Project B6

Ubiquitin-modifying enzymes of Simkania negevensis and their role in infection

Vera Kozjak-Pavlovic, Kay Hofmann

Simkania negevensis (Sne) is an obligate intracellular Chlamydia-like bacterium, connected to respiratory diseases in humans. Simkania spend most of their development cycle within intracellular vacuoles (SnCVs) and use a type III secretion system for injecting effectors into the host cell. Very few Sne effectors have been functionally characterized so far. A recently performed bioinformatical screen identified a surprisingly high number of putative ubiquitin-modifying enzymes, including no less than eleven deubiquitinase (DUB) candidates, which is in stark contrast to the 1-3 DUBs encoded by most other intracellular bacteria. Not only the number of Sne-encoded DUBs is remarkable, even more unusual is their great diversity, which includes two classes that have never before been found in bacteria. Besides DUBs, the Sne genome also encodes four putative ubiquitin ligases and two ubiquitin-like modifiers.

The major aim of this project is to identify the crucial factors and key substrates of Sne DUBs, as well as to elucidate their mode of action during infection. Candidate substrates will be identified by affinity purification and validated by proteomics, followed by studying the importance of selected DUB substrates for Sne biology. We also aim to identify cellular targets of the Sne-encoded ubiquitin ligases and to study their role in cell death regulation and defense evasion. Since our investigations would be greatly supported by the possibility to genetically modify Sne, we will try to adapt methods known to work on other environmental Chlamydia to S. negevensis.