Bimodal regulation of an Elk subfamily K+ channel by phosphatidylinositol 4,5-bisphosphate.
Phosphatidylinositol 4,5-bisphosphate (PIP2) regulates Shaker K+ channels and voltage-gated Ca2+ channels in a bimodal fashion by inhibiting voltage activation while stabilizing open channels. Bimodal regulation is conserved in hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, but voltage activation is enhanced while the open channel state is destabilized. The proposed sites of PIP2 regulation in these channels include the voltage-sensor domain (VSD) and conserved regions of the proximal cytoplasmic C terminus. Relatively little is known about PIP2 regulation of Ether-á-go-go (EAG) channels, a metazoan-specific family of K+ channels that includes three gene subfamilies, Eag (Kv10), Erg (Kv11), and Elk (Kv12). We examined PIP2 regulation of the Elk subfamily potassium channel human Elk1 to determine whether bimodal regulation is conserved within the EAG K+ channel family. Open-state stabilization by PIP2 has been observed in human Erg1, but the proposed site of regulation in the distal C terminus is not conserved among EAG family channels. We show that PIP2 strongly inhibits voltage activation of Elk1 but also stabilizes the open state. This stabilization produces slow deactivation and a mode shift in voltage gating after activation. However, removal of PIP2 has the net effect of enhancing Elk1 activation. R347 in the linker between the VSD and pore (S4-S5 linker) and R479 near the S6 activation gate are required for PIP2 to inhibit voltage activation. The ability of PIP2 to stabilize the open state also requires these residues, suggesting an overlap in sites central to the opposing effects of PIP2 on channel gating. Open-state stabilization in Elk1 requires the N-terminal eag domain (PAS domain + Cap), and PIP2-dependent stabilization is enhanced by a conserved basic residue (K5) in the Cap. Our data shows that PIP2 can bimodally regulate voltage gating in EAG family channels, as has been proposed for Shaker and HCN channels. PIP2 regulation appears fundamentally different for Elk and KCNQ channels, suggesting that, although both channel types can regulate action potential threshold in neurons, they are not functionally redundant.
Department of Biology and Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802 Department of Biology and Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802.
Xiaofan
X
Li
Department of Biology, University of Maryland, College Park, MD 20742.
Andriy
A
Anishkin
Department of Biology and Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802.
Hansi
H
Liu
Department of Biology and Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802 Department of Biology and Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802.
Damian B
DB
van Rossum
Arkansas Children's Nutrition Center and Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, AR 72202 Arkansas Children's Nutrition Center and Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, AR 72202.
Sree V
SV
Chintapalli
Department of Biology and Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802.
Jessica K
JK
Sassic
Department of Biology and Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802.
David
D
Gallegos
Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195.
Kendra
K
Pivaroff-Ward
Department of Biology and Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802 Department of Biology and Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802 tjj3@psu.edu.
Timothy
T
Jegla
D000595:Amino Acid Sequence; D006801:Humans; D015640:Ion Channel Gating; D008969:Molecular Sequence Data; D009865:Oocytes; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D050807:ets-Domain Protein Elk-1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
C494112:ELK1 protein, human; D019269:Phosphatidylinositol 4,5-Diphosphate; D050807:ets-Domain Protein Elk-1