyethyl)phosphine (TCEP) is an effective reducing agent to reverse the cross-linking within Q52C-Kir6.2//E203C-SUR1 channels. Login to comment 87 ABCC8 p.Glu128Cys Fig. S5 illustrates that Q52C-Kir6.2//E128C-SUR1 channels show no evidence of cross-linking. Fig. S6 shows MgADP stimulation of Q52E-Kir6.2 channels. Login to comment 102 ABCC8 p.Glu203Lys ABCC8 p.Lys205Glu ABCC8 p.Arg202Glu ABCC8 p.Lys199Glu Error bars represent SEM, and some are smaller than the symbols. (K199E, R202E, E203K, and K205E) and then coexpressed with WT-, Q52E-, or Q52R-Kir6.2. Login to comment 104 ABCC8 p.Lys205Glu When coexpressed with WTKir6.2, only K205E-SUR1 had an obvious effect on ATP sensitivity, causing reduced inhibition by ATP (hereinafter "//" is used to denote heteromeric Kir6.2 and SUR1 combinations and "/" is used to separate multiple mutations in a single SUR1 or Kir6.2 subunit). Login to comment 106 ABCC8 p.Arg202Glu ABCC8 p.Lys199Glu When coexpressed with Q52E-Kir6.2, the K199E- and R202E-SUR1 did not modify the effect of the Q52E-Kir6.2 mutation on ATP sensitivity. Login to comment 107 ABCC8 p.Lys205Glu ABCC8 p.Lys205Glu Combination of K205E-SUR1 and Q52E-Kir6.2 yielded channels with decreased ATP sensitivity close to that seen in WT-Kir6//K205E-SUR1 channels. Login to comment 108 ABCC8 p.Glu203Lys However, the most striking change of ATP sensitivity indicative of functional interaction was seen in channels formed by Q52E-Kir6.2 and E203K-SUR1. Login to comment 109 ABCC8 p.Glu203Lys The Q52E-Kir6.2//E203K-SUR1 channels exhibited a marked A SUR1 mutation functionally interacts with Q52E of Kir6.2 to enhance ATP sensitivity To identify a residue or residues in SUR1 that might interact with Q52E or Q52R to influence ATP sensitivity, we performed mutagenesis of SUR1, focusing on the following charged residues: K199, R202, E203, and K205. Login to comment 114 ABCC8 p.Glu203Lys These residues were mutated to oppositely charged amino acids Figure 2.ߓ Screening of SUR1 residues identifies the E203K mutation that when combined with Q52E in Kir6.2 gives rise to channels with extremely high ATP sensitivity. Login to comment 117 ABCC8 p.Glu203Lys ABCC8 p.Lys205Glu Only 1 mM ATP was tested in the cases of E203K-SUR1// Q52R-Kir6.2 and K205E-SUR1// Q52R-Kir6.2 because of extremely low ATP sensitivity. Login to comment 119 ABCC8 p.Glu203Lys (B) Representative traces from WT or Q52E-Kir6.2//E203K-SUR1 KATP channels exposed to various concentrations of ATP or nucleotide-free Kint/EDTA control solution; note difference in ATP concentrations used. Login to comment 121 ABCC8 p.Glu203Lys (C) Dose-response data illustrating the mean currents in several ATP concentrations relative to maximum in nucleotide-free solution for WT and Q52E-Kir6.2//E203K-SUR1 KATP channels. Login to comment 122 ABCC8 p.Glu203Lys Best fit curves were generated using the Hill equation (IC50: 11 &#b1; 1 &#b5;M for WT and 140 &#b1; 5 nM for Q52E-Kir6.2// E203K-SUR1). Login to comment 124 ABCC8 p.Glu203Lys For comparison, the best fit curve for Q52E-Kir6.2 (see Fig. 1) and mean currents for the three ATP concentrations tested on E203K-SUR1 channels (see A) were also included. Login to comment 125 ABCC8 p.Glu203Lys Error bars represent SEM, and some are smaller than the symbols. used to determine whether increased ATP sensitivity seen in the Q52E-Kir6.2//WT-SUR1 and Q52E-Kir6.2// E203K-SUR1 