Further study of the Hansenula polymorpha MAL locus: characterization of the alpha-glucoside permease encoded by the HpMAL2 gene.
The HpMAL2 gene of the MAL gene cluster of Hansenula polymorpha codes for a permease similar to yeast maltose and alpha-glucoside transporters. Genomic disruption of HpMAL2 resulted in an inability of cells to grow on maltose, sucrose, trehalose, maltotriose and turanose, as well as a lack of p-nitrophenyl-alpha-D-glucopyranoside (PNPG) transport. PNPG uptake was competitively inhibited by all these substrates, with Ki values between 0.23 and 1.47 mM. Transport by HpMal2p was sensitive to pH and a protonophore carbonyl cyanide-m-chlorophenylhydrazone (CCCP), revealing its energization by the proton gradient over the cell membrane. Although HpMAL2 was responsible for trehalose uptake, its expression was not induced during trehalose growth. A maltase disruption mutant did not grow on maltotriose and turanose, whereas it showed normal growth on trehalose, demonstrating the dispensability of maltase for intracellular hydrolysis of trehalose. In a Genolevures clone pBB0AA011B12, the promoter region and the N-terminal fragment of the putative transactivator of MAL genes is located adjacent to HpMAL2. A reporter gene assay showed that expression from that promoter was induced by maltose and sucrose, repressed by glucose, and derepressed during glycerol and trehalose growth. Therefore, we presume that the gene encodes a functional regulator.
Viigand
Katrin
K
Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia.
Alamäe
Tiina
T
D050260:Carbohydrate Metabolism / Q000235:genetics; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D005656:Fungal Proteins / Q000235:genetics* / Q000502:physiology*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D017930:Genes, Reporter; D005960:Glucosides / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D016254:Mutagenesis, Insertional; D010843:Pichia / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D013379:Substrate Specificity; D015534:Trans-Activators / Q000235:genetics; D014475:Uncoupling Agents / Q000494:pharmacology
D005656:Fungal Proteins; D005960:Glucosides; D026901:Membrane Transport Proteins; D015534:Trans-Activators; D014475:Uncoupling Agents; C019502:4-nitrophenyl alpha-glucoside; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone