Vascular K-ATP channel structural dynamics reveal regulatory mechanism by Mg-nucleotides

Vascular tone is dependent on smooth muscle K-ATP channels comprising pore-forming Kir6.1 and regulatory SUR2B subunits, in which mutations cause Cantu syndrome. Unique among K-ATP isoforms, they lack spontaneous activity and require Mg-nucleotides for activation. Structural mechanisms underlying these properties are unknown. Here, we determined cryogenic electron microscopy structures of vascular K-ATP channels bound to inhibitory ATP and glibenclamide, which differ informatively from similarly determined pancreatic K-ATP channel isoform (Kir6.2/SUR1). Unlike SUR1, SUR2B subunits adopt distinct rotational "propeller" and "quatrefoil" geometries surrounding their Kir6.1 core. The glutamate/aspartate-rich linker connecting the two halves of the SUR-ABC core is observed in a quatrefoil-like conformation. Molecular dynamics simulations reveal MgADP-dependent dynamic tripartite interactions between this linker, SUR2B, and Kir6.1. The structures captured implicate a progression of intermediate states between MgADP-free inactivated, and MgADP-bound activated conformations wherein the glutamate/aspartate-rich linker participates as mobile autoinhibitory domain, suggesting a conformational pathway toward K-ATP channel activation.