Cytochrome bd-I in Escherichia coli is less sensitive than cytochromes bd-II or bo′' to inhibition by the carbon monoxide-releasing molecule, CORM-3: N-acetylcysteine reduces CO-RM uptake and inhibition of respiration

• Published in: Biochimica et biophysica acta 2013-09, Vol.1834 (9), p.1693-1703
• Main Authors: Jesse, Helen E, Nye, Tacita L, McLean, Samantha, Green, Jeffrey, Mann, Brian E, Poole, Robert K
• Format: Article
• Language: English
• Subjects: acetylcysteine; Acetylcysteine - pharmacology; anti-infective agents; antioxidant activity; Antioxidants - pharmacology; bacteria; carbon; Carbon Monoxide - metabolism; Cell Membrane - drug effects; Cell Membrane - metabolism; Cell Respiration - drug effects; cytochromes; Cytochromes - antagonists & inhibitors; Cytochromes - metabolism; Electron Transport Chain Complex Proteins - antagonists & inhibitors; Electron Transport Chain Complex Proteins - metabolism; Escherichia coli; Escherichia coli - metabolism; Escherichia coli Proteins - antagonists & inhibitors; Escherichia coli Proteins - metabolism; Heme - metabolism; Hyperbaric Oxygenation; Leghemoglobin - metabolism; mammals; mechanism of action; Organometallic Compounds - pharmacology; Oxidoreductases - antagonists & inhibitors; Oxidoreductases - metabolism; oxygen; Oxygen Consumption - drug effects; Ruthenium - pharmacology; thiols; toxicity; viability
• ISSN: 1570-9639; 0006-3002; 1878-1454
• DOI: 10.1016/j.bbapap.2013.04.019

Background: CO-releasing molecules (CO-RMs) are potential therapeutic agents, able to deliver CO – a critical gasotransmitter – in biological environments. CO-RMs are also effective antimicrobial agents; although the mechanisms of action are poorly defined, haem-containing terminal oxidases are primary targets. Nevertheless, it is clear from several studies that the effects of CO-RMs on biological systems are frequently not adequately explained by the release of CO: CO-RMs are generally more potent inhibitors than is CO gas and other effects of the molecules are evident. Methods: Because sensitivity to CO-RMs cannot be predicted by sensitivity to CO gas, we assess the differential susceptibilities of strains, each expressing only one of the three terminal oxidases of E. coli — cytochrome bd-I, cytochrome bd-II and cytochrome bo′, to inhibition by CORM-3. We present the first sensitive measurement of the oxygen affinity of cytochrome bd-II (Kₘ 0.24μM) employing globin deoxygenation. Finally, we investigate the way(s) in which thiol compounds abolish the inhibitory effects of CORM-2 and CORM-3 on respiration, growth and viability, a phenomenon that is well documented, but poorly understood. Results: We show that a strain expressing cytochrome bd-I as the sole oxidase is least susceptible to inhibition by CORM-3 in its growth and respiration of both intact cells and membranes. Growth studies show that cytochrome bd-II has similar CORM-3 sensitivity to cytochrome bo′. Cytochromes bo′ and bd-II also have considerably lower affinities for oxygen than bd-I. We show that the ability of N-acetylcysteine to abrogate the toxic effects of CO-RMs is not attributable to its antioxidant effects, or prevention of CO targeting to the oxidases, but may be largely due to the inhibition of CO-RM uptake by bacterial cells. Conclusions: A strain expressing cytochrome bd-I as the sole terminal oxidase is least susceptible to inhibition by CORM-3. N-acetylcysteine is a potent inhibitor of CO-RM uptake by E. coli. General significance: Rational design and exploitation of CO-RMs require a fundamental understanding of their activity. CO and CO-RMs have multifaceted effects on mammalian and microbial cells; here we show that the quinol oxidases of E. coli are differentially sensitive to CORM-3. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.