Abstract
Bacteria are permanently in contact with reactive oxygen species (ROS), both over the course of their life cycle as well that present in their environment. These species cause damage to proteins, lipids, and nucleotides, negatively impacting the organism. To detect these ROS molecules and to stimulate the expression of proteins involved in antioxidative stress response, bacteria use a number of different protein-based regulatory and sensory systems. ROS-based stress detection mechanisms induce posttranslational modifications, resulting in overall conformational and structural changes within sensory proteins. The subsequent structural rearrangements result in changes of protein activity, which lead to regulated and appropriate response on the transcriptional level. Many bacterial enzymes and regulatory proteins possess a conserved signature, the zinc-containing redox centre Cys-X-X-Cys in which a disulfide bridge is formed upon oxidative stress. Other metal-dependent oxidative modifications of amino acid side-chains (dityrosines, 2-oxo-histidines, or carbonylation) also modulate the activity of redox-sensitive proteins. Using molecular biology, biochemistry, biophysical, and structure biology tools, molecular mechanisms involved in sensing and response to oxidative stress have been elucidated in detail. In this review, we analyze some examples of bacterial redox-sensing proteins involved in antioxidative stress response and focus further on the currently known molecular mechanism of function.
Highlights
Interference in the balance between the environmental production of reactive oxygen species (ROS), including hydroxyl radicals (OH) and hydrogen peroxide (H2O2), and the ability of biological systems to readily detect and detoxify them, or repair the resulting damage, are defined as oxidative stress
We will focus on intramolecular disulfides that are formed within Cysteine residues (Cys)-X-X-Cys motifs—(X: any amino acid)—a motif that is widespread in bacterial sensor proteins (Table 1)
ROS may be considered to be beneficial compounds, as they function as signalling molecules that lead to a coordinated response of bacteria under redox-stress conditions
Summary
Interference in the balance between the environmental production of reactive oxygen species (ROS), including hydroxyl radicals (OH) and hydrogen peroxide (H2O2), and the ability of biological systems to readily detect and detoxify them, or repair the resulting damage, are defined as oxidative stress. To reduce the hazardous effects of iron-based production of OH, bacteria produce proteins with an enzymatic activity to degrade ROS (i.e., superoxide dismutases, catalases, peroxidases, and alkylhydroperoxide reductases), other small redox proteins (thioredoxins and glutaredoxins) as well as low molecular-weight thiols (glutathione and mycothiol) [8, 9]. All these cell components contribute in maintaining a reducing environment both in the cell and in controlling the extent of the oxidative burst. We will give an overview of them and focus further on signalling pathways in which redox-active cysteines as well as iron ions are involved
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