Structure of an open K channel reveals tandem PIP binding sites mediating the Kir6.2 and SUR1 regulatory interface.

ATP-sensitive potassium (K ) channels, composed of four pore-lining Kir6.2 subunits and four regulatory sulfonylurea receptor 1 (SUR1) subunits, control insulin secretion in pancreatic β-cells. K channel opening is stimulated by PIP and inhibited by ATP. Mutations that increase channel opening by PIP reduce ATP inhibition and cause neonatal diabetes. Although considerable evidence has indicated PIP in K channel function, previously solved open-channel structures have lacked bound PIP , and mechanisms by which PIP regulates K channels remain unresolved. Here, we report the cryoEM structure of a K channel harboring the neonatal diabetes mutation Kir6.2-Q52R, bound to natural C18:0/C20:4 long-chain PIP in an open conformation. The structure reveals two adjacent PIP molecules between SUR1 and Kir6.2. The first PIP binding site is conserved among PIP -gated Kir channels. The second site forms uniquely in K at the interface of Kir6.2 and SUR1. Functional studies demonstrate both binding sites determine channel activity. Kir6.2 pore opening is associated with a twist of the Kir6.2 cytoplasmic domain and a rotation of the N-terminal transmembrane domain of SUR1, which widens the inhibitory ATP binding pocket to disfavor ATP binding. The open conformation is particularly stabilized by the Kir6.2-Q52R residue through cation-π bonding with SUR1-W51. Together, these results uncover the cooperation between SUR1 and Kir6.2 in PIP binding and gating, explain the antagonistic regulation of K channels by PIP and ATP, and provide the mechanism by which Kir6.2-Q52R stabilizes an open channel to cause neonatal diabetes.