Water permeability and characterization of aquaporin-11.
The water permeability of aquaporin-11 (AQP11), which has a cysteine substituted for an alanine at a highly conserved asparagine-proline-alanine (NPA) motif in the water channel family, is controversial. Our previous study, however, showed that AQP11 is water permeable in proteoliposomes in which AQP11 molecules were reconstituted after purification with Fos-choline 10, which is the most suitable detergent available for stable solubilization of AQP11. In our previous study, we were unable to exclude the effect of the detergent on the water conductance. Therefore, in the present study, we measured the water permeability of AQP11 without detergent using vesicles that directly formed from Sf9 cell membranes expressing AQP11 molecules. The water permeability of AQP11 was 8-fold lower than that of AQP1 and 3-fold higher than that of mock-infected cell membrane, and was reversibly inhibited by mercury ions. Considering the slow but constant water permeable functions of AQP11, we performed homology modeling to search for a common structural feature. When comparing our model with those of other AQP structures, we found that Tyr83 facing the channel pore might be a key amino acid residue that decreases the water permeation of AQP11. Our findings indicate that AQP11 could be involved in slow but constant water movement across the membrane.
Department of Biophysics, Graduate School of Science, Kyoto University, Oiwake, Kitashirakawa, Sakyo-ku, Kyoto 606 8502, Japan.
Kaya
K
Yakata
Kazutoshi
K
Tani
Yoshinori
Y
Fujiyoshi
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D051398:Aquaporin 1 / Q000737:chemistry / Q000378:metabolism; D051401:Aquaporin 4 / Q000737:chemistry / Q000378:metabolism; D020346:Aquaporins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D017124:Conserved Sequence; D006801:Humans; D008627:Mercuric Chloride / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010539:Permeability; D017434:Protein Structure, Tertiary; D051381:Rats; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D040681:Structural Homology, Protein; D014867:Water / Q000378:metabolism*
C496020:AQP1 protein, human; C503878:Aqp11 protein, mouse; C496032:Aqp4 protein, rat; D051401:Aquaporin 4; D020346:Aquaporins; D014867:Water; D051398:Aquaporin 1; D008627:Mercuric Chloride