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Homologue structure of the SLAC1 anion channel for closing stomata in leaves

Abstract

The plant SLAC1 anion channel controls turgor pressure in the aperture-defining guard cells of plant stomata, thereby regulating the exchange of water vapour and photosynthetic gases in response to environmental signals such as drought or high levels of carbon dioxide. Here we determine the crystal structure of a bacterial homologue (Haemophilus influenzae) of SLAC1 at 1.20 Å resolution, and use structure-inspired mutagenesis to analyse the conductance properties of SLAC1 channels. SLAC1 is a symmetrical trimer composed from quasi-symmetrical subunits, each having ten transmembrane helices arranged from helical hairpin pairs to form a central five-helix transmembrane pore that is gated by an extremely conserved phenylalanine residue. Conformational features indicate a mechanism for control of gating by kinase activation, and electrostatic features of the pore coupled with electrophysiological characteristics indicate that selectivity among different anions is largely a function of the energetic cost of ion dehydration.

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Figure 1: Sequence analysis for the SLAC1 superfamily.
Figure 2: Crystal structure of HiTehA and homology model of AtSLAC1.
Figure 3: Putative structure of the SLAC1 conductance pore.
Figure 4: Ionic conductance measurements.
Figure 5: Structural features at the SLAC1 homologue phenylalanine gate.

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Accession codes

Primary accessions

Protein Data Bank

Data deposits

Atomic coordinates and diffraction data are deposited in the Protein Data Bank with accession codes3M71,3M73,3M74,3M75,3M76, and 3M7L. (See Supplementary Table 4 for identifications.)

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Acknowledgements

We thank F. Mancia, L. Shapiro and M. Zhou for discussions; P. Rodriguez and A. Morrison for help with cloning and expression; J. Cheung, M. Collins, C. Min, S. Ye and Z. Zhang for advice in protein chemistry and crystallography; J. Schwanof and R. Abramowitz for help with synchrotron experiments; J. Riley for help with Xenopus oocyte injections; and M. Su for advice on the PSI-BLAST analysis of SLAC relatives. This project was supported in part by an award to the New York Consortium on Membrane Protein Structure (NYCOMPS) from the NIGMS Protein Structure Initiative. Beamline X4A at the National Synchrotron Light Source (NSLS), a DOE facility at Brookhaven National Laboratory, is supported by the New York Structural Biology Center.

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Y.-H.C., L.H., M.P., R.B., B.H., B.K. and J.L. performed experiments; Y.-H.C., L.H., B.R., S.A.S. and W.A.H. analysed data; Y.-H.C., L.H., S.A.S. and W.A.H. prepared the manuscript.

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Correspondence to Wayne A. Hendrickson.

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The authors declare no competing financial interests.

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Chen, Yh., Hu, L., Punta, M. et al. Homologue structure of the SLAC1 anion channel for closing stomata in leaves. Nature 467, 1074–1080 (2010). https://doi.org/10.1038/nature09487

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