Isolation of cDNA clones coding for peroxisomal proteins of Candida tropicalis: identification and sequence of a clone for catalase

Systems biology at the Institute for Systems Biology

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An n-alkane-responsive promoter element found in the gene encoding the peroxisomal protein of Candida tropicalis does not contain a C(6) zinc cluster DNA-binding motif

When an asporogenic diploid yeast, Candida tropicalis, is cultivated on n-alkane, the expression of the genes encoding enzymes of the peroxisomal beta-oxidation pathway is highly induced. An upstream activation sequence (UAS) which can induce transcription in response to n-alkane (UAS(ALK)) was identified on the promoter region of the peroxisomal 3-ketoacyl coenzyme A (CoA) thiolase gene of C. tropicalis (CT-T3A). The 29-bp region (from -289 to -261) present upstream of the TATA sequence was sufficient to induce n-alkane-dependent expression of a reporter gene. Besides n-alkane, UAS(ALK)-dependent gene expression also occurred in the cells grown on oleic acid. Several kinds of mutant UAS(ALK) were constructed and tested for their UAS activity. It was clarified that the important nucleotides for UAS(ALK) activity were located within 10-bp region from -273 to -264 (5'-TCCTGCACAC-3'). This region did not contain a CGG triplet and therefore differed from the sequence of the oleate-response element (ORE), which is a UAS found on the promoter region of 3-ketoacyl-CoA thiolase gene of Saccharomyces cerevisiae. Similar sequences to UAS(ALK) were also found on several peroxisomal enzyme-encoding genes of C. tropicalis.

Antioxidant systems in the pathogenic fungi of man and their role in virulence

In the last two decades, a variety of fungal antioxidants have attracted considerable interest, largely arising from their hypothetical role as virulence determinants. Melanin is a potent free radical scavenger and in Cryptococcus neoformans, there is now good evidence that the production of melanin is a significant virulence determinant. There is also recent evidence linking melanin biosynthesis to the virulence of Aspergillus fumigatus conidia. Superoxide dismutases are important housekeeping antioxidants and have an additional hypothetical role in virulence; however, although these enzymes have been biochemically characterized from Aspergillus and Cryptococcus, there is as yet no firm evidence that these enzymes are involved in pathogenicity. Catalase production may play some role in the virulence of Candida albicans but this enzyme has not been shown, as yet, to influence the virulence of A. fumigatus. There are some data supporting an antioxidant function for the acyclic hexitol mannitol in C. neoformans, but further investigations are required in this area. Research into the putative antioxidant activities of a range of other fungal enzymes, such as acid phosphatases, remains limited at this time.

Production of lactones and peroxisomal beta-oxidation in yeasts

Among aroma compounds interesting for the food industry, lactones may be produced by biotechnological means using yeasts. These microorganisms are able to synthesize lactones de novo or by biotransformation of fatty acids with higher yields. Obtained lactone concentrations are compatible with industrial production, although detailed metabolic pathways have not been completely elucidated. The biotransformation of ricinoleic acid into gamma-decalactone is taken here as an example to better understand the uptake of hydroxy fatty acids by yeasts and the different pathways of fatty acid degradation. The localization of ricinoleic acid beta-oxidation in peroxisomes is demonstrated. Then the regulation of the biotransformation is described, particularly the induction of peroxisome proliferation and peroxisomal beta-oxidation and its regulation at the genome level. The nature of the biotransformation product is then discussed (4-hydroxydecanoic acid or gamma-decalactone), because the localization and the mechanisms of the lactonization are still not properly known. Lactone production may also be limited by the degradation of this aroma compound by the yeasts which produced it. Thus, different possible ways of modification and degradation of gamma-decalactone are described.

Assignment of most genes encoding major peroxisomal polypeptides to chromosomal band V of the asporogenic yeast Candida tropicalis

The peroxisomes of the asporogenic yeast Candida tropicalis contain about 20 major polypeptides (PXPs). We have isolated a number of genes encoding them; 11 POX genes encoded independent PXPs and three POY genes were likely to encode three other PXPs. To locate these genes on the chromosomes, chromosomes of C. tropicalis were separated by pulsed-field gel electrophoresis. Eight chromosomal bands were observed over the range of 1.0 Mbp (band 1) to 2.8 Mbp (band VIII); the genome size was estimated to be about 20 Mbp. Southern blot analysis showed that ten genes were on band V, three genes were on band IV, and the other gene was on band VI. Three genes gave hybridization signals of nearly equal intensity on two different chromosomal bands: POX6A and POX8B, on bands V and VII; and POX8A, on bands IV and VI. Ribosomal RNA genes also hybridized to two bands, VI and VII. Most genes assigned to only one band hybridized to two restriction fragments produced by either NotI or SfiI endonuclease. The results suggested that C. tropicalis was diploid and that restriction sites were conserved little between homologues. The three POX genes that were found on two chromosomal bands hybridized to not more than two restriction fragments, implying that the allelic genes were present on different chromosomal bands.

