Dataset Information

Histoplasma capsulatum proteome response to decreased iron availability.

ABSTRACT:

Background

A fundamental pathogenic feature of the fungus Histoplasma capsulatum is its ability to evade innate and adaptive immune defenses. Once ingested by macrophages the organism is faced with several hostile environmental conditions including iron limitation. H. capsulatum can establish a persistent state within the macrophage. A gap in knowledge exists because the identities and number of proteins regulated by the organism under host conditions has yet to be defined. Lack of such knowledge is an important problem because until these proteins are identified it is unlikely that they can be targeted as new and innovative treatment for histoplasmosis.

Results

To investigate the proteomic response by H. capsulatum to decreasing iron availability we have created H. capsulatum protein/genomic databases compatible with current mass spectrometric (MS) search engines. Databases were assembled from the H. capsulatum G217B strain genome using gene prediction programs and expressed sequence tag (EST) libraries. Searching these databases with MS data generated from two dimensional (2D) in-gel digestions of proteins resulted in over 50% more proteins identified compared to searching the publicly available fungal databases alone. Using 2D gel electrophoresis combined with statistical analysis we discovered 42 H. capsulatum proteins whose abundance was significantly modulated when iron concentrations were lowered. Altered proteins were identified by mass spectrometry and database searching to be involved in glycolysis, the tricarboxylic acid cycle, lysine metabolism, protein synthesis, and one protein sequence whose function was unknown.

Conclusion

We have created a bioinformatics platform for H. capsulatum and demonstrated the utility of a proteomic approach by identifying a shift in metabolism the organism utilizes to cope with the hostile conditions provided by the host. We have shown that enzyme transcripts regulated by other fungal pathogens in response to lowering iron availability are also regulated in H. capsulatum at the protein level. We also identified H. capsulatum proteins sensitive to iron level reductions which have yet to be connected to iron availability in other pathogens. These data also indicate the complexity of the response by H. capsulatum to nutritional deprivation. Finally, we demonstrate the importance of a strain specific gene/protein database for H. capsulatum proteomic analysis.

SUBMITTER: Winters MS

PROVIDER: S-EPMC2645362 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Regulation of iron acquisition genes is critical for microbial survival under both iron-limiting conditions (to acquire essential iron) and iron-replete conditions (to limit iron toxicity). In fungi, iron acquisition genes are repressed under iron-replete conditions by a conserved GATA transcriptional regulator. Here we investigate the role of this transcription factor, Sre1, in the cellular responses of the fungal pathogen Histoplasma capsulatum to iron. We showed that cells in which SRE1 levels were diminished by RNA interference were unable to repress siderophore biosynthesis and utilization genes in the presence of abundant iron, and thus produced siderophores even under iron-replete conditions. Mutation of a GATA-containing consensus site found in the promoters of these genes also resulted in inappropriate gene expression under iron-replete conditions. Microarray analysis comparing control and SRE1-depleted strains under conditions of iron limitation or abundance revealed both iron-responsive genes and Sre1-dependent genes, which comprised distinct but overlapping sets. Iron-responsive genes included putative oxidoreductases, metabolic and mitochondrial enzymes, superoxide dismutase, and nitrosative-stress response genes; Sre1-dependent genes were of diverse function. Genes regulated by iron levels and Sre1 included all of the siderophore biosynthetic genes, a gene involved in reductive iron acquisition, an iron-responsive transcription factor, and two catalases. Based on transcriptional profiling and phenotypic analyses, we conclude that Sre1 plays a critical role in the regulation of both traditional iron-responsive genes and iron-independent pathways such as regulation of cell morphology. These data highlight the evolving realization that the effect of Sre1 orthologs on fungal biology extends beyond the iron regulon. For microarray studies, initial cultures of HcLH120 (Control RNAi-1) or 123 (SRE1 RNAi-2) yeast cells were grown in 5 mL HMM, and then passaged 1:25 into 100 mL HMM. After 2 days of growth, the cultures were pelleted, washed in 100 mL of PBS, resuspended in 100 mL of mRPMI pH 6.5 and diluted to an OD600~2 in 1 L of mRPMI. After 24 hours of growth, 200 mL of culture was harvested for each of the three zero time points. Then the cultures were split into 2 X 400 mL, and 10 uM FeSO4 (final concentration) was added to one set of cultures. At each time point (.5, 1, 4, or 8 hours), 100 mL of culture was harvested for RNA extraction.