Fig. 2.

L213R markedly elevates on-cell P_O, does not affect the unitary conductance, and slightly decreases functional expression of (SUR1/K_IR6.2)₄ complexes without altering their labeling with 1 nM ¹²⁵I-azidoglibenclamide. Inset shows similar affinity photolabeling of immature, core-glycosylated SUR1_L213R vs SUR1 with the second generation SU, and modestly reduced amount of mature, complex-glycosylated mutants trafficking with colabeled K_IR6.2. As was reported earlier, nanomolar glibenclamide or micromolar tolbutamide abolish labelling by displacing the photoreactive analogue of glibenclamide which does not label K_IR6.2 expressed without SUR1 [17,18,26], the L0 loop apparently coordinates the photoreactive group-containing non-sulfonylurea moiety of the drug [22,27], and deleting the N-terminus of K_IR6.2 eliminates its colabeling without disrupting KATP assembly [18] required for trafficking of either SUR1 or glycosylation site-free K_IR6.2 to the plasma membrane [26,28]. Therefore, normal affinity labeling of SUR1_L213R and K_IR6.2, while slightly reduced amount of mature SUR1_L213R, suggest that the mutation does not alter the SU binding site or the direct proximity of L0 to the K_IR N-terminal helix, while slightly reducing KATP trafficking to the plasma membrane; n ≥ 5 for each bar.