Titel: How to get rid of O2? Detoxification in Mycoplasma pneumoniae
Art: Abstractautor
Session: Workshop 01
Virulence Principles in Respiratory Tract Infections (FG MP)

Referent: Cedric Blötz (Göttingen)

Abstract - Text

As a human pathogen, Mycoplasma pneumoniae can cause severe illness. The close association with lung epithelial cells allows the organism to live with one of the smallest genomes (688 ORFs). This is reflected by a limited repertoire of enzymes, and by the reduced capabilities of the organisms" proteome. All life on earth is constantly exposed to reactive oxygen species (ROS). These compounds are highly reactive and can heavily damage macromolecules like DNA, proteins, and lipids. To minimize ROS induced damage, every cell needs to keep the balance between oxidants and antioxidants. Antioxidants can be enzymes like catalase, superoxide dismutase, and peroxiredoxins (Prx). Since M. pneumoniae lacks catalase and superoxide dismutase, this work was focused on the identification and characterization of Prx in M. pneumoniae. Prx are antioxidant enzymes, that degrade ROS via catalytic cysteine residues, and that are subsequently reduced via the thioredoxin system. Sequence alignments identified MPN625 and MPN668 as potential candidates. Both Prx candidates contain two conserved cysteine residues. In this work, their enzymatic activity against peroxides was demonstrated. The formation of homodimers is characteristic for Prx, and in this study it was shown, that MPN625 and MPN668 exist in this form. Furthermore, binding studies revealed two ligand binding sites of MPN625 and MPN668, which is consistent with homodimer formation. For the first time, clean deletions were performed and the genes encoding the Prx were successfully deleted from the genome of M. pneumoniae. This revealed no growth defect of the ∆prx single mutants in glucose and glycerol containing media, as well as no altered cytotoxicity against human bronchial epithelial cells (HBECs). However, the single mutants were less sensitive to peroxide stress than the WT. In agreement with expression studies, we suggest that MPN625 and MPN668 can take over the function of each other. Oxidative stress occurs, when the balance between ROS and antioxidants is shifted towards ROS. In this case, it is of major importance, that antioxidant enzymes are regulated in a way, that they can quickly respond to prevent oxidative stress. In this study, the trigger enzyme GlpQ and the regulator Spx were revealed to control expression of the two Prx. Thus, MPN625 and MPN668 are the functional Prx of the minimal bacterium M. pneumoniae. Accordingly, these antioxidant enzymes have been renamed PrxA (MPN625) and PrxB (MPN668).