The nucleotide sequence of POX18, a gene encoding a small oleate-inducible peroxisomal protein from Candida tropicalis

We report the molecular cloning and nucleotide sequence of the nuclear gene, POX18, encoding an oleate-inducible peroxisomal protein from the yeast Candida tropicalis. POX18 has a single open reading frame of 381 nucleotides (nt), which encodes a protein of 127 amino acids. The predicted Mr of this protein is 13,792. Codon usage in the expression of POX18 is non-random, and shows a pattern similar to that used for other peroxisomal genes from C. tropicalis and highly expressed genes from Saccharomyces cerevisiae. Northern analysis of total RNA from oleate-grown cells determined that POX18 mRNA is approximately 750 nt in length. The POX18 gene was expressed in vitro, which resulted in a single translation product that co-migrated in denaturing polyacrylamide gels with an abundant peroxisomal protein (apparent mass of 16 kDa) and was immunoprecipitated by an antiserum against peroxisomal protein.

cDNA cloning and primary structure determination of the peroxisomal trifunctional enzyme hydratase-dehydrogenase-epimerase from the yeast Candida tropicalis pK233

We report the isolation and nucleotide (nt) sequence determination of a cDNA encoding the peroxisomal trifunctional beta-oxidation enzyme hydratase-dehydrogenase-epimerase (HDE) from the yeast Candida tropicalis pK233. Poly(A)+RNA isolated from C. tropicalis cells grown in oleic acid medium was used to construct a cDNA library in lambda gt11. The library was screened with a polyclonal antiserum against HDE. A recombinant was confirmed to encode HDE by hybridization-selection translation and immunoprecipitation. The HDE cDNA (HDE) has a single open reading frame of 2718 nt, encoding a protein of 905 amino acids, not including the initiator methionine. The Mr of the protein is 99,350. A partial gene duplication is believed to have occurred in the evolution of the HDE gene. Codon utilization in the gene is not random, with 86.0% of the amino acids specified by 23 preferentially used codons, a situation similar to that found in genes encoding peroxisomal catalase and the various fatty acyl-CoA oxidases from C. tropicalis. The increase in HDE activity in C. tropicalis cells grown in oleic acid medium as opposed to glucose medium is due, at least in part, to increased HDE-specific mRNA levels.

Sequence of the Saccharomyces cerevisiae CTA1 gene and amino acid sequence of catalase A derived from it

The nucleotide sequence of a 2785-base-pair stretch of DNA containing the Saccharomyces cerevisiae catalase A (CTA1) gene has been determined. This gene contains an uninterrupted open reading frame encoding a protein of 515 amino acids (relative molecular mass 58,490). Catalase A, the peroxisomal catalase of S. cerevisiae was compared to the peroxisomal catalases from bovine liver and from Candida tropicalis and to the non-peroxisomal, presumably cytoplasmic, catalase T of S. cerevisiae. Whereas the peroxisomal catalases are almost colinear, three major insertions have to be introduced in the catalase T sequence to obtain an optimal fit with the other proteins. Catalase A is most closely related to the C. tropicalis enzyme. It is also more similar to the bovine liver catalase than to the second S. cerevisiae catalase. The differences between the two S. cerevisiae enzymes are most striking within four blocks of amino acids consisting of a total of 37 residues with high homology between the three peroxisomal, but low conservation between the S. cerevisiae catalases. The results obtained indicate that the peroxisomal catalases compared have very similar three-dimensional structures and might have similar targeting signals.

The nucleotide sequence of complementary DNA and the deduced amino acid sequence of peroxisomal catalase of the yeast Candida tropicalis pK233

We report the isolation and nucleotide (nt) sequence determination of cDNA encoding peroxisomal catalase (Cat) from the yeast Candida tropicalis pK233. The catalase cDNA (Cat) has a single open reading frame (ORF) of 1455 nt, encoding a protein of 484 amino acids (aa), not including the initiator methionine. The Mr of the protein is 54767. Codon use in the gene is not random, with 90.9% of the aa specified by 25 principal codons. The principal codons used in the expression of Cat in C. tropicalis are similar to those used in the expression of the fatty acyl-CoA oxidase gene of C. tropicalis and of highly expressed genes in Saccharomyces cerevisiae. Cat shows 48.0%, 49.7%, and 48.3% aa identity with human, bovine, and rat catalases, respectively, and 44.3% aa identity with catalase T of S. cerevisiae. The 3 aa of bovine liver catalase previously postulated to participate in catalysis and 79.5% of those aa in the immediate environment of hemin, the prosthetic group of catalase, are conserved in Cat of C. tropicalis.