Characterization of hypochlorous acid as potent physiological antimicrobial
Biochemistry
Metabolism, Biochemistry and Genetics of Microorganisms
Final Report Abstract
Accumulation of reactive oxygen and chlorine species (RO/CS) is generally regarded to be a toxic and highly undesirable event, which serves as contributing factor in aging and many age-related diseases. However, oxidative stress is not always a bad thing; in fact, production of high levels of hypohalous acids (HOX) plays an important physiological role in the innate immune response, where it provides a powerful strategy for killing invading pathogens and controlling bacterial colonization. Biochemical and cell biological studies of how bacteria and other microorganisms deal with HOX have now provided important new insights into the physiological consequences of oxidative stress, the major targets that need protection, and the cellular strategies employed by organisms to mitigate the damage. While transcriptional stress responses are typically highly effective in dealing with stress-related cell damage, the gap between the time the stress is initially sensed and the moment defense and repair proteins are functional can be a life-threatening issue, especially when bacteria experience fast acting stressors, such as oxidative stress. Therefore, it is not surprising that microbes have developed posttranslational mechanisms that allow a more rapid response towards these stress conditions. One of the most efficient posttranslational stress response systems that bacteria employ to defend themselves against deleterious oxidative stress conditions, is the conversion of ATP into the highly conserved, universal prebiotic polymer polyphosphate (polyP), which consists of long chains of up to 1000 phosphoanhydride bond-linked phosphates. Pathogens that lack the ability to produce polyP suffer from a number of different phenotypes, including increased sensitivity towards oxidative stress and reduced formation of antibiotic-resistant biofilms, which greatly affects their virulence. We therefore screened for potential inhibitors that would affect polyP homeostasis, and identified mesalamine, a drug that serves as gold standard in treating ulcerative colitis, an inflammatory bowel disease characterized by chronic inflammation and affecting 1.6 million people in the US. In this project, I found that mesalamine treatment rapidly decreases polyP levels in a wide variety of different bacteria, ranging from clinically isolated uropathogenic E. coli and P. aeruginosa strains to members of the human gut microbiota. By decreasing the polyP levels in the cell, mesalamine mimics the phenotypes reported for cells lacking the ability to produce polyP, because the drug (i) increased the sensitivity to inflammatory oxidants such as hypochlorous acid, that are produced to combat harmful bacteria (ii) reduced biofilm formation and (iii) antibiotic resistant persister cell formation, as well as (iv) significantly impaired the ability to colonize a host. We gave mesalamine to a group of healthy study participants and took samples from the participant's gastrointestinal tract. We observed that the moment we could detect mesalamine, the polyP levels dropped dramatically, suggesting that mesalamine affects microbes by targeting polyP homeostasis. In a second project, I characterized the three physiologically relevant forms of HOX, namely hypochlorous acid (HOCl), hypobromous acid (HOBr), and hypothiocyanous acid (HOSCN). I found that that HOSCN is a highly proteotoxic oxidant and identified polyP as a general response system that bacteria employ to defend themselves against severe oxidative stress conditions. PolyP appears to be particularly well suited to protect PA14 against HOSCN-mediated protein damage.
Publications
- (2015) "Protein quality control under oxidative stress conditions" J Mol Bio 427:1549-63
Dahl JU, Gray MJ, Jakob U
(See online at https://dx.doi.org/10.1016fj.jmb.2015.02.014) - "Polyphosphate - An Ancient Modifier of Amyloidogenic Processes" Mol Cell 63:768-780
Cremers CM, Knoefler D, Gates S, Martin N, Dahl JU, Xie L, Chapman MW, Galvan V, Southworth DR, Jakob U
(See online at https://dx.doi.org/10.1016fj.molcel.2016.07.016) - "The anti-inflammatory drug mesalamine inhibits bacterial polyphosphate accumulation" Nature Microbiology 2, 16267
Dahl JU, Gray MJ, Bazopoulou D, Beaufay F, Lempart J, Koenigsknecht MJ, Wang Y, Baker JR, Hasler WL, Young VB, Sun D, Jakob U
(See online at https://doi.org/10.1038/nmicrobiol.2016.267) - (2016) "Detection of the pH-dependent activity of Escherichia coli chaperone HdeB in vitro and in vivo" J Vis Exp, (116)
Dahl JU, Koldewey P, Bardwell J, Jakob U
(See online at https://doi.org/10.3791/54527)
