Definition of the extracellular proteome of pathogenic-phase Histoplasma capsulatum

Area of Science:

• Mycology
• Pathogen Biology
• Proteomics

Background:

• Histoplasma capsulatum is a dimorphic fungal pathogen causing significant respiratory and systemic disease.
• Pathogenic Histoplasma yeast infect, replicate within, and kill host phagocytes, yet virulence factors remain poorly understood.
• Understanding extracellular virulence factors is critical for developing targeted therapies against Histoplasma infections.

Purpose of the Study:

• To comprehensively define the extracellular proteome of pathogenic-phase Histoplasma yeast.
• To identify novel proteins contributing to Histoplasma virulence and host-pathogen interactions.
• To investigate the expression and localization of identified extracellular factors during infection.

Main Methods:

• Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of pathogenic Histoplasma culture filtrates.
• RNA interference (RNAi)-based depletion for verification of identified extracellular proteins.
• Quantitative reverse transcription PCR (qRT-PCR) to assess gene expression differences between pathogenic yeast and nonpathogenic mycelia.

Main Results:

• Identified 33 deduced extracellular proteins in pathogenic Histoplasma, including known factors like Cbp1 and novel culture filtrate proteins (Cfps).
• Proteins identified include glycanases, oxidative stress defense enzymes, dehydrogenases, and chaperone-like factors.
• Expression of 10 extracellular factors was significantly enriched in pathogenic yeast and observed within macrophages and murine lungs during infection.

Conclusions:

• The extracellular proteome of pathogenic Histoplasma yeast has been characterized, revealing key secreted proteins.
• These identified extracellular proteins are likely involved in Histoplasma pathogenesis and host-pathogen interactions.
• This proteomic dataset provides a foundation for future research into Histoplasma virulence mechanisms.