ATP-dependent Mur ligases in Mycobacterium tuberculosis: search for potential therapeutic targets against Tuberculosis.
Lead Research Organisation:
Birkbeck, University of London
Department Name: Biological Sciences
Abstract
Tuberculosis (TB) a contagious disease caused by the ?Superbug? Mycobacterium tuberculosis, remains the leading cause of death worldwide.
Despite the presence of chemotherapy, extensive rise in antibiotic resistance is a cause of concern around the world, including the UK. In a reported case of extreme drug resistance (XDR) there is no new drug available that can combat the disease. Hence there is an urgent need for new drug development.
A key feature of Mycobacterium tuberculosis is the unique cell wall of consisting of three major layers - peptidoglycan, arabinogalactan and mycolic acid covalently linked. The cell wall architecture and presence of ?peptidoglycans?, not only helps in maintaining the shape and size of the bacterial cell, but also protects the bacteria from toxic radicals, osmotic lysis, and foreign attack.
Thus the crucial nature of the protective cell wall-peptidoglycan in M. tuberculosis should be exploited for new drug discovery against TB. Characterisation of the peptidoglycan biosynthesis will help in identification of potential targets for new drugs.
The proposed study aims to identify those cellular components (enzymes) that are vital to the production of this protective cell wall, and thus essential for the survival of the TB-bacteria. We will be investigating, in detail, the structural and functional dynamics of the enzymes that play major roles in the peptidoglycan biosynthesis. In addition, we will also modify these vitally important TB enzymes and observe how the TB-Superbugs survive.
Despite the presence of chemotherapy, extensive rise in antibiotic resistance is a cause of concern around the world, including the UK. In a reported case of extreme drug resistance (XDR) there is no new drug available that can combat the disease. Hence there is an urgent need for new drug development.
A key feature of Mycobacterium tuberculosis is the unique cell wall of consisting of three major layers - peptidoglycan, arabinogalactan and mycolic acid covalently linked. The cell wall architecture and presence of ?peptidoglycans?, not only helps in maintaining the shape and size of the bacterial cell, but also protects the bacteria from toxic radicals, osmotic lysis, and foreign attack.
Thus the crucial nature of the protective cell wall-peptidoglycan in M. tuberculosis should be exploited for new drug discovery against TB. Characterisation of the peptidoglycan biosynthesis will help in identification of potential targets for new drugs.
The proposed study aims to identify those cellular components (enzymes) that are vital to the production of this protective cell wall, and thus essential for the survival of the TB-bacteria. We will be investigating, in detail, the structural and functional dynamics of the enzymes that play major roles in the peptidoglycan biosynthesis. In addition, we will also modify these vitally important TB enzymes and observe how the TB-Superbugs survive.
Technical Summary
The recurrence of Tuberculosis (TB) as a global health emergency has highlighted the urgent need for new therapeutic targets to facilitate the development of new drugs against the disease. TB is caused by the micro-organism Mycobacterium tuberculosis which is a member of the order Actinomycetales. A key common feature of this order is their complex cell walls, which consist of an unusual mycolyl-arabinogalactan-peptidoglycan (mAGP) complex. Within the cell wall, peptidoglycan not only provides shape and structural integrity to the bacterial cell, but also plays a critical role in protecting the bacteria against osmotic lysis and hydrolytic enzymes produced by host defence mechanisms. Mycobacterium tuberculosis is unique in its peptidoglycan architecture indicating that the enzymes regulating the synthesis of the pivotal substrates are novel therapeutic targets.
UDP-N-acetylmuramoyl-tripeptide ligase (MurE) is a member of the ATP-dependent ligase family and incorporates different amino acids including meso-diaminopimelate into peptidoglycan during synthesis in a species-specific manner. In addition, MurF acts at the final stage of UDP sugar linked polypeptide synthesis. The product of this reaction, UDP N-acetyl muramoyl pentapeptide, is the key substrate for the membrane bound transition stage of peptidoglycan biosynthesis. Due to the multi-facetted nature of the functional implications of ATP-dependent ligases, it provides a possible vulnerability that can be exploited. MurE and MurF are coded for in the M. tuberculosis genome by a single copy of the gene. This decreases the possibility that any disruption of the MurE and/or MurF protein will be compensated for by an alternative biochemical pathway. Moreover, these enzymes do not have human homologues. The combinations of these features make ATP-dependent ligases excellent candidates for the identification of novel therapeutic drug targets.
These two biochemical steps are pivotal for endogenous peptidoglycan biosynthesis pathways. Our knowledge is limited in these central biochemical reactions of Mycobacterium tuberculosis, the enzymes involved in these reaction steps and their regulation, on the cell function and physiology of the unique genus. We propose to elucidate the structure and function of the enzymes involved in the series of functionally linked ATP dependant ligation reactions in Mycobacterium tuberculosis, which are potential drug targets for combating TB.
UDP-N-acetylmuramoyl-tripeptide ligase (MurE) is a member of the ATP-dependent ligase family and incorporates different amino acids including meso-diaminopimelate into peptidoglycan during synthesis in a species-specific manner. In addition, MurF acts at the final stage of UDP sugar linked polypeptide synthesis. The product of this reaction, UDP N-acetyl muramoyl pentapeptide, is the key substrate for the membrane bound transition stage of peptidoglycan biosynthesis. Due to the multi-facetted nature of the functional implications of ATP-dependent ligases, it provides a possible vulnerability that can be exploited. MurE and MurF are coded for in the M. tuberculosis genome by a single copy of the gene. This decreases the possibility that any disruption of the MurE and/or MurF protein will be compensated for by an alternative biochemical pathway. Moreover, these enzymes do not have human homologues. The combinations of these features make ATP-dependent ligases excellent candidates for the identification of novel therapeutic drug targets.
These two biochemical steps are pivotal for endogenous peptidoglycan biosynthesis pathways. Our knowledge is limited in these central biochemical reactions of Mycobacterium tuberculosis, the enzymes involved in these reaction steps and their regulation, on the cell function and physiology of the unique genus. We propose to elucidate the structure and function of the enzymes involved in the series of functionally linked ATP dependant ligation reactions in Mycobacterium tuberculosis, which are potential drug targets for combating TB.
