A family of oligopeptide transporters is required for growth of Candida albicans on proteins

Abstract

SummaryThe human fungal pathogen Candida albicans can use proteins as the sole source of nitrogen for growth. The secretion of aspartic proteinases, which have been shown to contribute to virulence of C. albicans , allows the fungus to digest host proteins to produce peptides that must be taken up into the cell by specific transporters. To understand in more detail how C. albicans utilizes proteins as a nitrogen source, we undertook a comprehensive analysis of oligopeptide transporters encoded in the C. albicans genome. We identified eight OPT genes encoding putative oligopeptide transporters, almost all of which are represented by polymorphic alleles in strain SC5314. Expression of these genes was differentially induced when C. albicans was grown in YCB-BSA medium, which contains bovine serum albumin as the sole nitrogen source. Whereas deletion of single OPT genes in strain SC5314 did not affect its ability to utilize proteins as a nitrogen source, opt123 D triple mutants had a severe growth defect in YCB-BSA which was rescued by reintroduction of a single copy of OPT1 , OPT2 or OPT3 . In addition, forced expression of OPT4 or OPT5 under control of the ADH1 promoter also restored growth of an opt123 D mutant, demonstrating that at least OPT1-OPT5 encode functional peptide transporters. The various oligopeptide transporters differ in their substrate preferences, as shown by the ability of strains expressing specific OPT genes to grow on peptides of defined length and sequence. We present evidence that in addition to the known role of oligopeptide transporters in the uptake of tetra-and pentapeptides these proteins can also transport longer peptides up to at least eight amino acids in length, ensuring an efficient utilization of the various peptides produced via endoproteolytic digestion of proteins by the secreted aspartic proteinases. As even transporters encoded by polymorphic alleles of a single gene exhibited differences in their efficiency to take up specific peptides, the oligopeptide transporters represent an example for how the evolution of gene families containing differentially expressed and functionally optimized members increases the nutritional versatility and, presumably, the adaptation of C. albicans to different host niches.

Factors Supporting Cysteine Tolerance and Sulfite Production in Candida albicans

“…A P SSU1 -GFP reporter construct was generated as follows: an ApaI-SalI fragment containing SSU1 upstream sequences was amplified from genomic DNA of strain SC5314 with the primers SSU1-1 and SSU1-7, and a PstI-SacI downstream SSU1 fragment was amplified with the primers SSU1-8 and SSU1-4. The upstream and downstream SSU1 fragments were successively cloned via the introduced restriction sites in the plasmid pOPT1G22 (32), resulting in the plasmid pSSU1G2, in which the promoter P SSU1 is fused to the GFP gene.…”

Diverse Hap43-Independent Functions of the Candida albicans CCAAT-Binding Complex

“…Plasmids and primers used for gene manipulation are listed in Tables S3 and S4, respectively. All deletion and reconstituted strains created in this study were generated using the SAT1-FLIP method (17,41,42). DNA fragments used for mutagenesis and complementation were amplified from genomic DNA of strain SC5314.…”

Property Differences among the Four Major Candida albicans Strain Clades

“…These genes were PHO84 (encoding a protein with similarity to high-affinity phosphate transporters; 26), PHO87 (encoding a protein similar to phosphate permeases; 26), PHO100 (encoding an inducible acid phosphatase; 18), and VTC4, (encoding a polyphosphate synthase; GO annotation, CGD). Other genes with expression significantly different between the three virulence groups were cell cycle genes CDC3 (a yeast neck septin; 12, 55) and CDC5 (involved in filamentous growth; 2), MET2 (encoding a homoserine O-acetyltransferase; 16, 52), LAP3 (encoding an aminopeptidase; 27), and oligopeptide transporter-encoding genes IFC1 and IFC3 (31,45). It should be noted (see above) that CA3258, another significant gene in our expression array, was formerly known as IFC2.…”