Journal Article

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

Patton, Bruce L., Yang, Zhongying, Zuckerman, Daniel M., Russo, John D., Shyng, Show-Ling, Sung, Min Woo, Mostofian, Barmak, Driggers, Camden M.

2021

Overview

Vascular K ATP channels formed by the potassium channel Kir6.1 and its regulatory protein SUR2B maintain blood pressure in the physiological range. Overactivity of the channel due to genetic mutations in either Kir6.1 or SUR2B causes severe cardiovascular pathologies known as Cantú syndrome. The cryogenic electron microscopy structures of the vascular K ATP channel reported here show multiple, dynamically related conformations of the regulatory subunit SUR2B. Molecular dynamics simulations reveal the negatively charged ED-domain in SUR2B, a stretch of 15 glutamate (E) and aspartate (D) residues not previously resolved, play a key MgADP-dependent role in mediating interactions at the interface between the SUR2B and Kir6.1 subunits. Our findings provide a mechanistic understanding of how channel activity is regulated by intracellular MgADP. Vascular tone is dependent on smooth muscle K ATP channels comprising pore-forming Kir6.1 and regulatory SUR2B subunits, in which mutations cause Cantú 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.

• Subject: Adenosine Diphosphate - metabolism / Adenosine Triphosphate - metabolism / Cardiomegaly - metabolism / Humans / Hypertrichosis - metabolism / KATP Channels - genetics / KATP Channels - metabolism / KATP Channels - ultrastructure / Muscle, Smooth - metabolism / Osteochondrodysplasias - metabolism / Pancreas - metabolism / Potassium Channels - metabolism / Potassium Channels, Inwardly Rectifying - metabolism / Structure-Activity Relationship / Sulfonylurea Receptors - genetics / Sulfonylurea Receptors - metabolism / Sulfonylurea Receptors - ultrastructure