2abm

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spinqualitylabelsall models 2abm, resolution 3.20Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

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

Overview

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.

About this Structure

2ABM is a Single protein structure of sequence from Escherichia coli with BGL, PO4, POQ, PEE, 3PG and AGA as ligands. Full crystallographic information is available from OCA.

Reference

Crystal structure of AqpZ tetramer reveals two distinct Arg-189 conformations associated with water permeation through the narrowest constriction of the water-conducting channel., Jiang J, Daniels BV, Fu D, J Biol Chem. 2006 Jan 6;281(1):454-60. Epub 2005 Oct 20. PMID:16239219

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