Thesis (MScMedSc)--Stellenbosch University, 2012. / Bibliography / ENGLISH ABSTRACT: Evidence suggests that biological mechanisms, such as energy dependant efflux pumps, in addition to the rpoB gene mutations, define the level of rifampicin (RIF) resistance in drug resistant Mycobacterium tuberculosis (M. tuberculosis) strains with similar genetic backgrounds. Additionally, proteomic studies showed up-regulation of components of F1F0-ATP synthase enzyme, encoded by the atpBEFHAGDC operon which is responsible for ATP production, in response to RIF. The hypothesis of the current study is that the exposure of a multi-drug resistant (MDR) M. tuberculosis strain to RIF leads to the initiation of a signalling cascade of events. This results in the increased expression of F1F0-ATP synthase leading to an increase in energy production and subsequent activation of efflux pumps. RIF will thus be actively extruded from the cell, increasing the level of RIF resistance. This study aims to identify genetic regions responsible for the regulation of expression of the atpBEFHAGDC operon. Additionally we aim to identify other novel mechanisms contributing to the level of RIF resistance in M. tuberculosis. A specialised reporter vector was constructed to monitor the expression of atpBEFHAGDC, with the use of a fluorescent protein. Subsequently a library of random knockouts was created by transposon mutagenesis in order to identify possible regulators, as well as novel mechanisms contributing to RIF resistance.
Two hypothetical proteins, Rv2005c and Rv2417c, were identified in M. tuberculosis transposon mutants showing decreased fluorescence correlating to decreased expression of atpBEFHAGDC. Rv2005c encodes a universal stress protein, suggesting its potential role in a signalling cascade initiated upon RIF exposure. In a model pathway of regulation we propose that the product of Rv2005c is responsible for releasing a repressor protein, Rv1049, thereby stimulating a cascade of signalling events resulting in the up-regulation of atpBEFHAGDC. This increase in ATP production thereby fuels the extrusion of RIF from the cell via efflux pumps. In addition, it was found that disruptions in Rv2524c (fatty acid synthase), Rv1048c (hypothetical protein) and Rv3163c (probable conserved secreted protein) resulted in an increase in the level of RIF resistance in a RIF resistant clinical isolate. Interestingly, Rv2524c also showed to have a potential role in regulation of atpBEFHAGDC, whereby it ensures the repression of atpBEFHAGDC. Another gene identified to be involved in the increase in RIF resistance, Rv0260c, is annotated as a possible transcriptional regulator. This study was successful in identifying possible regulatory proteins involved in regulation of the F1F0-ATP synthase in response to RIF, and highlights the complexity of the regulatory events that occur in response to RIF in a MDR M. tuberculosis strain. This study was also successful in identifying candidates for functional analysis to determine novel mechanisms contributing to the level of RIF resistance in M. tuberculosis. Together these findings demonstrate that RIF resistance in M. tuberculosis is more complex than originally thought. Considering that anti-Tuberculosis (TB) drug TMC207 targets the F1F0-ATP synthase, a key enzyme in the production of energy in mycobacteria, the newly identified regulatory genes of F1F0-ATP synthase may represent ideal targets for novel anti-TB drug design. / AFRIKAANSE OPSOMMING: Huidige dogma toon dat mutasies in die rpoB geen vir rifampicin (RIF) weerstandigheid in Mycobacterium tuberculosis (M. tuberculosis) verantwoordelik is. Onlangs is egter bevind dat ander biologiese meganismes, soos energie afhanklike membraanpompe, saam met mutasies in hierdie geen, die verskillende vlakke van RIF weerstandigheid in M. tuberculosis isolate met soortgelyke genetiese agtergrond kan verklaar. Addisionele proteïen studies het gewys dat die komponente van die F1F0-ATP sintase ensiem, wat verantwoordelik vir ATP sintese is en gekodeer word deur die atpBEFHAGDC operon, opgereguleer word na RIF blootstelling. Die hipotese van hierdie