The Immune Inhibitor A1 Protease of <em>Bacillus Anthracis</em>

<p><em>Bacillus anthracis</em>, an organism ubiquitous in the soil and the causative agent of anthrax, utilizes multiple mechanisms to regulate secreted factors; one example is the activity of secreted proteases. One of the most abundant proteins in the culture supernates of <em>B. anthracis</em> is the Immune Inhibitor A1 (InhA1) protease. Here, I demonstrate that InhA1 modulates the abundance of approximately half of the proteins secreted into the culture supernates, including substrates that are known to contribute to the ability of the organism to cause virulence. For example, InhA1 cleaves the anthrax toxin proteins, PA, LF, and EF. InhA1 also targets a number of additional proteases, including Npr599, contributing to a complex proteolytic regulatory cascade with far-reaching affects on the secretome. Using an intra-tracheal mouse model of infection, I found that an <em>inhA</em>-null strain is attenuated in relation to the parent strain. The data indicate that reduced virulence of the <em>inhA</em> mutant strain may be the result of toxin protein deregulation, decreased association with macrophages, and/or the inability to degrade host antimicrobial peptides. </p> <p>Given the significant modulation of the secretome by InhA1, it is likely that expression of the protease is tightly regulated. To test this I examined <em>inhA1</em> transcript and protein levels in the parent and various isogenic mutant strains and found that InhA1 expression is regulated by several mechanisms. First, the steady state levels of <em>inhA1</em> transcript are controlled by the regulatory protein SinR, which inhibits <em>inhA1</em> expression. Second, InhA1 abundance is inversely proportional to the SinR-regulated protease camelysin, indicating the post-transcriptional regulation of InhA1 by camelysin. Third, InhA1 activity is dependent on a conserved zinc binding motif, suggesting that zinc availability regulates InhA1 activity. The convergence of these regulatory mechanisms signifies the importance of tight regulation of InhA1 activity, activity that substantially affects how <em>B. anthracis</em> interacts with its environment.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation (PhD)

Year dc:date.available

2010

Author dc:creator

• Pflughoeft, Kathryn

Contributors dc:contributor

• Theresa M. Koehler Ph.D.
• Jeffrey K. Actor Ph.D.
• David A. Engler, Ph.D.

• Bacillus anthracis
• secreted proteases
• proteases
• gene regulation
• post-translational regulation
• anthrax toxin proteins
• Microbiology

Repository record dc:identifier

https://digitalcommons.library.tmc.edu/utgsbs_dissertations/86

OAI identifier oai:identifier

oai:digitalcommons.library.tmc.edu:utgsbs_dissertations-1111