Influence of the substrate specificity of Mycobacterium tuberculosis ClpX on the transcriptional profile

Abstract

Cellular homeostasis in bacteria is maintained by diverse molecular machines. These include several one-component systems (OCS), two- component systems (TCS), chaperone proteins, proteases, proteolytic complexes and transcription factors that regulate protein synthesis and recycling. Protein and oligonucleotide recycling provides a route to clear the cell of aggregated and non-functional bio-molecules thereby mitigating metabolic stress and ensuring bacterial survival. Protein recycling machines in bacteria have been examined in different contexts. These include proteases that function in isolation and chaperone assisted proteases for degradation of specific bio-molecules. The focus of the work reported in this thesis was to understand the mechanism by which proteolytic assemblies influence intracellular signal transduction. This aspect is of particular relevance for the human pathogen Mycobacterium tuberculosis due to its growth features, ability to endure diverse micro-environments inside the host and a pronounced latent phase prior to onset of disease. M. tuberculosis has several proteases that include FtsH (involved in cell division), Clp proteases- ClpX, ClpC1, ClpP1 and ClpP2 (involved in the maintenance of cellular homeostasis) and the proteasome. Unlike Escherichia coli and Bacillus subtilis, there are no homologues of Lon and HslUV proteases in M. tuberculosis. Indeed, all the Clp proteases in M. tuberculosis are essential. The work described in this thesis reveals the basis by which substrate selectivity is enforced by these chaperone-proteases with direct and indirect repercussions on bacterial adaptation and cellular changes. These studies suggest a link between protein recycling mechanisms and the transcription process suggesting feed-forward and feed-back loops that ensure cellular homeostasis and adaptation to diverse stresses