@article{99565730f3f148dabed07491b5fbdfe9,
title = "Helix breaking transition in the S4 of HCN channel is critical for hyperpolarization-dependent gating",
abstract = "In contrast to most voltage-gated ion channels, hyperpolarization- and cAMP gated (HCN) ion channels open on hyperpolarization. Structure-function studies show that the voltage-sensor of HCN channels are unique but the mechanisms that determine gating polarity remain poorly understood. All atom molecular dynamics simulations (\textasciitilde{}20 µs) of HCN1 channel under hyperpolarization reveals an initial downward movement of the S4 voltage-sensor but following the transfer of last gating charge, the S4 breaks into two sub-helices with the lower sub-helix becoming parallel to the membrane. Functional studies on bipolar channels show that the gating polarity strongly correlates with helical turn propensity of the substituents at the breakpoint. Remarkably, in a proto-HCN background, the replacement of breakpoint serine with a bulky hydrophobic amino acid is sufficient to completely flip the gating polarity from inward to outward-rectifying. Our studies reveal an unexpected mechanism of inward rectification involving a linker sub-helix emerging from HCN S4 during hyperpolarization.",
author = "Kasimova, \{Marina A.\} and Debanjan Tewari and John Cowgill and Willy Carrasquel-Ursulaez and Lin, \{Jenna L.\} and Lucie Delemotte and Baron Chanda",
note = "Funding Information: This work was supported by grants from the Gustafsson Foundation and Science for Life Laboratory to LD; National Institutes of Health to B.C. (NS101723), J.C. (T32 HL-07936-18), J.L. (T32 GM008293); Anton 2 allocation to B.C. (PSC17025P and PSC18025P); Romnes faculty fellowship to B.C; Science and Medicine Graduate Research Scholars (SciMed GRS) fellowship to J.L. Preliminary simulations and free energy calculations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at the PDC Centre for High Performance Computing (PDC-HPC). Anton 2 computer time was provided by the Pittsburgh Supercomputing Center (PSC) through Grant R01GM116961 from the National Institutes of Health. The Anton 2 machine at PSC was generously made available by D.E. Shaw Research. The authors declare no competing interests. We would also like to thank N. Nallappan and A. Thangaraju for help generating chimeras and A. Thangaraju, N. Nallappan, and W. Stevens-Sostre for performing frog surgeries. We thank Dr. Yuzuru Itoh for help with the structure refinement and Dr. Rebecca J. Howard for assistance in preparing Figure 2. We would like to thank G.A. Robertson for providing hEAG1, C. Czajkowski for providing the pUNIV vector, B. Santoro and S.A. Siegelbaum for providing mHCN1, and U.B. Kaupp for providing spHCN. We would like to thank S. Chowdhury and other members of the labs for helpful discussions and input throughout the project. Publisher Copyright: {\textcopyright} 2019, eLife Sciences Publications Ltd. All rights reserved.",
year = "2019",
month = nov,
doi = "10.7554/eLife.53400",
language = "English",
volume = "8",
journal = "eLife",
issn = "2050-084X",
}