Vascular K ATP channels comprising pore-forming Kir6.1 and regulatory SUR2B subunits regulate blood flow and blood pressure by modulating vascular tone. Variants with increased activity result in severe cardiovascular pathologies known as Cantú syndrome. Unique among K ATP isoforms, vascular K ATP channels lack spontaneous activity and require Mg-nucleotides for activation, but once activated, they are relatively insensitive to ATP inhibition. To gain insights into the structural basis of their nucleotide regulation, we determined cryo-EM structures of vascular K ATP channels in the presence of MgATP and MgADP. From a single cryo-EM sample we obtained distinct conformations of the fully assembled channel, including SUR2B in an MgADP-free nucleotide binding domain (NBD)-separated state, an MgADP-bound NBD-dimerized state, and a range of intermediate conformations defining the structural transition. These structures reveal the cryo-EM densities of intrinsically disordered regions (IDRs) of both Kir6.1 and SUR2B with functional implications. In the NBD-separated conformation, the Kir6.1-N terminus (KNt) is stabilized within the central cleft of SUR2B’s ABC-core. In contrast, in the NBD-dimerized conformation, KNt is excluded from the central cleft; instead, it is held by an ED domain consisting of 15 consecutive glutamate and aspartate residues within SUR2B’s N1-T2 linker which connects NBD1 (N1) with transmembrane domain 2 (T2). Notably, a regulatory helix in the N1-T2 linker is wedged between the two NBDs in the NBD-separated conformation, but upon NBD-dimerization, it moves outside the NBDs and interacts with the 42 C-terminal residues that are unique to SUR2B. All-atom molecular dynamics simulations of the full channel captured conformation-specific interactions between SUR2B’s N1-T2 linker, KNt, and the Kir6.1 C terminus. Our structures and the dynamic interplays observed between the IDRs suggest a crucial role of IDRs in MgADP/MgATP-dependent conformational switch in vascular K ATP channels.
Driggers et al. (Sun,) studied this question.