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Nature. 2014 Jan 2;505(7481):56-61. doi: 10.1038/nature12775. Epub 2013 Nov 24.

Structural basis for Ca2+ selectivity of a voltage-gated calcium channel.

Author information

1
1] Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA [2] Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195, USA [3].
2
1] Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA [2].
3
1] Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA [2] Department of Structural Biology, Genentech Inc., South San Francisco, California 94080, USA.
4
Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA.
5
1] Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA [2] Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195, USA.

Abstract

Voltage-gated calcium (CaV) channels catalyse rapid, highly selective influx of Ca(2+) into cells despite a 70-fold higher extracellular concentration of Na(+). How CaV channels solve this fundamental biophysical problem remains unclear. Here we report physiological and crystallographic analyses of a calcium selectivity filter constructed in the homotetrameric bacterial NaV channel NaVAb. Our results reveal interactions of hydrated Ca(2+) with two high-affinity Ca(2+)-binding sites followed by a third lower-affinity site that would coordinate Ca(2+) as it moves inward. At the selectivity filter entry, Site 1 is formed by four carboxyl side chains, which have a critical role in determining Ca(2+) selectivity. Four carboxyls plus four backbone carbonyls form Site 2, which is targeted by the blocking cations Cd(2+) and Mn(2+), with single occupancy. The lower-affinity Site 3 is formed by four backbone carbonyls alone, which mediate exit into the central cavity. This pore architecture suggests a conduction pathway involving transitions between two main states with one or two hydrated Ca(2+) ions bound in the selectivity filter and supports a 'knock-off' mechanism of ion permeation through a stepwise-binding process. The multi-ion selectivity filter of our CaVAb model establishes a structural framework for understanding the mechanisms of ion selectivity and conductance by vertebrate CaV channels.

PMID:
24270805
PMCID:
PMC3877713
DOI:
10.1038/nature12775
[Indexed for MEDLINE]
Free PMC Article

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