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Salt bridges and gating in the COOH-terminal region of HCN2 and CNGA1 channels.
J Gen Physiol. 2004 Dec; 124(6):663-77.JG

Abstract

Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels and cyclic nucleotide-gated (CNG) channels are activated by the direct binding of cyclic nucleotides. The intracellular COOH-terminal regions exhibit high sequence similarity in all HCN and CNG channels. This region contains the cyclic nucleotide-binding domain (CNBD) and the C-linker region, which connects the CNBD to the pore. Recently, the structure of the HCN2 COOH-terminal region was solved and shown to contain intersubunit interactions between C-linker regions. To explore the role of these intersubunit interactions in intact channels, we studied two salt bridges in the C-linker region: an intersubunit interaction between C-linkers of neighboring subunits, and an intrasubunit interaction between the C-linker and its CNBD. We show that breaking these salt bridges in both HCN2 and CNGA1 channels through mutation causes an increase in the favorability of channel opening. The wild-type behavior of both HCN2 and CNGA1 channels is rescued by switching the position of the positive and negative residues, thus restoring the salt bridges. These results suggest that the salt bridges seen in the HCN2 COOH-terminal crystal structure are also present in the intact HCN2 channel. Furthermore, the similar effects of the mutations on HCN2 and CNGA1 channels suggest that these salt bridge interactions are also present in the intact CNGA1 channel. As disrupting the interactions leads to channels with more favorable opening transitions, the salt bridges appear to stabilize a closed conformation in both the HCN2 and CNGA1 channels. These results suggest that the HCN2 COOH-terminal crystal structure contains the C-linker regions in the resting configuration even though the CNBD is ligand bound, and channel opening involves a rearrangement of the C-linkers and, thus, disruption of the salt bridges. Discovering that one portion of the COOH terminus, the CNBD, can be in the activated configuration while the other portion, the C-linker, is not activated has lead us to suggest a novel modular gating scheme for HCN and CNG channels.

Authors+Show Affiliations

Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA.No affiliation info available

Pub Type(s)

Journal Article
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

15572346

Citation

Craven, Kimberley B., and William N. Zagotta. "Salt Bridges and Gating in the COOH-terminal Region of HCN2 and CNGA1 Channels." The Journal of General Physiology, vol. 124, no. 6, 2004, pp. 663-77.
Craven KB, Zagotta WN. Salt bridges and gating in the COOH-terminal region of HCN2 and CNGA1 channels. J Gen Physiol. 2004;124(6):663-77.
Craven, K. B., & Zagotta, W. N. (2004). Salt bridges and gating in the COOH-terminal region of HCN2 and CNGA1 channels. The Journal of General Physiology, 124(6), 663-77.
Craven KB, Zagotta WN. Salt Bridges and Gating in the COOH-terminal Region of HCN2 and CNGA1 Channels. J Gen Physiol. 2004;124(6):663-77. PubMed PMID: 15572346.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Salt bridges and gating in the COOH-terminal region of HCN2 and CNGA1 channels. AU - Craven,Kimberley B, AU - Zagotta,William N, PY - 2004/12/2/pubmed PY - 2005/6/14/medline PY - 2004/12/2/entrez SP - 663 EP - 77 JF - The Journal of general physiology JO - J Gen Physiol VL - 124 IS - 6 N2 - Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels and cyclic nucleotide-gated (CNG) channels are activated by the direct binding of cyclic nucleotides. The intracellular COOH-terminal regions exhibit high sequence similarity in all HCN and CNG channels. This region contains the cyclic nucleotide-binding domain (CNBD) and the C-linker region, which connects the CNBD to the pore. Recently, the structure of the HCN2 COOH-terminal region was solved and shown to contain intersubunit interactions between C-linker regions. To explore the role of these intersubunit interactions in intact channels, we studied two salt bridges in the C-linker region: an intersubunit interaction between C-linkers of neighboring subunits, and an intrasubunit interaction between the C-linker and its CNBD. We show that breaking these salt bridges in both HCN2 and CNGA1 channels through mutation causes an increase in the favorability of channel opening. The wild-type behavior of both HCN2 and CNGA1 channels is rescued by switching the position of the positive and negative residues, thus restoring the salt bridges. These results suggest that the salt bridges seen in the HCN2 COOH-terminal crystal structure are also present in the intact HCN2 channel. Furthermore, the similar effects of the mutations on HCN2 and CNGA1 channels suggest that these salt bridge interactions are also present in the intact CNGA1 channel. As disrupting the interactions leads to channels with more favorable opening transitions, the salt bridges appear to stabilize a closed conformation in both the HCN2 and CNGA1 channels. These results suggest that the HCN2 COOH-terminal crystal structure contains the C-linker regions in the resting configuration even though the CNBD is ligand bound, and channel opening involves a rearrangement of the C-linkers and, thus, disruption of the salt bridges. Discovering that one portion of the COOH terminus, the CNBD, can be in the activated configuration while the other portion, the C-linker, is not activated has lead us to suggest a novel modular gating scheme for HCN and CNG channels. SN - 0022-1295 UR - https://www.unboundmedicine.com/medline/citation/15572346/Salt_bridges_and_gating_in_the_COOH_terminal_region_of_HCN2_and_CNGA1_channels_ DB - PRIME DP - Unbound Medicine ER -