The activity of the glyoxylate cycle in peroxisomes of Candida albicans depends on a functional beta-oxidation pathway: evidence for reduced metabolite transport across the peroxisomal membrane.
The glyoxylate cycle, a metabolic pathway required for generating C(4) units from C(2) compounds, is an important factor in virulence, in both animal and plant pathogens. Here, we report the localization of the key enzymes of this cycle, isocitrate lyase (Icl1; EC 4.1.3.1) and malate synthase (Mls1; EC 2.3.3.9), in the human fungal pathogen Candida albicans. Immunocytochemistry in combination with subcellular fractionation showed that both Icl1 and Mls1 are localized to peroxisomes, independent of the carbon source used. Although Icl1 and Mls1 lack a consensus type I peroxisomal targeting signal (PTS1), their import into peroxisomes was dependent on the PTS1 receptor Pex5p, suggesting the presence of non-canonical targeting signals in both proteins. Peroxisomal compartmentalization of the glyoxylate cycle is not essential for proper functioning of this metabolic pathway because a pex5Delta/Delta strain, in which Icl1 and Mls1 were localized to the cytosol, grew equally as well as the wild-type strain on acetate and ethanol. Previously, we reported that a fox2Delta/Delta strain that is completely deficient in fatty acid beta-oxidation, but has no peroxisomal protein import defect, displayed strongly reduced growth on non-fermentable carbon sources such as acetate and ethanol. Here, we show that growth of the fox2Delta/Delta strain on these carbon compounds can be restored when Icl1 and Mls1 are relocated to the cytosol by deleting the PEX5 gene. We hypothesize that the fox2Delta/Delta strain is disturbed in the transport of glyoxylate cycle products and/or acetyl-CoA across the peroxisomal membrane and discuss the possible relationship between such a transport defect and the presence of giant peroxisomes in the fox2Delta/Delta mutant.
Piekarska
Katarzyna
K
Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
Hardy
Guy
G
Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
Mol
Els
E
Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
van den Burg
Janny
J
Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
Strijbis
Karin
K
Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
van Roermund
Carlo
C
Department of Genetic Metabolic Diseases, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
van den Berg
Marlene
M
Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
Distel
Ben
B
Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
D015094:3-Hydroxyacyl CoA Dehydrogenases; D002176:Candida albicans / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D003600:Cytosol / Q000378:metabolism; D004746:Enoyl-CoA Hydratase; D000431:Ethanol / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D017353:Gene Deletion; D005800:Genes, Fungal; D006038:Glyoxylates / Q000378:metabolism*; D007522:Isocitrate Lyase / Q000378:metabolism*; D008292:Malate Synthase / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D019301:Oleic Acid / Q000378:metabolism; D010084:Oxidation-Reduction; D000074435:Peroxisome-Targeting Signal 1 Receptor; D020675:Peroxisomes / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
D005656:Fungal Proteins; D006038:Glyoxylates; C000614264:PEX5 protein, human; D000074435:Peroxisome-Targeting Signal 1 Receptor; D018160:Receptors, Cytoplasmic and Nuclear; D029701:Saccharomyces cerevisiae Proteins; D019301:Oleic Acid; D000431:Ethanol; D015094:3-Hydroxyacyl CoA Dehydrogenases; D008292:Malate Synthase; C542285:ICL1 protein, S cerevisiae; D007522:Isocitrate Lyase; D004746:Enoyl-CoA Hydratase; C073759:FOX2 protein, S cerevisiae