Reinterpreting the Action of ATP Analogs on KATP Channels

摘要: Neuroendocrine-type KATP channels, (SUR1/Kir6.2)4, couple the transmembrane flux of K+, and thus membrane potential, with cellular metabolism in various cell types including insulin-secreting β-cells. Mutant channels reduced activity are a cause congenital hyperinsulinism, whereas hyperactive neonatal diabetes. A current regulatory model proposes that ATP hydrolysis is required to switch SUR1 into post-hydrolytic conformations able antagonize inhibitory action nucleotide binding at Kir6.2 pore, coupling enzymatic channel activities. Alterations ATPase proposed contribute diabetes type 2 risk. The partly based on ability analogs such as adenosine 5′-(β,γ-imino)triphosphate (AMP-PNP) 5′-O-(thiotriphosphate) (ATPγS) stimulate activity, presumably by reducing hydrolysis. This study uses substitution catalytic glutamate, SUR1E1507Q, significantly increased affinity for ATP, probe these conformational switching. ATPγS, slowly hydrolyzable analog, switches conformations, albeit affinity. Nonhydrolyzable AMP-PNP 5′-(β,γ-methylenetriphosphate) (AMP-PCP) alone fail SUR1, but do reverse ATP-induced AMP-PCP displaces 8-azido-[32P]ATP from noncanonical NBD1 SUR1. consistent structural data an asymmetric bacterial ABC protein shows binds selectively NBD prevent results imply MgAMP-PNP MgAMP-PCP (AMP-PxP) activate because they not support dimerization switching, rather than limiting activity.