channels was related to decreased channel Po (Fig. 3). Login to comment 127 ABCC8 p.Glu203Lys ABCC8 p.Glu203Lys The fold increase of current from baseline was calculated (Fig. 3 B), with Q52E-Kir6.2//WT-SUR1 and Q52E-Kir6.2//E203K-SUR1 showing increased response com- paredwithWT(4.4&#b1;0.7,3.7&#b1;0.9vs.1.3&#b1;0.1,respectively, after second exposure), whereas the E203K-SUR1 response was less than WT (1.1 &#b1; 0.1). Login to comment 128 ABCC8 p.Glu203Lys Intrinsic Po was estimated using these values (PIP2 method) as well as via noise analysis; estimates from the two methods are compared in Fig. 3 C. Q52E-Kir6.2//WT-SUR1 and Q52E-Kir6.2//E203K-SUR1 mutant channels had significantly reduced Po compared with WT (0.28 &#b1; 0.05, 0.36 &#b1; 0.06 vs. 0.76 &#b1; 0.04 using the PIP2 method and 0.16 &#b1; 0.04, 0.31 &#b1; 0.04 vs. 0.76 &#b1; 0.03 using noise analysis, respectively). Login to comment 129 ABCC8 p.Glu203Lys Estimates of E203K Po are 0.92 &#b1; 0.02 and 0.83 &#b1; 0.02 using the PIP2 and noise analysis methods. Login to comment 130 ABCC8 p.Glu203Lys The analyses revealed that although there is a 10-fold difference in IC50 between Q52E-Kir6.2//WT-SUR1 and Q52E-Kir6.2// E203K-SUR1, their estimated intrinsic Po values are not significantly different. Login to comment 131 ABCC8 p.Glu203Lys This suggests that the unusually high ATP sensitivity of Q52E-Kir6.2//E203K-SUR1 can only be partially accounted for by changes in Po and/or channel-PIP2 interactions (see Discussion). Login to comment 133 ABCC8 p.Glu203Lys The result suggests that E203K of SUR1 interacts with Q52E of Kir6.2 either directly or indirectly to increase ATP sensitivity. Login to comment 138 ABCC8 p.Glu203Lys Both methods were Figure 3.ߓ Changes in intrinsic Po do not fully account for high Q52E-Kir6.2// E203K-SUR1 ATP sensitivity. Login to comment 146 ABCC8 p.Glu203Lys ABCC8 p.Glu203Lys Number in each dataset for PIP2 method is given in B (right); n for NA method is 19, 18, 17, and 19 for WT, E203K-SUR1, Q52E-Kir6.2, and Q52E-Kir6.2// E203K-SUR1, respectively. Login to comment 152 ABCC8 p.Glu203Cys These observations indicate that cross-linking between Q52C-Kir6.2 and E203C-SUR1 causes the channel to enter an ATP-independent closed state. Login to comment 153 ABCC8 p.Glu203Lys ABCC8 p.Glu203Cys Addition of H2O2 to channels already closed by 1 mM ATP also induced cross-linking as indicated by the greatly reduced channel activity after washout of H2O2 and ATP and subsequent increase in activity with Cross-linking between Q52C of Kir6.2 and E203C of SUR1 stabilizes channels in a closed state To test whether E203K of SUR1 and Q52E of Kir6.2 are in close proximity to interact directly, we substituted both residues with cysteines and performed cross-linking experiments. Login to comment 155 ABCC8 p.Glu203Cys In inside-out patches, Q52C-Kir6.2//E203C-SUR1 channels exhibited ATP sensitivity indistinguishable from that of WT channels (Fig. S3). Login to comment 158 ABCC8 p.Glu203Cys The residual currents could represent uncross-linked channels caused Figure 4.