E224G Regulation of the PIP$_{2}$-Induced Gating Kinetics of Kir2.1 Channels
Shu-Xi Ren1, Jun-Wei Li1, Su-Hua Zhang1, D. E. Logothetis2, Hai-Long An1**, Yong Zhan1**
1Key Laboratory of Molecular Biophysics of Hebei Province, Institute of Biophysics, School of Sciences, Hebei University of Technology, Tianjin 300401 2Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Virginia, USA
Abstract：As a member of the inwardly rectifying K$^{+}$ channel (Kir) family, Kir2.1 allows K$^{+}$ to influx the cell more easily than to efflux, a biophysical phenomenon named inward rectification. The function of Kir2.1 is to set the resting membrane potential and modulate membrane excitability. It has been reported that residue E224 plays a key role in regulating inward rectification. The mutant Kir2.1 (E224G) displays weaker inward rectification than the WT channel. Gating of Kir2.1 depends on the membrane lipid, PIP$_{2}$, such that the channel gates are closed in the absence of PIP$_{2}$. Here we perform electrophysiological and computational approaches, and demonstrate that E224 also plays an important role in the PIP$_{2}$-dependent activation of Kir2.1 in addition to its influence on inward rectification. The E224G mutant takes 4.5 times longer to be activated by PIP$_{2}$. To probe the mechanism by which E224G slows the channel opening kinetics, we perform targeted molecular dynamics simulations and find that the mutant weakens the interactions between CD-loop and C-linker (H221-R189) and the adjacent G-loops (R312-E303) which are thought to stabilize the open state of the channel in our previous work. These data provide new insights into the regulation of Kir2.1 channel activity and suggest that a common mechanism may be involved in the distinct biophysical processes, such as inward rectification and PIP$_{2}$-induced gating.
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2017, Vol. 34 
