title: Candida albicans SOU1 encodes a sorbose reductase required for L-sorbose utilization.
abstract: Previous work in our laboratory showed that L-sorbose utilization in Candida albicans is subject to a novel form of regulation which involves a reversible increase or decrease in the copy number of chromosome 5. Furthermore, the structural gene SOU1 is required for L-sorbose utilization and encodes a member of the short chain dehydrogenase family. However, the precise function of SOU1 was not known and neither was the pathway for L-sorbose utilization. We have now expressed SOU1 at a high level from a replicative plasmid having a constitutive ADH1 promoter and purified a version of Sou1p tagged with the FLAG epitope at the N-terminus. Sou1FLAGNp has a sorbose reductase activity which utilizes NADPH as a co-factor and converts L-sorbose to D-sorbitol. It can also less efficiently utilize fructose as a substrate with NADPH as a co-factor, converting fructose to mannitol. In agreement with prediction, the purified enzyme has a subunit molecular weight of 31 kDa and a pI of about 4.8. It probably consists of four identical subunits and has a pH optimum of 6.2. The L-sorbose utilization pathway in C. albicans probably converts L-sorbose to fructose-6-phosphate via D-sorbitol as an intermediate. The first step is catalysed by Sou1p. We also found that C. albicans extracts have a D-sorbitol-6-phosphate dehydrogenase activity, not encoded by SOU1, which utilizes NADP as a co-factor. This activity has not been described previously in yeasts and may be involved in the conversion of phosphorylated D-sorbitol to fructose-6-phosphate or glucose-6-phosphate.
authors.affiliation: Department of Biochemistry and Biophysics, University of Rochester Medical Center, Box 712, Rochester, NY 14642, USA. Jay_Greenberg@urmc.rochester.edu
authors.forename: Jay R
authors.initials: JR
authors.lastname: Greenberg
authors.forename: Neil P
authors.initials: NP
authors.lastname: Price
authors.forename: Richard P
authors.initials: RP
authors.lastname: Oliver
authors.forename: Fred
authors.initials: F
authors.lastname: Sherman
authors.forename: Elena
authors.initials: E
authors.lastname: Rustchenko
mesh_terms: D001483:Base Sequence; D002176:Candida albicans / Q000235:genetics* / Q000378:metabolism*; D004271:DNA, Fungal / Q000235:genetics; D015870:Gene Expression; D005800:Genes, Fungal; D007064:L-Iditol 2-Dehydrogenase / Q000378:metabolism; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D013013:Sorbose / Q000378:metabolism*; D013401:Sugar Alcohol Dehydrogenases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D004271:DNA, Fungal; D012331:RNA, Fungal; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013401:Sugar Alcohol Dehydrogenases; C036132:L-sorbose-1-phosphate reductase; D007064:L-Iditol 2-Dehydrogenase; C022645:sorbitol-6-phosphate dehydrogenase; C506437:sorbose reductase; D013013:Sorbose