Structural mechanism of plant aquaporin gating.
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.
Törnroth-Horsefield
Susanna
S
Department of Chemistry and Bioscience, Chalmers University of Technology, P O Box 462, SE-40530 Göteborg, Sweden.
Wang
Yi
Y
Hedfalk
Kristina
K
Johanson
Urban
U
Karlsson
Maria
M
Tajkhorshid
Emad
E
Neutze
Richard
R
Kjellbom
Per
P
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
D020346:Aquaporins; D010940:Plant Proteins; D010768:Phosphoserine