Mechanistic Investigation of Unnatural Substrates for Enzymatic Production of Hydrogen sulfide in Bacteria

Abstract

The mode of action of antibiotics is under investigation pertaining to the role of reactive oxygen species (ROS) that are thought to be generated as a downstream consequence of the antibiotic assault on its primary targets. Many studies have shown that hydrogen sulfide (H2S) production in bacteria is, in some way, upregulated in periods of such oxidative stress. Since H2S is known to act as an antioxidant, it serves to abate the deleterious effects of antibiotics on bacteria, conferring on it what we know, and call, as antibiotic resistance.

The question being investigated in this study is the extent to which H2S provides protection to bacteria against antibiotics – i.e. if the intrinsic levels of H2S in bacteria are changed, will it translate to changes observed in their resistance to antibiotics?

Taking Escherichia coli as the model, we cloned, overexpressed, and purified the only known enzyme, 3-Mercaptopyruvate sulfurtransferase (Ec3-MST) that produces H2S in it. This study then takes up the systematic development of novel substrates for Ec3-MST that have been shown to produce H2S at different rates in vitro. The mechanism of turnover of these substrates is then elucidated step by step.

The study leaves us with the prospect of testing these unnatural substrates on E. coli to observe if the varied levels of H2S can be obtained in vivo as well. By coincubating the bacteria with different antibiotics, this model can then be used to address our original question as to what extent is H2S able to protect bacteria from antibiotic stress, and more importantly, bring in a more complete understanding as to how antibiotics actually work.