studie is dat blootstelling van ‘n multi-middelweerstandige M. tuberculosis isolaat aan RIF aanleiding sal gee tot ʼn aanvanklike sein wat dan verskeie ander biologiese paaie sal aanskakel. Hierdie gebeure sal dan lei tot ‘n verhoging in geenuitdrukking van die F1F0-ATP sintase operon met gevolglike verhoging in energie produksie, wat uiteindelik energie afhanklike membraan pompe sal aanskakel. Die aktiewe uitpomp van RIF uit die sel sal dan ʼn verhoging in die vlak van RIF weerstandigheid veroorsaak. Die eerste doel van hierdie studie is om genetiese areas te identifiseer wat verantwoordelik is vir die regulering van geenuitdrukking van die atpBEFHAGDC operon. Die tweede doel is om nuwe meganismes te identifiseer wat verskille in die vlakke van RIF weerstandigheid in verskillende nou verwante kliniese isolate sal verklaar. ʼn Gespesialiseerde vektor wat die geenuitdrukking van die atpBEFHAGDC operon sal monitor is suksesvol ontwikkel met die gebruik van ʼn fluoresserende proteïen. Daarna is van die transposon mutagenese metode gebruik gemaak om ʼn biblioteek van ewekansige geenuitlatings te maak en hierdie biblioteek is dan gebruik om nuwe meganismes van RIF weerstandigheid te ondersoek. Hierdie studie het twee hipotetiese proteïene, Rv2005c en Rv2417c, in M. tuberculosis transposon mutante geïdentifiseer wat verantwoordelik is vir verlaagde fluoressensie. Dit korreleer met die verwagte verlaagde geenuitdrukking van atpBEFHAGDC. Die geen Rv2005c kodeer vir ʼn universele spanningsproteïen en die resultaat voorspel dat Rv2005c ʼn potensiële rol het om ʼn netwerk van seine in die bakterium aan te skakel direk na blootstelling aan RIF. In ʼn voorgestelde model van regulerende paaie voorspel ons dat die produk van Rv2005c verantwoordelik is vir die vrystelling van ʼn onderdrukker proteïen, Rv1049. Dit lei dan tot die stimulering van ʼn netwerk van intrasellulêre seine wat aanleiding gee tot die opregulering van atpBEFHAFDC. Die opregulering van atpBEFHAFDC sal dan aanleiding gee tot ʼn verhoging in ATP produksie wat die uitpomp van RIF uit die sel sal versnel met die gebruik van energie afhanklike membraan pompe. Dit is verder gevind dat uitskakeling van die gene Rv2524c (vetsuur sintase), Rv1048c (hipotetiese proteïen) en Rv3163c (moontlike konserwatiewe uitskei proteïen) aanleiding gegee het tot die verhoging in die vlakke van RIF weerstandigheid in ʼn RIF weerstandige kliniese isolaat. In die studie is ook bewys dat Rv2524c ʼn potensiële rol in die regulering van atpBEFHAGDC het deurdat dit die onderdrukking van atpBEFHAGDC verseker. Rv0260c is voorheen gelys as ʼn moontlike transkripsionele reguleerder wat betrokke is by die verhoging van RIF weerstandigheid.
Hierdie studie was suksesvol in die identifisering van moontlike gene en proteïne wat betrokke is in die regulering van die F1F0-ATP sintase in reaksie tot RIF blootstelling. Dit beklemtoon die kompleksiteit van die regulerende gebeurtenisse wat plaasvind in reaksie tot RIF blootstelling in ʼn multi-middelweerstandige M. tuberculosis isolaat. Verder was daar suksesvol kandidaat gene en ʼn reguleerder geïdentifiseer wat in toekomstige studies ondersoek kan word vir hulle funksionele bydrae om nuwe meganismes te vind wat die varierende vlakke van RIF weerstandigheid in M. tuberculosis sal verklaar. Opsommend demonstreer hierdie studie dat RIF weerstandigheid meer kompleks is as wat voorheen aangeneem was. Die nuwe baie belowende teen-Tuberkulose middel, TMC207, se aanslag is gemik op die belangrike ensiem (F1F0-ATP sintase) wat in hierdie studie ondersoek was. Dus kan nuut geïdentifiseerde proteïene wat betrokke is by die regulering van hierdie ensiem beskou word as ideale kandidate vir die ontwikkeling van nuwe teen -Tuberkulosemiddels. / The National Research Foundation and the Department of Biomedical Sciences
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20386 |
| Date | 03 1900 |
| Creators | Black, Philippa |
| Contributors | Warren, R. W., Louw, G. E., Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xvii, 100 p. : col. ill. |
| Rights | Stellenbosch University |
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