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Redundancy, phylogeny and differential expression of Histoplasma capsulatum catalases
Clayton H Johnson1,2, Martin G Klotz3, J Lyndal York1
1Donald W. Reynolds Dept of Geriatrics2, Department of Microbiology and Immunology3, and Department of Biochemistry and Molecular Biology4, University of Arkansas for Medical Sciences, 4301 W Markham St, Little Rock, AR 72205, USA.
Abstract:
Histoplasma capsulatum produces an extracellular catalase termed M antigen, which is similar to catalase B of Aspergillus and Emericella species. Evidence is presented here for two additional catalase isozymes in H. capsulatum. Catalase A is highly similar to a large-subunit catalase in Aspergillus and Emericella species, while catalase P is a small-subunit catalase protein with greatest similarity to known peroxisomal catalases of animals and Saccharomycotina yeasts. Complete cDNAs for the CATA and CATP genes (encoding catalases A and P, respectively) were isolated. The transcriptional expression of the H. capsulatum CATA, CATB (M antigen) and CATP genes was assessed by Northern blot hybridizations on total RNA. Results at the transcript levels for these genes are shown for three conditions: cell morphology (mycelial versus yeast phase cells), oxidative stress (in response to a challenge with H(2)O(2)) and carbon source (glucose vs glycerol). Collectively, these results demonstrated regulation of CATA by both cell morphology and oxidative stress, but not by carbon source, and regulation of CATB and CATP by carbon source but not cell morphology or oxidative stress. A phylogenetic analysis of presently available catalase sequences and intron residences was done. The results support a model for evolution of eukaryotic monofunctional catalase genes from prokaryotic genes.
Insights
Histoplasma capsulatum possesses three catalase isozymes, including M antigen, Catalase A, and Catalase P. Their gene expression is differentially regulated by cell morphology, oxidative stress, and carbon source.
Area of Science:
- Biochemistry
- Molecular Biology
- Mycology
Background:
- Histoplasma capsulatum, a dimorphic fungus, produces an extracellular catalase (M antigen) similar to Aspergillus catalase B.
- Previous studies identified M antigen but lacked comprehensive analysis of other catalase isozymes in H. capsulatum.
Purpose of the Study:
- To identify and characterize additional catalase isozymes in Histoplasma capsulatum.
- To investigate the transcriptional regulation of H. capsulatum catalase genes (CATA, CATB, CATP) under varying conditions.
Main Methods:
- Isolation of complete cDNAs for CATA and CATP genes.
- Northern blot analysis of total RNA to assess transcript levels.
- Phylogenetic analysis of catalase sequences and intron positions.
Main Results:
- Two additional catalase isozymes, Catalase A (large-subunit) and Catalase P (small-subunit), were identified.
- CATA gene expression is regulated by cell morphology and oxidative stress.
- CATB and CATP gene expression are regulated by carbon source, independent of cell morphology or oxidative stress.
Conclusions:
- H. capsulatum exhibits a complex catalase system with distinct regulatory mechanisms.
- The findings support a model for the evolution of eukaryotic monofunctional catalase genes from prokaryotic origins.