A single main-chain hydrogen bond required to keep GABAA receptors closed

Borghese, C. M.; Galpin, J. D.; Lidbrink, S. E.; Zhuang, Y.; Desai, N. G.; Howard, R. J.; Lindahl, E.; Ahern, C. A.; Goldschen-Ohm, M. P.

doi:10.1101/2024.12.22.629966

bioRxiv · 10.1101/2024.12.22.629966

A single main-chain hydrogen bond required to keep GABAA receptors closed

Borghese, C. M.·Galpin, J. D.·Lidbrink, S. E.·Zhuang, Y.·Desai, N. G.·Howard, R. J.·Lindahl, E.·Ahern, C. A.·Goldschen-Ohm, M. P.

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Abstract

GABAA receptors are the primary inhibitory neurotransmitter receptors throughout the central nervous system. Despite significant progress understanding their three-dimensional structure, a critical gap remains in determining the molecular basis for channel gating. We recently identified M2-M3 linker mutations that suggest linker flexibility has asymmetric subunit-specific correlations with channel opening. Here we use non-canonical amino acids (ncAAs) to investigate the role of main-chain H-hydrogen bonds (H-bonds) that may stabilize the M2-M3 linkers. We show that a single main-chain H-bond within the {beta}2 subunit M2-M3 linker inhibits pore opening and is required to keep the unliganded channel closed. Furthermore, breaking this H-bond during channel opening accounts for approximately one third of the activation energy derived from GABA binding. In contrast, the analogous H-bond in the 1 subunit has no effect on gating. Our observations suggest that channel opening involves state-dependent breakage/disruption of a specific main-chain H-bond within the {beta}2 subunit M2-M3 linker.

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Borghese, C. M., Galpin, J. D., Lidbrink, S. E., Zhuang, Y., Desai, N. G., Howard, R. J., Lindahl, E., Ahern, C. A., Goldschen-Ohm, M. P.. 2024-12-22. A single main-chain hydrogen bond required to keep GABAA receptors closed. https://doi.org/10.1101/2024.12.22.629966

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