Structural and Functional Characterization of a Human Potassium Channel, Kir2.1

Abstract

Inwardly rectifying potassium (Kir) channels are ubiquitously present in prokaryotic and eukaryotic cells. Kir channels selectively control the permeation of K+ ions in and out of the cell along the electrochemical gradient. Their inward rectification allows them to control the resting membrane potential and regulate many vital physiological functions such as heart rate, vascular tone, cell volume, and salt/fluid balance. Dysfunctions in Kir channels often lead to a multitude of diseases called “channelopathies”. Understanding the mechanisms involved in Kir channels and the effects of their mutations constitute a major challenge in the pharmaceutical and therapeutic research of the different channelopathies. In our case, we are interested in Andersen's syndrome, in which mutations of the human Kir2.1 protein are directly involved. By a biochemical, structural, and functional study, we aim to identify the differences between the wild type (WT) and two mutant channels in order to find links between the structure and the function of Kir2.1. This project aims at understanding the impact of clinically relevant disease-causing mutations on the structure and function of Kir2.1 potassium channels and to resolve the structure at high resolution using cryo-electron microscopy. The gating of Kir channels is modulated by various intracellular ligands that bind directly to the channel and enable its electrical activity. The lipid phosphatidylinositol-4,5-bisphosphate (PIP2) is essential to activate the eukaryotic Kir channels. We study a protein containing an arginine to histidine mutation in the putative PIP2 binding site and hypothesized that the loss of function observed in the mutated protein was due to a loss of interaction with PIP2. To test this hypothesis, we characterized the lipid-protein interaction using Surface Plasmon Resonance (SPR) and compared it with the WT protein. The SPR data shows that the mutant does not bind as well to the lipids as the WT.