Abstract
Modal-gating shifts represent an effective regulatory mechanism by which ion channels control the extent and time course of ionic fluxes. Under steady-state conditions, the K+ channel KcsA shows three distinct gating modes, high-Po, low-Po and a high-frequency flicker mode, each with about an order of magnitude difference in their mean open times. Here we show that in the absence of C-type inactivation, mutations at the pore-helix position Glu71 unmask a series of kinetically distinct modes of gating in a side chain–specific way. These gating modes mirror those seen in wild-type channels and suggest that specific interactions in the side chain network surrounding the selectivity filter, in concert with ion occupancy, alter the relative stability of pre-existing conformational states of the pore. The present results highlight the key role of the selectivity filter in regulating modal gating behavior in K+ channels.
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Acknowledgements
We thank F. Bezanilla, L. Cuello, V. Vásquez and H. Raghuraman for insightful discussions; M. Wiener and M. Purdy for crystallographic data collection (for E71Q); the staff of the SER-CAT 22-ID and GM/CA-CAT 23-ID beamlines at the Advanced Photon Source, Argonne National Laboratory, for their invaluable assistance in data collection; R. MacKinnon (Rockefeller University) for providing the KcsA antibody hybridoma cell line; and the US National Center for Supercomputing Applications (NCSA) and the Laboratory Computing Resource Center (LCRC) at Argonne National Laboratory for computer time. This work was supported by US National Institutes of Health grants to E.P. (R01GM057846, U54GM087519) and B.R. (R01GM062342) and by an American Heart Association Postdoctoral Fellowship to S.C.
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S.C., J.F.C.-M. and E.P. designed the research. S.C. and J.F.C.-M. carried out electrophysiology measurements and kinetic analysis. D.M.C. made Fab preparations. J.F.C.-M. and D.M.C. crystallized the mutant proteins. V.J. determined and analyzed the structures. A.C.P. and B.R. did the computation analysis. S.C., J.F.C.-M. and E.P. analyzed the data and wrote the paper.
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Chakrapani, S., Cordero-Morales, J., Jogini, V. et al. On the structural basis of modal gating behavior in K+ channels. Nat Struct Mol Biol 18, 67–74 (2011). https://doi.org/10.1038/nsmb.1968
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DOI: https://doi.org/10.1038/nsmb.1968
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