Aquaporins in Saccharomyces: Characterization of a second functional waterchannel protein

The Saccharomyces cerevisiae genome database contains two ORFs with homolog y to aquaporins, AQY1 and AQY2. Aqy1p has been shown to be a functional aqu aporin in some strains, such as Sigma 1278b. AQY2 is disrupted by a stop co don in most strains; however, Sigma 1278b has an intact ORF. Because Sigma 1278b Aqy2p has an intracellular localization in Xenopus oocytes and in yea st, other strains of yeast were examined. Aqy2p from Saccharomyces chevalie ri has a single amino acid in the third transmembrane domain (Ser-141) that differs from Sigma 1278b Aqy2p (Pro-141). S. chevalieri Aqy2p is a functio nal water channel in oocytes and traffics to the plasma membrane of yeast. The Sigma 1278b parental strain, the aqy1-aqy2 double null yeast, and null yeast expressing S. chevalieri Aqy2p were examined under various conditions . Comparison of these strains revealed that the aquaporin null cells were m ore aggregated and their surface was more hydrophobic. As a result, the aqu aporin null cells were more flocculent and more efficient at haploid invasi ve growth. Despite its primary intracellular localization, Sigma 1278b Aqy2 p plays a role in yeast similar to Aqy1p and S. chevalieri Aqy2p. In additi on, Aqy1p and Aqy2p can affect cell surface properties and may provide an a dvantage by dispersing the cells during starvation or during sexual reprodu ction.