2ABM

Crystal Structure of Aquaporin Z Tetramer Reveals both Open and Closed Water-conducting Channels

Summary for 2ABM

• Entry DOI: 10.2210/pdb2abm/pdb
• Related: 1fx8 1rc2
• Descriptor: Aquaporin Z, 2-O-octyl-beta-D-glucopyranose, BIS(((3S,4S,5R,6R)-5-(ETHYL(PHOSPHORYLOXY))-3,4,6-TRIHYDROXY-TETRAHYDRO-2H-PYRAN-2-YL)METHYL) HYDROGEN PHOSPHATE, ... (8 entities in total)
• Functional Keywords: aquaporin, membrane protein
• Biological source: Escherichia coli
• Total number of polymer chains: 8
• Total formula weight: 198420.26

Authors

Jiang, J.,Daniels, B.V.,Fu, D. (deposition date: 2005-07-15, release date: 2005-09-20, Last modification date: 2023-08-23)

Primary citation

Jiang, J.,Daniels, B.V.,Fu, D.
Crystal Structure of AqpZ Tetramer Reveals Two Distinct Arg-189 Conformations Associated with Water Permeation through the Narrowest Constriction of the Water-conducting Channel.
J.Biol.Chem., 281:454-460, 2006

PubMed Abstract: AqpZ is a homotetramer of four water-conducting channels that facilitate rapid water movements across the plasma membrane of Escherichia coli. Here we report a 3.2 angstroms crystal structure of the tetrameric AqpZ (tAqpZ). All channel-lining residues in the four monomeric channels are found orientated in nearly identical positions with one marked exception at the narrowest channel constriction, where the side chain of a highly conserved Arg-189 adopts two distinct conformational orientations. In one of the four monomers, the guanidino group of Arg-189 points toward the periplasmic vestibule, opening up the constriction to accommodate the binding of a water molecule through a tridentate H-bond. In the other three monomers, the Arg-189 guanidino group bends over to form an H-bond with carbonyl oxygen of the Thr-183, thus occluding the channel. Therefore, the tAqpZ structure reveals two distinct Arg-189 confirmations associated with water permeation through the channel constrictions. Alternation between the two Arg-189 conformations disrupts continuous flow of water, thus regulating the open probability of the water pore. Further, the difference in Arg-189 displacements is correlated with a strong electron density found between the first transmembrane helices of two open channels, suggesting that the observed Arg-189 conformations are stabilized by asymmetrical subunit interactions in tAqpZ.

PubMed: 16239219
DOI: 10.1074/jbc.M508926200

Experimental method

X-RAY DIFFRACTION (3.2 Å)