Heme is a central molecule in the biology of life. Its unique chemical properties make it a versatile co-factor in many biological reactions. Heme is also an important source of iron for bacteria. In this regard, bacteria use surface proteins to import host heme and then break the heme ring to release the iron. This latter reaction is catalyzed by proteins termed heme degrading enzymes (HDEs). Because of their iron-liberating properties and the importance of iron in bacterial physiology, HDEs have emerged as critical during the infection of mammalian hosts. The sporulating bacterium B. anthracis is the causative agent of anthrax disease and a weapon of bioterrorism. This Gram-positive rod grows to extraordinary levels in vertebrate hosts and thus serves as a model for iron uptake. Previous work with this pathogen uncovered an elegant system of surface and secreted hemophores that import host heme. The biological consequences of heme import in terms of the lifecycle of this pathogen have not been determined. Preliminary data presented here suggests B. anthracis encodes three distinct HDEs, all of which break down heme. This finding raises the interesting question as to why B. anthracis would require three seemingly redundant HDEs. It is proposed here that each HDE may be important during different phases of a developing B. anthracis infection.
In Aim 1, an inhalational model of infection, the most serious clinical form, is used to determine the contribution of each HDE to anthrax disease.
In Aim 2, the functional role of each HDE is probed in three important host niches: protection from host killing by alveolar macrophages, the detoxification of excess heme, and the utilization of iron from host hemoglobin in blood. These studies will determine if HDEs are anti-anthrax targets and where in the bacillus infection cycle they function.

Public Health Relevance

The overall purpose of this study is to understand how B. anthracis, the cause of anthrax disease, is able to acquire critical nutrients during an infection. The work proposed here will lead to a functional understanding of the role of three key enzymes in this disease. This knowledge can be broadly applied to the study of related human pathogens.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21AI125778-01A1
Application #
9323699
Study Section
Special Emphasis Panel (ZRG1-IDM-B (80)S)
Program Officer
Mukhopadhyay, Suman
Project Start
2017-01-23
Project End
2018-12-31
Budget Start
2017-01-23
Budget End
2017-12-31
Support Year
1
Fiscal Year
2017
Total Cost
$237,750
Indirect Cost
$87,750
Name
Baylor College of Medicine
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
051113330
City
Houston
State
TX
Country
United States
Zip Code
77030