ߓ Reversible cysteine cross-linking is observed between Q52C-Kir6.2 and E203C-SUR1. Login to comment 159 ABCC8 p.Glu203Cys Representative traces of inside-out patch voltage-clamp recordings from COSm6 cell transfected with Q52C-Kir6.2 and E203C-SUR1. Login to comment 162 ABCC8 p.Glu203Cys (A) Current from Q52C-Kir6.2//E203C-SUR1 channels rapidly decreases to a plateau level in the presence of H2O2 and can be subsequently restored when DTT is applied. Login to comment 163 ABCC8 p.Glu203Cys This pattern of activity suggests that the proximity of Q52C-Kir6.2 and E203C-SUR1 is close enough to allow intersubunit disulfide bond formation. Login to comment 164 ABCC8 p.Glu203Cys (B) Cross-linking between Q52C-Kir6.2 and E203C-SUR1 can also occur from the ATP-bound, closed state as indicated by current decline with H2O2 in the presence of saturating ATP concentrations. Login to comment 166 ABCC8 p.Glu203Cys (C) Cross-linking between Q52C-Kir6.2 and E203C-SUR1 locks channels in a PIP2-insensitive closed state. Login to comment 173 ABCC8 p.Glu203Cys As shown in Fig. 4 C (and Fig. S4), PIP2 failed to recover the activity of cross-linked Q52C-Kir6.2//E203C-SUR1 channels; however, after exposure to DTT, channel activity was readily increased by PIP2. Login to comment 174 ABCC8 p.Glu203Cys These results indicate that cross-linking E203C of SUR1 with Q52C of Kir6.2 induces channel closure and stabilizes the channel in a closed state that cannot be activated by PIP2. Login to comment 177 ABCC8 p.Glu203Cys Occasionally we observed a decrease in current amplitude upon H2O2 exposure that differed from Q52C-Kir6.2//E203C-SUR1 channels in that it followed a much slower time course and was readily reversed upon returning to Kint/EDTA or exposure to PIP2 (Fig. 5 A, right). Login to comment 178 ABCC8 p.Glu203Cys Similar findings were made with WTKir6.2//E203C-SUR1 channels (n = 5 with three patches showing little effect by H2O2 and two patches showing decreased currents that were recovered by PIP2; Fig. 5 B). Login to comment 185 ABCC8 p.Glu203Lys ABCC8 p.Glu203Lys ABCC8 p.Glu203Cys The Q52K-Kir6.2 and E203-SUR1 (WT-SUR1) charge pair does not recapitulate the high ATP sensitivity observed in Q52E-Kir6.2//E203K-SUR1 channels Based on the high ATP sensitivity observed in the Q52E-Kir6.2//E203K-SUR1 channels and the evidence supporting physical proximity between the two residues, one Figure 5.ߓ Cross-linking does not occur in WT, WT-Kir6.2// E203C-SUR1, or Q52C-Kir6.2//WT-SUR1 channels. Login to comment 186 ABCC8 p.Glu203Cys (A-C) Representative traces of inside-out patch voltage-clamp recordings from COSm6 cell transfected with control WT (A), WT-Kir6.2// E203C-SUR1 (B), or Q52C-Kir6.2//WT-SUR1 (C) channels. Login to comment 190 ABCC8 p.Glu203Cys Occasional decreases in current were observed with H2O2 exposure, but always slower and less robust than compared with Q52C-Kir6.2// E203C-SUR1 channels (Fig. 4). Login to comment 198 ABCC8 p.Glu128Lys However, when coexpressed with E128K-SUR1, Q52R-Kir6.2 failed to confer increased channel interaction with PIP2. Login to comment 199 ABCC8 p.Glu128Lys ABCC8 p.Glu128Lys In fact, Q52R-Kir6.2//E128K-SUR1 channels were even more sensitive to neomycin than WT channels, consistent with reduced Po expected from the E128K-SUR1 mutation. Login to comment 200 ABCC8 p.Glu128Lys ABCC8 p.Glu203Lys As expected, addition of the E128K mutation in SUR1 also diminished the ability of Q52E-Kir6.2//E203K-SUR1 channels to respond to PIP2 stimulation (Fig. 7 B; also see Fig. 3 [A and B] for comparison). Login to comment 201 ABCC8 p.Glu128Lys Thus, the E128K mutation in SUR1 exerts a dominant effect over the Q52 mutations with regard to channel Po and PIP2 