Structure and function of KATP channels - PROJECT SUMMARY ATP-sensitive potassium (KATP) channels, gated by intracellular nucleotides ATP and ADP, couple cell energetics with membrane excitability to govern a wide range of physiological processes vital to energy homeostasis. KATP channels are unique hetero-octameric membrane protein complexes of four inward rectifier K+ channel (Kir6.1 or Kir6.2) subunits and four sulfonylurea receptor (SUR1, SUR2A, or SUR2B) subunits. Various Kir6.x/SURx combinations generate KATP channel isoforms with distinct tissue distribution, nucleotide sensitivity, and pharmacology. The most prominent KATP channels are those of Kir6.2/SUR1, Kir6.2/SUR2A, and Kir6.1/SUR2B combinations, representing the major pancreatic, cardiac, and vascular smooth muscle isoforms, respectively. Mutations in genes encoding the various KATP channel proteins result in endocrine, cardiovascular, muscular and neuronal disorders, including congenital hyperinsulinism, neonatal diabetes, DEND syndrome, and Cantύ syndrome. The long-term goal of our research is to understand the structure-function relationship of KATP channel isoforms in health and disease and develop mechanism-based, isoform-specific therapies for disease caused by KATP channel dysfunction. A key barrier to progress has been a lack of detailed structural knowledge of the channels and their interactions with physiological and pharmacological ligands. In 2016, my lab broke this barrier by reporting the first high-resolution structure of the SUR1/Kir6.2 channel using single-particle cryo-electron microscopy (cryo-EM). We have since published a series of KATP channel structures bound to various ligands in different gated conformations at near atomic resolutions, which have significantly advanced our understanding of how the SUR and Kir6 subunits assemble and interact with each other and how they interact with ligands to control activity. Most exciting, we have begun to harness the structural knowledge to discover new compounds that modulate KATP channel assembly and gating. Despite the progress, significant knowledge gaps remain. In this new MIRA application, we seek to build on the tools and knowledge we have amassed and continue tackling the most pressing and challenging questions in the field using a multipronged approach that combines structural biology, computational biology, chemical biology, and electrophysiology. The three research directions we will focus on are: (1) solving additional cryoEM structures of pancreatic, cardiac, and vascular channels to obtain a comprehensive suite of channel structures in closed and open conformations, (2) elucidating the functional relevance of structural observations, especially focusing on lipid interactions and the role of intrinsically disordered regions, and (3) expanding KATP pharmacology by characterizing KATP structures bound to existing and novel drugs with a range of affinities and isoform-selectivity. By comparing and contrasting related KATP channel complexes we expect to uncover the general design principles that allow KATP channels to operate as ATP/ADP sensors and the specific mechanisms that underlie the unique gating properties and pharmacology of different KATP channel isoforms, which will have major and lasting positive impact on the KATP research field.
