Bienengraeber M, Alekseev A E, Abraham M R, Carrasco A J, Moreau C, Vivaudou M, Dzeja P P, Terzic A
*Division of Cardiovascular Diseases, Departments of Medicine, Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, Minnesota 55905, USA.
FASEB J. 2000 Oct;14(13):1943-52. doi: 10.1096/fj.00-0027com.
ATP-sensitive K+ (KATP) channels are unique metabolic sensors formed by association of Kir6.2, an inwardly rectifying K+ channel, and the sulfonylurea receptor SUR, an ATP binding cassette protein. We identified an ATPase activity in immunoprecipitates of cardiac KATP channels and in purified fusion proteins containing nucleotide binding domains NBD1 and NBD2 of the cardiac SUR2A isoform. NBD2 hydrolyzed ATP with a twofold higher rate compared to NBD1. The ATPase required Mg2+ and was insensitive to ouabain, oligomycin, thapsigargin, or levamisole. K1348A and D1469N mutations in NBD2 reduced ATPase activity and produced channels with increased sensitivity to ATP. KATP channel openers, which bind to SUR, promoted ATPase activity in purified sarcolemma. At higher concentrations, openers reduced ATPase activity, possibly through stabilization of MgADP at the channel site. K1348A and D1469N mutations attenuated the effect of openers on KATP channel activity. Opener-induced channel activation was also inhibited by the creatine kinase/creatine phosphate system that removes ADP from the channel complex. Thus, the KATP channel complex functions not only as a K+ conductance, but also as an enzyme regulating nucleotide-dependent channel gating through an intrinsic ATPase activity of the SUR subunit. Modulation of the channel ATPase activity and/or scavenging the product of the ATPase reaction provide novel means to regulate cellular functions associated with KATP channel opening.
ATP敏感性钾离子（KATP）通道是一种独特的代谢传感器，由内向整流钾离子通道Kir6.2和磺脲类受体SUR（一种ATP结合盒蛋白）结合形成。我们在心脏KATP通道的免疫沉淀物以及含有心脏SUR2A亚型核苷酸结合结构域NBD1和NBD2的纯化融合蛋白中鉴定出一种ATP酶活性。与NBD1相比，NBD2水解ATP的速率高出两倍。该ATP酶需要Mg2+，且对哇巴因、寡霉素、毒胡萝卜素或左旋咪唑不敏感。NBD2中的K1348A和D1469N突变降低了ATP酶活性，并产生了对ATP敏感性增加的通道。与SUR结合的KATP通道开放剂可促进纯化肌膜中的ATP酶活性。在较高浓度下，开放剂会降低ATP酶活性，可能是通过在通道位点稳定MgADP来实现的。K1348A和D1469N突变减弱了开放剂对KATP通道活性的影响。开放剂诱导的通道激活也受到肌酸激酶/磷酸肌酸系统的抑制，该系统可从通道复合物中去除ADP。因此，KATP通道复合物不仅作为钾离子电导发挥作用，还作为一种酶，通过SUR亚基的内在ATP酶活性调节核苷酸依赖性通道门控。调节通道ATP酶活性和/或清除ATP酶反应产物为调节与KATP通道开放相关的细胞功能提供了新方法。
