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cAMP binds to closed, inactivated, and open sea urchin HCN channels in a state-dependent manner
Hyperpolarization-activated cyclic-nucleotide–modulated (HCN) channels are nonselective cation channels that regulate electrical activity in the heart and brain. Previous studies of mouse HCN2 (mHCN2) channels have shown that cAMP binds preferentially to and stabilizes these channels in the open sta...
Autores principales: | , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
Rockefeller University Press
2019
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6363418/ https://www.ncbi.nlm.nih.gov/pubmed/30541772 http://dx.doi.org/10.1085/jgp.201812019 |
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author | Idikuda, Vinay Gao, Weihua Su, Zhuocheng Liu, Qinglian Zhou, Lei |
author_facet | Idikuda, Vinay Gao, Weihua Su, Zhuocheng Liu, Qinglian Zhou, Lei |
author_sort | Idikuda, Vinay |
collection | PubMed |
description | Hyperpolarization-activated cyclic-nucleotide–modulated (HCN) channels are nonselective cation channels that regulate electrical activity in the heart and brain. Previous studies of mouse HCN2 (mHCN2) channels have shown that cAMP binds preferentially to and stabilizes these channels in the open state—a simple but elegant implementation of ligand-dependent gating. Distinct from mammalian isoforms, the sea urchin (spHCN) channel exhibits strong voltage-dependent inactivation in the absence of cAMP. Here, using fluorescently labeled cAMP molecules as a marker for cAMP binding, we report that the inactivated spHCN channel displays reduced cAMP binding compared with the closed channel. The reduction in cAMP binding is a voltage-dependent process but proceeds at a much slower rate than the movement of the voltage sensor. A single point mutation in the last transmembrane domain near the channel’s gate, F459L, abolishes inactivation and concurrently reverses the response to hyperpolarizing voltage steps from a decrease to an increase in cAMP binding. ZD7288, an open channel blocker that interacts with a region close to the activation/inactivation gate, dampens the reduction of cAMP binding to inactivated spHCN channels. In addition, compared with closed and “locked” closed channels, increased cAMP binding is observed in channels purposely locked in the open state upon hyperpolarization. Thus, the order of cAMP-binding affinity, measured by the fluorescence signal from labeled cAMP, ranges from high in the open state to intermediate in the closed state to low in the inactivated state. Our work on spHCN channels demonstrates intricate state-dependent communications between the gate and ligand-binding domain and provides new mechanistic insight into channel inactivation/desensitization. |
format | Online Article Text |
id | pubmed-6363418 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2019 |
publisher | Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-63634182019-08-04 cAMP binds to closed, inactivated, and open sea urchin HCN channels in a state-dependent manner Idikuda, Vinay Gao, Weihua Su, Zhuocheng Liu, Qinglian Zhou, Lei J Gen Physiol Research Articles Hyperpolarization-activated cyclic-nucleotide–modulated (HCN) channels are nonselective cation channels that regulate electrical activity in the heart and brain. Previous studies of mouse HCN2 (mHCN2) channels have shown that cAMP binds preferentially to and stabilizes these channels in the open state—a simple but elegant implementation of ligand-dependent gating. Distinct from mammalian isoforms, the sea urchin (spHCN) channel exhibits strong voltage-dependent inactivation in the absence of cAMP. Here, using fluorescently labeled cAMP molecules as a marker for cAMP binding, we report that the inactivated spHCN channel displays reduced cAMP binding compared with the closed channel. The reduction in cAMP binding is a voltage-dependent process but proceeds at a much slower rate than the movement of the voltage sensor. A single point mutation in the last transmembrane domain near the channel’s gate, F459L, abolishes inactivation and concurrently reverses the response to hyperpolarizing voltage steps from a decrease to an increase in cAMP binding. ZD7288, an open channel blocker that interacts with a region close to the activation/inactivation gate, dampens the reduction of cAMP binding to inactivated spHCN channels. In addition, compared with closed and “locked” closed channels, increased cAMP binding is observed in channels purposely locked in the open state upon hyperpolarization. Thus, the order of cAMP-binding affinity, measured by the fluorescence signal from labeled cAMP, ranges from high in the open state to intermediate in the closed state to low in the inactivated state. Our work on spHCN channels demonstrates intricate state-dependent communications between the gate and ligand-binding domain and provides new mechanistic insight into channel inactivation/desensitization. Rockefeller University Press 2019-02-04 /pmc/articles/PMC6363418/ /pubmed/30541772 http://dx.doi.org/10.1085/jgp.201812019 Text en © 2019 Idikuda et al. http://www.rupress.org/terms/https://creativecommons.org/licenses/by-nc-sa/4.0/This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms/). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/). |
spellingShingle | Research Articles Idikuda, Vinay Gao, Weihua Su, Zhuocheng Liu, Qinglian Zhou, Lei cAMP binds to closed, inactivated, and open sea urchin HCN channels in a state-dependent manner |
title | cAMP binds to closed, inactivated, and open sea urchin HCN channels in a state-dependent manner |
title_full | cAMP binds to closed, inactivated, and open sea urchin HCN channels in a state-dependent manner |
title_fullStr | cAMP binds to closed, inactivated, and open sea urchin HCN channels in a state-dependent manner |
title_full_unstemmed | cAMP binds to closed, inactivated, and open sea urchin HCN channels in a state-dependent manner |
title_short | cAMP binds to closed, inactivated, and open sea urchin HCN channels in a state-dependent manner |
title_sort | camp binds to closed, inactivated, and open sea urchin hcn channels in a state-dependent manner |
topic | Research Articles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6363418/ https://www.ncbi.nlm.nih.gov/pubmed/30541772 http://dx.doi.org/10.1085/jgp.201812019 |
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