Mosquito (Aedes aegypti) aquaporin, present in tracheolar cells, transports water, not glycerol, and forms orthogonal arrays in Xenopus oocyte membranes

Previous results showed that mRNA encoding a putative aquaporin (AQP) (GenBank accession number AF218314) is present in the tracheolar cells associated with female Aedes aegypti Malpighian tubules. In this study, immunohistochemistry detected the protein, Aea AQP, also in tracheolar cells, suggesting its involvement in water movement in the respiratory system. When expressed in Xenopus oocytes, Aea AQP increased the osmotic water permeability from 15 x 10(-6) to 150 x 10(-6) m.s(-1), which was inhibited by mercury ions. No permeability to glycerol or other solute was observed. Aea AQP expressed in oocytes was solubilized as a homotetramer in nondenaturing detergent as deduced from velocity centrifugation on density gradients. Phylogenetic analysis of MIP (major intrinsic protein) family sequences shows that Aea AQP clusters with other native orthogonal array forming proteins. Specific orthogonal arrays were detected by freeze-fracture analysis of Aea AQP oocyte membranes. We conclude that, in tracheolar cells of A. aegypti , Aea AQP is probably a highly water-permeable homotetrameric MIP which natively can form 2D crystals.