response. Login to comment 202 ABCC8 p.Glu128Lys Next, we measured ATP sensitivity of channels formed by coexpression of E128K-SUR1 and Q52R-Kir6.2. Login to comment 203 ABCC8 p.Glu128Lys ABCC8 p.Glu128Lys Rather than the very low ATP sensitivity seen in Q52R-Kir6.2//WT-SUR1 channels, Q52R-Kir6.2//E128K-SUR1 channels exhibited similar ATP sensitivity as WT-Kir6.2//E128K-SUR1 (Fig. 7, C and D). Login to comment 206 ABCC8 p.Glu128Cys ABCC8 p.Glu203Lys However, no change in channel activity was observed in Q52C-Kir6.2//E128C-SUR1 than WT (Fig. 6), in contrast to the near 100-fold increase in ATP sensitivity observed in Q52E-Kir6.2// E203K-SUR1 (Fig. 2). Login to comment 207 ABCC8 p.Glu203Lys These results suggest that the specific interaction between Q52E-Kir6.2 and E203K-SUR1 that results in a super ATP-sensitive channel is likely dependent on the structural context surrounding the mutant amino acid pair. Login to comment 208 ABCC8 p.Glu128Lys The effect of Q52-Kir6.2 mutation on ATP sensitivity is abrogated by a TMD0-SUR1 mutation E128K that uncouples SUR1 from Kir6.2 The profoundly reduced ATP sensitivity of the Q52R-Kir6.2//WT-SUR1 channel has been attributed to increased intrinsic channel open state stability (Proks et al., 2004). Login to comment 211 ABCC8 p.Glu128Lys A mutation in the TMD0 of SUR1, E128K, uncouples SUR1 from Kir6.2, resulting in reduced Po and diminished PIP2 response that resemble those seen in channels formed by Kir6.2&#e044;C alone (Pratt et al., 2009, 2011). Login to comment 212 ABCC8 p.Glu128Lys Interestingly, the WT-Kir6.2//E128K-SUR1 channels also have reduced ATP sensitivity close to that of Kir6.2&#e044;C channels, indicating that interactions between TMD0-SUR1 and Kir6.2 are required for full-length SUR1 to set the ATP sensitivity. Login to comment 213 ABCC8 p.Glu128Lys We therefore tested how the E128K-SUR1 mutation affects the ability of Q52R-Kir6.2 to increase channel Po and reduce ATP sensitivity. Login to comment 214 ABCC8 p.Glu128Lys ABCC8 p.Glu128Lys Note because the E128K mutation impairs channel trafficking to the cell surface (Yan et al., 2007), in all experiments involving the use of E128K-SUR1, we treated cells with 300 &#b5;M tolbutamide (a KATP channel chaperone which binds reversibly to the channel) overnight to rescue the trafficking defect and increase surface expression of the mutant channels as we have shown previously (Pratt et al., 2009, Figure 6.ߓ Q52K-Kir6.2//WT(E203)-SUR1 channels do not have extremely increased ATP sensitivity. Login to comment 221 ABCC8 p.Glu128Lys ABCC8 p.Glu128Lys ABCC8 p.Glu128Lys ABCC8 p.Glu203Lys ABCC8 p.Glu203Lys Error bars represent SEM, and some are smaller than the symbols. for Q52E-Kir6.2//E128K-SUR1 and Q52E-Kir6.2// E128K/E203K-SUR1 channels was closer to that of WT-Kir6.2//E128K-SUR1 (and Kir6.2&#e044;C channels [Pratt et al., 2009]) than that of either Q52E-Kir6.2//WT-SUR1 or Q52E-Kir6.2//E203K-SUR1 (Fig. 7, C and D). Login to comment 224 ABCC8 p.Glu128Lys ABCC8 p.Glu203Lys E128K-SUR1 also suppressed the effects of Q52E-Kir6.2 and Q52E-Kir6.2//E203K-SUR1 on ATP sensitivity. Login to comment 225 ABCC8 p.Glu128Lys Current inhibition by ATP Figure 7.