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X-ray structure of a ClC chloride channel at 3.0 Å reveals the molecular basis of anion selectivity

Abstract

The ClC chloride channels catalyse the selective flow of Cl- ions across cell membranes, thereby regulating electrical excitation in skeletal muscle and the flow of salt and water across epithelial barriers. Genetic defects in ClC Cl- channels underlie several familial muscle and kidney diseases. Here we present the X-ray structures of two prokaryotic ClC Cl- channels from Salmonella enterica serovar typhimurium and Escherichia coli at 3.0 and 3.5 Å, respectively. Both structures reveal two identical pores, each pore being formed by a separate subunit contained within a homodimeric membrane protein. Individual subunits are composed of two roughly repeated halves that span the membrane with opposite orientations. This antiparallel architecture defines a selectivity filter in which a Cl- ion is stabilized by electrostatic interactions with α-helix dipoles and by chemical coordination with nitrogen atoms and hydroxyl groups. These findings provide a structural basis for further understanding the function of ClC Cl- channels, and establish the physical and chemical basis of their anion selectivity.

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Figure 1: Sequence alignment of ClC channels.
Figure 2: Experimental electron density.
Figure 3: Structure of the StClC dimer.
Figure 4: Structure of the StClC subunit.
Figure 5: Structure of the StClC selectivity filter.
Figure 6: Ion conduction pathway.
Figure 7: Two architectures for ion-channel proteins.

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Acknowledgements

We thank M. Becker and L. Berman at the National Synchrotron Light Source X-25, the staff at the Cornell High Energy Synchrotron Source A1 and F1, and C. Petosa and A. Perrakis of the European Molecular Biology Laboratory at the European Synchrotron Radiation Facility ID-13 for assistance in data collection; J. Bonanno for technical assistance; members of the MacKinnon laboratory for assistance at all stages of the project; and S. Harrison, D. Jeruzalmi, A. Phillippsen and O. Andersen for discussions. This work was supported by grants from the National Institutes of Health (NIH) to R.M. and from the National Center for Research Resources, NIH, to B.T.C. R.M. is an investigator in the Howard Hughes Medical Institute.

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Correspondence to Roderick MacKinnon.

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Dutzler, R., Campbell, E., Cadene, M. et al. X-ray structure of a ClC chloride channel at 3.0 Å reveals the molecular basis of anion selectivity. Nature 415, 287–294 (2002). https://doi.org/10.1038/415287a

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