Journal Article

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

Rost, Burkhard, Bruni, Renato, Hillerich, Brandan, Love, James, Punta, Marco, Chen, Yu-hang, Hu, Lei, Kloss, Brian, Siegelbaum, Steven A., Hendrickson, Wayne A.

2010

Overview

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. Structure of stomatal anion channel SLAC1 SLAC1 is a recently identified anion channel found in the leaves of plants, where it controls turgor pressure and stomatal opening in response to environmental factors including carbon dioxide, ozone and drought. The X-ray crystal structure of a bacterial homologue of SLAC1 — the tellurite resistance protein TehA from Haemophilus influenzae — has now been determined. Structure-inspired mutagenesis was used to analyse the conductance properties of the channel. Electrostatic features of the pore suggest that selectivity among different anions is largely a function of the energetic cost of ion dehydration. This work, together with further studies of the function of the bacterial protein, suggests that SLAC1 and TehA represent a large family of selective anion channels controlled by environmental stimuli. SLAC1 is a plant ion channel that controls turgor pressure in the guard cells of plant stomata, thereby regulating the exchange of water vapour and photosynthetic gases in response to environmental signals. Here, the X-ray crystal structure of a bacterial homologue of SLAC1 has been solved, and structure-inspired mutagenesis has been used to analyse the conductance properties of the channel. The findings indicate that selectivity among different anions is largely a function of the energetic cost of ion dehydration.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 631/449/2124 / 631/45/269 / 631/535 / Abscisic acid / Amino Acid Sequence / Animals / Anions / Arabidopsis - genetics / Arabidopsis - metabolism / Arabidopsis Proteins - chemistry / Bacteria / Bacterial proteins / Bacterial Proteins - chemistry / Bacterial Proteins - genetics / Bacterial Proteins - metabolism / Biological and medical sciences / Carbon dioxide / Crystalline structure / Crystallography, X-Ray / Crystals / Dehydration / Drought / E coli / Electric Conductivity / Fundamental and applied biological sciences. Psychology / Haemophilus influenzae - chemistry / Haemophilus influenzae - genetics / Hemophilus influenzae / Humanities and Social Sciences / Ion Channel Gating / Ion channels / Membrane Proteins - chemistry / Models, Molecular / Molecular biophysics / Molecular Sequence Data / multidisciplinary / Mutagenesis / Mutation / Oocytes - metabolism / Phenylalanine - chemistry / Phenylalanine - metabolism / Phosphorylation / Plant Stomata - metabolism / Properties / Science / Science (multidisciplinary) / Signal transduction / Static Electricity / Stomata / Structural Homology, Protein / Structure / Structure in molecular biology / Substrate Specificity / Water vapor / Xenopus laevis