ߓ Phenotype of mutations at Q52 of Kir6.2 and/or E203 of SUR1 is abrogated by the E128K mutation in SUR1. Login to comment 226 ABCC8 p.Glu128Lys (A) Q52R-Kir6.2 causes an increased apparent PIP2 affinity that is abrogated by E128K-SUR1. Login to comment 228 ABCC8 p.Glu128Lys The increase in apparent PIP2 affinity (i.e., right-shifted neomycin dose-response) of Q52R-Kir6.2 relative to WT is abolished by the inclusion of E128K-SUR1. Login to comment 229 ABCC8 p.Glu128Lys Dose-response curves (dotted lines) of currents inhibited by neomycin relative to control Kint/EDTA solution were calculated using the Hill equation (IC50 for WT, Q52R-Kir6.2, and Q52R-Kir6.2//E128K-SUR1 is 3.2 &#b1; 1.3 &#b5;M, 5,935 &#b1; 2,559 &#b5;M, and 0.9 &#b1; 0.5 &#b5;M, respectively). Login to comment 231 ABCC8 p.Glu128Lys ABCC8 p.Glu203Lys (B) E128K in SUR1 abolishes the ability of Q52E-Kir6.2//E203K-SUR1 channels to be stimulated by PIP2. Login to comment 235 ABCC8 p.Glu128Lys ABCC8 p.Glu203Lys (C and D) Inhibition by ATP was tested in channels composed of E128K-SUR1 with Q52E-Kir6.2, Q52R-Kir6.2, or Q52E-Kir6.2//E203K-SUR1. Login to comment 238 ABCC8 p.Glu128Lys (D) Averaged inhibition by 1, 0.1, and 0.01 mM ATP for various channel types with and without the E128K-SUR1 mutation. Login to comment 239 ABCC8 p.Glu128Lys For comparison, the degree of inhibition by 1 and 0.1 mM ATP for E128K-SUR1 is highlighted by gray dotted lines. Login to comment 243 ABCC8 p.Glu128Lys Despite this widely accepted view, the molecular mechanism underlying the effect of SUR1 E128K mutation precludes the molecular interactions between SUR1 and Kir6.2 necessary to define channel ATP sensitivity. Login to comment 244 ABCC8 p.Glu203Lys Channels formed by Q52E-Kir6.2 and E203K-SUR1 are not activated by metabolic inhibition ATP inhibition and MgADP stimulation are two primary physiological mechanisms that regulate KATP channel activity in &#e062; cells. Login to comment 248 ABCC8 p.Glu203Lys Because Q52E-Kir6.2//WT-SUR1 and Q52E-Kir6.2//E203K-SUR1 channels also show reduced intrinsic Po (Fig. 3 C), which could reduce efflux, we included the F55L-Kir6.2//WT-SUR1 mutant that exhibits &#e07a;10-fold reduced intrinsic Po but normal nucleotide sensitivities and surface expression for comparison (Lin et al., 2006b). Login to comment 250 ABCC8 p.Glu203Lys In contrast, both Q52E-Kir6.2//WT-SUR1 and Q52E-Kir6.2//E203K-SUR1 mutants had greatly reduced activity close to untransfected control cells (Fig. 8 C), despite surface expression levels similar to WT (Fig. 8, A and B). Login to comment 256 ABCC8 p.Glu203Lys A wealth of structure-function evidence supports the view that although the Kir6.2 tetramer harbors the ATP-binding sites for channel Figure 8.ߓ Increased ATP sensitivity in channels formed by E203K-SUR1 and Q52E-Kir6.2 compromise their ability to open in response to metabolic inhibition. Login to comment 260 ABCC8 p.Glu203Lys Mutations at Q52E-Kir6.2 and/or E203K-SUR1 do not disrupt protein trafficking. Login to comment 262 ABCC8 p.Glu203Lys Mutations at Q52E-Kir6.2 or E203K-SUR1 or both do not affect the number of channels at the cell surface. Login to comment 267 ABCC8 p.Glu203Lys Channels composed of Q52E-Kir6.2 with and without E203K-SUR1 show significantly diminished efflux compared with controls, WT and F55L-Kir6.2; the latter control was included because it has decreased intrinsic Po (&#e07a;0.11) but normal ATP sensitivity and surface expression. Login to comment 273 ABCC8 p.Glu203Lys Although Q52E-Kir6.2//E203K-SUR1 channels are highly sensitive to ATP inhibition, charge swap at the