PMID:16239219
| Citation |
Jiang, J, Daniels, BV and Fu, D (2006) 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. 281:454-60 |
|---|---|
| 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. |
| Links |
PubMed Online version:10.1074/jbc.M508926200 |
| Keywords |
Aquaporins/chemistry; Aquaporins/metabolism; Biological Transport; Crystallography; Escherichia coli; Escherichia coli Proteins/chemistry; Escherichia coli Proteins/metabolism; Membrane Proteins/chemistry; Membrane Proteins/metabolism; Protein Structure, Quaternary; Protein Structure, Secondary; Protein Structure, Tertiary; Water/metabolism |
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