Adenine Nucleotides Regulate Syntaxin 1A Binding to the Sulfonylurea Receptor 1 (SUR1)
Abstract Number: 1642-P
Authors: YOUHOU KANG, HUANLI XIE, HERBERT Y. GAISANO
Institutions: Toronto, ON, Canada
Results: Islet β-cell ATP sensitive potassium (KATP) channel consists of pore-forming Kir6.2 and regulatory SUR1 subunits. We recently reported (J. Biol. Chem. in press) that SNARE protein Syntaxin-1A (Syn-1A) bound to SUR1 at both nucleotide binding folds (NBF-1 and C-terminal NBF-2). At low ATP concentration, Syn-1A was able to inhibit KATP channels in both freshly isolated-islet β-cells and cultured insulinoma cells. The Syn-1A inhibition was mediated via NBF-1 and could be blocked by ADP. This led us to postulate that ATP and ADP could influence Syn-1A interactions with the NBFs of SUR1. In fact, we now demonstrate that ATP inhibited the binding of Syn-1A to both NBF-1 and NBF-2 of SUR1 in a dose-dependent manner, with ED50 of 3.1 mM and 3.9 mM, respectively. Addition of 2 mM Mg2+ shifted the dose-response curve to left. Surprisingly, ADP (IC50 at 3.4 mM and 4.7 mM, respectively) and AMP also decreased the binding of Syn-1A to both NBFs. These results suggest that ATP and ADP might be undergoing hydrolysis to AMP as to exhibit a similar effect. However, ATP-γ-S, a non-hydrolysable ATP analogue, and ADP-β-S, a non-hydrolysable ADP analogue, could mimic the ATP and ADP effects, respectively. In the presence of 5 mM ATP, vanadate, an ATPase inhibitor, was not able to prevent ATP from inhibition of Syn-1A binding to both NBFs. When ATP and ADP were mixed to simulate physiologic changes in ATP/ADP ratio, the binding of Syn-1A to NBFs still decreased with increasing ATP concentration in the presence of 1, 2, or 3 mM ADP. We conclude that (1) Syn-1A binding to both NBFs of SUR1 is regulated by ATP, ADP and AMP, suggesting the adenine ring in these nucleotides may be the putative domain; (2) ATP and ADP hydrolysis is not needed for these effects; (3) Mg2+ facilitates the Syn-1A binding to NBFs of SUR-1.