two positions as in Q52K-Kir6.2//WT(E203)-SUR1 channels does not recapitulate the same markedly increased ATP sensitivity. Login to comment 276 ABCC8 p.Glu203Lys Interestingly, the effect of Q52R-Kir6.2, Q52E-Kir6.2, or the combined Q52E-Kir6.2//E203K-SUR1 mutation on ATP sensitivity is dependent on another SUR1 residue, E128, in the short intracellular loop between transmembrane helices 3 and 4 of TMD0. Login to comment 278 ABCC8 p.Glu128Lys We recently showed that a naturally occurring mutation at this position, E128K, disrupts functional coupling between TMD0-SUR1 and Kir6.2, leading to channels that exhibit reduced Po and reduced PIP2 sensitivity as seen in channels formed by Kir6.2&#e044;C alone (Pratt et al., 2009, 2011). Login to comment 279 ABCC8 p.Glu128Lys In addition, E128K reduces channel ATP sensitivity to that seen in Kir6.2&#e044;C, suggesting the mutation not only prevents functional coupling between TMD0 and Kir6.2 with respect to Po but also between SUR1 structures downstream of TMD0 and Kir6.2 that control ATP sensitivity. Login to comment 280 ABCC8 p.Glu128Lys ABCC8 p.Glu128Lys ABCC8 p.Glu203Lys Our observations that when E128K-SUR1 was combined with Q52R-Kir6.2, Q52E-Kir6.2, or Q52E-Kir6.2//E203K-SUR1, the resulting channels all had PIP2 and ATP sensitivity closer to that of WT-Kir6.2//E128K-SUR1 (or Kir6.2&#e044;C) further support this notion. Login to comment 288 ABCC8 p.Glu203Lys First, to our knowledge, the Q52E-Kir6.2//E203K-SUR1 channel is the first mutant reported to have such a profound increase in ATP sensitivity. Login to comment 289 ABCC8 p.Glu203Cys Second, the Q52C-Kir6.2// E203C-SUR1 cross-linking results provide direct physical and functional evidence for a molecular interaction between SUR1 and Kir6.2 that controls channel activity. Login to comment 293 ABCC8 p.Glu203Lys We found the Po of Q52E-Kir6.2//E203K-SUR1 channels is indeed lower compared with WT channels (Fig. 3 C); however, decreased Po alone cannot account for the marked increase in ATP sensitivity of the channel because Q52E-Kir6.2//WT-SUR1 channels, despite having similarly reduced Po, are &#e07a;15-fold less sensitive to ATP inhibition. Login to comment 297 ABCC8 p.Glu203Lys Although it has been suggested that SUR1 increases channel sensitivity to ATP by participating in ATP binding (Babenko and Bryan, 2003; Babenko, 2005) direct evidence is lacking, and the single E203K mutation in SUR1 had little effect on channel ATP sensitivity. Login to comment 300 ABCC8 p.Glu203Cys That cross-linking of E203C-SUR1 and Q52C-Kir6.2 induces channel closure in the absence of ATP and renders channels refractory to PIP2 stimulation demonstrates that closure of the Kir6.2 pore complex can be achieved by simply altering molecular interactions between SUR1 and Kir6.2 without inhibitory ligands. Login to comment 301 ABCC8 p.Glu203Lys Together, the evidence led us to propose a scenario wherein the intersubunit interaction between E203K-SUR1 and Q52E-Kir6.2 allosterically stabilizes the channel complex in an ATP-bound closed state to increase the channel`s apparent ATP sensitivity. Login to comment 345 ABCC8 p.Glu203Lys In the Q52E-Kir6.2//E203K-SUR1 channels, the ATP sensitivity is so high it was impossible to find a concentration of MgATP or MgADP within the physiological range that would antagonize the inhibitory effect of the nucleotides. Login to comment