Biological Function and Molecular Mapping of M Antigen in Yeast Phase of Histoplasma capsulatum

Histoplasmosis, due to the intracellular fungus Histoplasma capsulatum, can be diagnosed by demonstrating the presence of antibodies specific to the immunodominant M antigen. However, the role of this protein in the pathogenesis of histoplasmosis has not been elucidated. We sought to structurally and immunologically characterize the protein, determine yeast cell surface expression, and confirm catalase activity. A 3D-rendering of the M antigen by homology modeling revealed that the structures and domains closely resemble characterized fungal catalases. We generated monoclonal antibodies (mAbs) to the protein and determined that the M antigen is present on the yeast cell surface and in cell wall/cell membrane preparations. Similarly, we found that the majority of catalase activity was in extracts containing fungal surface antigens and that the M antigen is not significantly secreted by live yeast cells. The mAbs also identified unique epitopes on the M antigen. The localization of the M antigen to the cell surface of H. capsulatum yeast and the characterization of the protein's major epitopes have important implications since it demonstrates that although the protein may participate in protecting the fungus against oxidative stress it is also accessible to host immune cells and antibody

Applications of Structural Biology and Bioinformatics in the Investigation of Oxidative Stress-Related Processes

Reactive oxygen species (ROS)-mediated dysfunction of certain biological processes is implicated in different diseases in humans, including cardiovascular, cancer, or neurodegenerative disorders. Not only human cells and tissues are affected by ROS but also all other biological systems, including plants and microorganisms. Primary targets of ROS are proteins, lipids, and nucleic acids. Modifications of these macromolecules result mostly in the start of signalling cascades between proteins, proteins and DNA, DNA and RNA, proteins and RNA, proteins and lipids within single cell compartments, entire cells, or tissues. In this chapter, basics of tools of structural biology (i.e., X-ray crystallography, NMR, and EPR spectroscopy) as well as bioinformatics are presented. These tools are explained as well as how they can be applied in the analysis of ROS-mediated modifications within macromolecules and systems, and perspectives are discussed