NEM modification prevents high-affinity ATP binding to the first nucleotide binding fold of the sulphonylurea receptor, SUR1
Matsuo M., Tucker SJ., Ashcroft FM., Amachi T., Ueda K.
Pancreatic β-cell ATP-sensitive potassium channels, composed of SUR1 and Kir6.2 subunits, serve as a sensor for intracellular nucleotides and regulate glucose-induced insulin secretion. To learn more about the interaction of SUR1 with nucleotides, we examined the effect of N-ethylmaleimide (NEM) modification. Photoaffinity labeling of SUR1 with 5 μM 8-azido-[α-32P]ATP or 8-azido-[γ-32P]ATP was inhibited by NEM with K(i) of 1.8 μM and 2.4 μM, and Hill coefficients of 0.94 and 1.1, respectively. However, when the cysteine residue in the Walker A motif of the first nucleotide binding fold (NBF1) of SUR1 was replaced with serine (C717S), photoaffinity labeling was not inhibited by 100 μM NEM. These results suggest that NBF1 of SUR1 has a NEM-sensitive structure similar to that of NBF1 of MDR1, a multidrug transporter, and confirm NBF1 as the high-affinity ATP binding site on SUR1. Copyright (C) 1999 Federation of European Biochemical Societies.