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Secreted dipeptidyl peptidase IV activity in the dimorphic fungal pathogen Histoplasma capsulatum

Kendal G Cooper1, Jon P Woods

  • 1Department of Medical Microbiology and Immunology, University of Wisconsin, Madison, WI 53706, USA.

Infection and Immunity
|April 8, 2009
PubMed

Insights

Histoplasma capsulatum secretes dipeptidyl peptidase type IV (DppIV) activity. Unexpectedly, HcDPPIVB, not HcDPPIVA, is responsible for this secreted DppIV activity in the fungus.

Area of Science:

  • Mycology
  • Enzymology
  • Molecular Biology

Background:

  • Dipeptidyl peptidase type IV (DppIV) enzymes have diverse roles in biological systems.
  • Histoplasma capsulatum, a fungal pathogen, exhibits secreted proteolytic activity against DppIV substrates.

Purpose of the Study:

  • To identify the specific gene(s) responsible for the secreted DppIV activity in Histoplasma capsulatum.
  • To investigate the roles of two putative DppIV homologs, HcDPPIVA and HcDPPIVB, in this secreted activity.

Main Methods:

  • Homology search to identify DppIV homologs in H. capsulatum.
  • Comparative sequence analysis of identified homologs.
  • RNA interference (RNAi) silencing and gene deletion to assess the function of HcDPPIVA and HcDPPIVB.
  • Assay of secreted DppIV activity.
  • Macrophage killing assays.

Main Results:

  • Two putative DppIV homologs, HcDPPIVA and HcDPPIVB, were identified in H. capsulatum.
  • HcDPPIVA showed similarity to secreted DppIV enzymes, while HcDPPIVB clustered with intracellular enzymes.
  • Silencing or deletion of HcDPPIVA did not affect secreted DppIV activity.
  • RNAi silencing of HcDPPIVB significantly reduced secreted DppIV activity.
  • HcDPPIVB was not required for H. capsulatum's ability to kill macrophages.

Conclusions:

  • The gene encoding the secreted DppIV activity in H. capsulatum is HcDPPIVB, contrary to initial expectations based on sequence homology.
  • HcDPPIVA does not contribute to the secreted DppIV activity.
  • HcDPPIVB is not essential for the virulence of H. capsulatum in macrophage infection models.

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