A YEAST RECOMBINANT AQUAPORIN MUTANT THAT IS NOT EXPRESSED OR MISTARGETED IN XENOPUS OOCYTE CAN BE FUNCTIONALLY ANALYZED IN RECONSTITUTED PROTEOLIPOSOMES

We have recently identified AQPcic (for aquaporin cicadella), an insec t aquaporin found in the digestive tract of homopteran insects and inv olved in the elimination of water ingested in excess with the dietary sap (Le Caherec, F,, Deschamps, S,, Delamarche, C,, Pellerin, I., Bonn ec, G,, Guillam, M, T,, Gouranton, J,, Thomas, D,, and Hubert, J, F, ( 1996) fur. J, Biochem, 241, 707-715), Like many other aquaporins, AQPc ic is inhibited by mercury reagents. In this study, we have demonstrat ed that residue Cys(82) is essential for mercury inhibition. Another m utant version of AQPcic (AQP-C134S), expression of which in Xenopus la evis failed to produce an active molecule, was successfully expressed in Saccharomyces cerevisiae, Using stopped-flow analysis of reconstitu ted proteoliposomes, we demonstrated that the biological activity and Hg sensitivity of yeast-expressed wild type and mutant type AQPcic was readily assessed. Therefore, we propose that the yeast system is a va lid alternative to Xenopus oocytes for studying particular mutants of aquaporin.