Structural Biology

Biography

Biography: Irena Levitan

Abstract

Cholesterol is known to play a major role in regulating the function of multiple membrane proteins including a growing number of ion channels. Our studies focus on inwardly-rectifying K+ (Kir) channels that are ubiquitously expressed in mammalian cells and are known to play major role in membrane excitability and shear stress sensation. In this study, we have shown that Kir channels are suppressed by loading the cells with cholesterol and enhanced by cholesterol depletion. A series of studies revealed that cholesterol interacts with the channels directly by stabilizing them in a long-lived closed “silent” state and that multiple structural features of the channels are essential for conferring their cholesterol sensitivity. Using a combined computational-experimental approach, we show that cholesterol may bind to two nonannular regions that form hydrophobic pockets between the transmembrane helices of the adjacent subunits of the channel. The location of the binding regions suggests that, cholesterol modulates channel function by affecting the hinging motion at the center of the porelining transmembrane helix that underlies channel gating. In addition, we identified a series of residues in the C and N-terminus of the channel. These are critical for conferring cholesterol sensitivity to the channels, but are not part of the binding sites. These residues form a distinct cytosolic structure, a cholesterol sensitivity belt which surrounds the cytosolic pore of the channel in proximity to the transmembrane (TM) domain, and includes residues whose mutation results in abrogation of the channel’s cholesterol sensitivity. Further analysis identified a reversal residue chain comprised of residues that link one of the cholesterol sensitivity belt residues with a distant cytosolic residue that constitute a two-way molecular switch of the channel sensitivity to cholesterol. Further studies are needed to elucidate the connection between cholesterol binding and channel. 

References:

1. Rosenhouse-Dantsker A, Noskov S, Durdagi S, Logothetis DE, Levitan I. Identification of novel cholesterol-binding regions in Kir2 channels. JBC, 288(43):31154-64, 2013
2. Han H., Rosenhouse-Dantsker A. Gnanasambandam R. Epshtein Y. Chen Z., Sachs F, Minshall RD and I Levitan. Silencing of Kir2 channels by caveolin-1: cross-talk with cholesterol. Journal of Physiology, 592:4025-38, 2014
3. Rosenhouse-Dantsker A. Epshtein Y. and I. Levitan. Interplay between lipid modulators of Kir2 channels: cholesterol and PIP2.  Computational and Structural Biotech Journal, 11(19):131-7, 2014
4. Bukiya AN, Osborn CV, Kuntamallappanavar G, Toth PT, Baki L, Kowalsky GB, Oh MO, Dopico AM, Levitan I. and A. Rosenhouse-Dantsker. Cholesterol increases the open probability of cardiac KACh currents, BBA Membranes, 848:2406-13, 2015
5. Ahn SJ, Fancher IS, Bian JT, Zhang CX, Schwab S, Gaffin R, Phillips SA, and I Levitan. Inwardly-rectifying K+ channels are major contributors to flow-induced vasodilation in resistance arteries. J of Physiology. In Press.