Characterization of thioredoxin reductase genes (trr1) from Pneumocystis carinii and Pneumocystis jiroveci

Complementation of a manganese-dependent superoxide dismutase-deficient yeast strain with Pneumocystis carinii sod2 gene

Manganese-dependent superoxide dismutase (MnSOD) is one of the key enzymes involved in the cellular defense against oxidative stress. Previously, the Pneumocystis carinii sod2 gene (Pcsod2) was isolated and characterized. Based on protein sequence comparison, Pcsod2 was suggested to encode a putative MnSOD protein likely to be targeted into the mitochondrion. In this work, the Pcsod2 was cloned and expressed as a recombinant protein in EG110 Saccharomyces cerevisiae strain lacking the MnSOD-coding gene (Scsod2) in order to investigate the function and subcellular localization of P. carinii MnSOD (PcMnSOD). The Pcsod2 gene was amplified by PCR and cloned into the pYES2.1/V5-His-TOPO(®) expression vector. The recombinant construct was then transformed into EG110 strain. Once its expression had been induced, PcMnSOD was able to complement the growth defect of EG110 yeast cells that had been exposed to the redox-cycling compound menadione. N-term sequencing of the PcMnSOD protein allowed identifying the cleavage site of a mitochondrial targeting peptide. Immune-colocalization of PcMnSOD and yeast CoxIV further confirmed the mitochondrial localization of the PcMnSOD. Heterologous expression of PcMnSOD in yeast indicates that Pcsod2 encodes an active MnSOD, targeted to the yeast mitochondrion that allows the yeast cells to grow in the presence of reactive oxygen species (ROS).

Pneumocystis jirovecii multilocus gene sequencing: findings and implications

Pneumocystis jirovecii pneumonia (PcP) remains a major cause of respiratory illness among immunocompromised patients, especially patients infected with HIV, but it has also been isolated from immunocompetent persons. This article discusses the application of multilocus genotyping analysis to the study of the genetic diversity of P. jirovecii and its epidemiological and clinical parameters, and the important concepts achieved to date with these approaches. The multilocus typing studies performed until now have shown that there is an important genetic diversity of stable and ubiquitous P. jirovecii genotypes; infection with P. jirovecii is not necessarily clonal, recombination between some P. jirovecii multilocus genotypes has been suggested. P. jirovecii-specific multilocus genotypes can be associated with severity of PcP. Patients infected with P. jirovecii, regardless of the form of infection they present with, are part of a common human reservoir for future infections. The CYB, DHFR, DHPS, mtLSU rRNA, SOD and the ITS loci are suitable genetic targets to be used in further epidemiological studies focused on the identification and characterization of P. jirovecii haplotypes correlated with drug resistance and PcP outcome.

Thioredoxin reductase is essential for viability in the fungal pathogen Cryptococcus neoformans

Thioredoxin reductase (TRR1) is an important component of the thioredoxin oxidative stress resistance pathway. Here we show that it is induced during oxidative and nitrosative stress and is preferentially localized to the mitochondria in Cryptococcus neoformans. The C. neoformans TRR1 gene encodes the low-molecular-weight isoform of the thioredoxin reductase enzyme, which shares little homology with that of its mammalian host. By replacing the endogenous TRR1 promoter with an inducible copper transporter promoter, we showed that Trr1 appears to be essential for viability of this pathogenic fungus, making it a potential antifungal target.

Gene arrays at Pneumocystis carinii telomeres

In the fungus Pneumocystis carinii, at least three gene families (PRT1, MSR, and MSG) have the potential to generate high-frequency antigenic variation, which is likely to be a strategy by which this parasitic fungus is able to prolong its survival in the rat lung. Members of these gene families are clustered at chromosome termini, a location that fosters recombination, which has been implicated in selective expression of MSG genes. To gain insight into the architecture, evolution, and regulation of these gene clusters, six telomeric segments of the genome were sequenced. Each of the segments began with one or more unique genes, after which were members of different gene families, arranged in a head-to-tail array. The three-gene repeat PRT1-MSR-MSG was common, suggesting that duplications of these repeats have contributed to expansion of all three families. However, members of a gene family in an array were no more similar to one another than to members in other arrays, indicating rapid divergence after duplication. The intergenic spacers were more conserved than the genes and contained sequence motifs also present in subtelomeres, which in other species have been implicated in gene expression and recombination. Long mononucleotide tracts were present in some MSR genes. These unstable sequences can be expected to suffer frequent frameshift mutations, providing P. carinii with another mechanism to generate antigen variation.