CeBiTec Colloquium (unscheduled)

 date

Friday, January 4th 2013,17 c.t.

 location

G2-104, CeBiTec Building

 speaker

PD Dr. Haike Antelmann

Institut für Mikrobiologie
Ernst Moritz Arndt Universität Greifswald

title

Oxidative stress responses in Gram-positive bacteria and the role of the bacillithiol redox buffer

abstract Bacillus species utilize as thiol redox buffer bacillithiol (BSH) to maintain the redox balance. Under oxidative stress conditions, BSH reacts with protein thiols to form mixed BSH protein disulfides, termed as S-bacillithiolations. Protein S-bacillithiolation protects active site Cys residues against irreversible oxidation and functions as redox switch mechanism. Using redox proteomics and mass spectrometry, we identified eleven S-bacillithiolated proteins in B. subtilis after hypochlorite stress, including the OhrR repressor and the methionine synthase MetE. S-bacillithiolation inhibits MetE activity leading to methionine auxotrophy in NaOCl-treated cells. The redox-sensing OhrR repressor is inactivated by S-bacillithiolation after NaOCl stress resulting in up-regulation of the OhrA peroxiredoxin that confers NaOCl resistance. S-bacillithiolation is also wide-spread among other Firmicutes with 8 conserved and 29 unique S-bacillithiolated proteins identified in B. subtilis, Bacillus amyloliquefaciens, Bacillus pumilus, Bacillus megaterium and Staphylococcus carnosus. The S-bacillithiolome contains mainly biosynthetic enzymes for amino acids, cofactors, nucleotides; as well as translation factors, chaperones, redox and antioxidant proteins. S-bacillithiolation is accompanied by an increased BSSB level and a decreased BSH/BSSB redox ratio.

Besides the OhrR repressor, we identified the MarR/DUF24-type transcriptional regulator YybR (HypR) as hypochlorite-specific redox sensor that controls positively the nitroreductase YfkO (HypO). HypR resembles a 2-Cys-type regulator that is activated by Cys14-Cys49' intersubunit disulfide formation. The crystal structures of reduced and oxidized HypR proteins were resolved revealing structural changes upon HypR oxidation. In summary, B. subtilis uses the one-Cys-type OhrR repressor and the two-Cys-type HypR regulator as specific redox sensors for NaOCl stress. In addition, the BSH redox buffer plays an important role in redox control and protein protection against irreversible oxidation by S-bacillithiolations in Firmicutes bacteria.
 host

Dr. Jörn Kalinowski