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Cytoplasmic Autoinhibition in HCN Channels is Regulated by the Transmembrane Region.

Authors
  • Page, Dana A1
  • Magee, Kaylee E A1, 2
  • Li, Jessica1
  • Jung, Matthew1
  • Young, Edgar C3
  • 1 Department of Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada. , (Canada)
  • 2 Department of Biology, Kwantlen Polytechnic University, 12666 72 Avenue, Surrey, BC, V3W 2M8, Canada. , (Canada)
  • 3 Department of Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada. [email protected] , (Canada)
Type
Published Article
Journal
The Journal of Membrane Biology
Publisher
Springer-Verlag
Publication Date
Apr 01, 2020
Volume
253
Issue
2
Pages
153–166
Identifiers
DOI: 10.1007/s00232-020-00111-8
PMID: 32146488
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Hyperpolarization-activated cation-nonselective (HCN) channels regulate electrical activity in the brain and heart in a cAMP-dependent manner. The voltage-gating of these channels is mediated by a transmembrane (TM) region but is additionally regulated by direct binding of cAMP to a cyclic nucleotide-binding (CNB) fold in the cytoplasmic C-terminal region. Cyclic AMP potentiation has been explained by an autoinhibition model which views the unliganded CNB fold as an inhibitory module whose influence is disrupted by cAMP binding. However, the HCN2 subtype uses two other CNB fold-mediated mechanisms called open-state trapping and Quick-Activation to respectively slow the deactivation kinetics and speed the activation kinetics, against predictions of an autoinhibition model. To test how these multiple mechanisms are influenced by the TM region, we replaced the TM region of HCN2 with that of HCN4. This HCN4 TM-replacement preserved cAMP potentiation but augmented the magnitude of autoinhibition by the unliganded CNB fold; it moreover disrupted open-state trapping and Quick-Activation so that autoinhibition became the dominant mechanism contributed by the C-terminal region to determine kinetics. Truncation within the CNB fold partially relieved this augmented autoinhibition. This argues against the C-terminal region acting like a portable module with consistent effects on TM regions of different subtypes. Our findings provide evidence that functional interactions between the HCN2 TM region and C-terminal region govern multiple CNB fold-mediated mechanisms, implying that the molecular mechanisms of autoinhibition, open-state trapping, and Quick-Activation include participation of TM region structures.

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