title: Structural mechanism of plant aquaporin gating.
abstract: Plants counteract fluctuations in water supply by regulating all aquaporins in the cell plasma membrane. Channel closure results either from the dephosphorylation of two conserved serine residues under conditions of drought stress, or from the protonation of a conserved histidine residue following a drop in cytoplasmic pH due to anoxia during flooding. Here we report the X-ray structure of the spinach plasma membrane aquaporin SoPIP2;1 in its closed conformation at 2.1 A resolution and in its open conformation at 3.9 A resolution, and molecular dynamics simulations of the initial events governing gating. In the closed conformation loop D caps the channel from the cytoplasm and thereby occludes the pore. In the open conformation loop D is displaced up to 16 A and this movement opens a hydrophobic gate blocking the channel entrance from the cytoplasm. These results reveal a molecular gating mechanism which appears conserved throughout all plant plasma membrane aquaporins.
authors.affiliation: Department of Chemistry and Bioscience, Chalmers University of Technology, P O Box 462, SE-40530 Göteborg, Sweden.
authors.forename: Susanna
authors.initials: S
authors.lastname: Törnroth-Horsefield
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
authors.forename: Kristina
authors.initials: K
authors.lastname: Hedfalk
authors.forename: Urban
authors.initials: U
authors.lastname: Johanson
authors.forename: Maria
authors.initials: M
authors.lastname: Karlsson
authors.forename: Emad
authors.initials: E
authors.lastname: Tajkhorshid
authors.forename: Richard
authors.initials: R
authors.lastname: Neutze
authors.forename: Per
authors.initials: P
authors.lastname: Kjellbom
mesh_terms: D020346:Aquaporins / Q000737:chemistry* / Q000378:metabolism*; D003198:Computer Simulation; D015640:Ion Channel Gating; D008958:Models, Molecular; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D018724:Spinacia oleracea / Q000737:chemistry* / Q000378:metabolism; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction
chemical_list: D020346:Aquaporins; D010940:Plant Proteins; D010768:Phosphoserine