ROS Defense Systems and Terminal Oxidases in Bacteria

Abstract

Reactive oxygen species (ROS) comprise the superoxide anion (O2·−), hydrogen peroxide (H2O2), hydroxyl radical (·OH), and singlet oxygen (1O2). ROS can damage a variety of macromolecules, including DNA, RNA, proteins, and lipids, and compromise cell viability. To prevent or reduce ROS-induced oxidative stress, bacteria utilize different ROS defense mechanisms, of which ROS scavenging enzymes, such as superoxide dismutases, catalases, and peroxidases, are the best characterized. Recently, evidence has been accumulating that some of the terminal oxidases in bacterial respiratory chains may also play a protective role against ROS. The present review covers this role of terminal oxidases in light of recent findings.

Impact of Hydrogen Sulfide on Mitochondrial and Bacterial Bioenergetics

“…It is suggested that H 2 S prevents oxidative DNA damage in bacteria via the following cytoprotective mechanisms: (i) direct reduction of H 2 O 2 into H 2 O; (ii) depletion of Fe 2+ , a catalyst of the Fenton reaction; (iii) transient depletion of free cysteine, a reducing agent that fuels the Fenton reaction; and (iv) stimulation of the activities of superoxide dismutase (SOD) and catalase [ 15 ]. The latter two enzymes are the well-known ROS scavenging systems [ 16 ]. It should be noted, however, that Shatalin et al [ 15 ] did not suggest a mechanism for the depletion of Fe 2+ and free cysteine by H 2 S.…”

Proton Pumping and Non-Pumping Terminal Respiratory Oxidases: Active Sites Intermediates of These Molecular Machines and Their Derivatives

“…HCOs catalyze the transfer of electrons from quinols or cytochromes to oxygen with the formation of water coupled to the generation of proton motive force [ 2 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. In contrast to bd -type oxidases, HCOs generate the proton motive force not only by the transfer of electrons and protons to the catalytic center from different sides of the membrane but also due to the unique ability for redox-coupled directed proton pumping through the membrane [ 23 ].…”

“…Members of the other two families use cytochrome c and possibly another electron donor different than quinol [ 4 ]. Notwithstanding, to date all the biochemically characterized bd -type cytochromes appeared to be quinol oxidases [ 14 , 78 , 79 , 80 ]. Further research is required to obtain and characterize a bd enzyme that would use an electron donor other than quinol.…”

“…Based on general considerations, the organization of the proton-conducting input pathways in bd -type oxidases should be simpler since the major function of the A family HCOs is a generation of the proton motive force whereas the bd enzymes do not pump additional protons across the membrane. Instead, cytochromes bd play essential roles in bacterial physiology and pathogenesis [ 14 , 80 , 84 , 85 , 86 , 87 , 88 ]. The mechanism of transfer of pumped protons along the same pathway (at least a significant part of it) as is used for the transfer of substrate protons (D channel in the A family oxidases; K channel in oxidases of the B and C families) requires a special device to prevent access of pumped protons to the oxygen-reductase center.…”

“…In accordance with the important physiological role of the bd -type oxidases, there is accumulating evidence that cytochromes bd make bacteria resistant to nitric oxide (NO) [ 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 ], peroxynitrite [ 85 , 103 ], H 2 O 2 [ 14 , 104 , 105 , 106 , 107 ], cyanide [ 108 , 109 , 110 ], sulfide [ 110 , 111 , 112 , 113 ], and ammonia [ 114 ]. The ability of the bd oxidases to degrade these hazardous compounds is provided not only by the efficiency of their binding to the reaction center and the transfer of electrons to it, but also by the supply of protons through the proton-conducting input pathways.…”