Newer Insights On Structure, Function And Regulation Of Dps Protein From Mycobacterium smegmatis
Chowdhury, Rakhi Pait
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The first chapter will provide an introduction to the physiology, pathogenesis and biology of mycobacteria. Host-pathogen interactions, different modes of resistance of the bacteria, adaptations for survival under nutrient and oxygen depleted conditions has been discussed. This is followed by a general discussion on gene expression and regulation in the microbe. The physiology of bacteria under stresses from the view of the transcriptional regulation of specific genes has also been discussed. The scope and objective of the present study in M. smegmatis covered in the thesis has been considered at the end. The next chapter discusses the characterization of msdps promoter in vivo with the help of reporter gene assay technologies. With the advent of promoterless E. coli-mycobacterium shuttle vectors, activity assays can be easily performed to characterize unknown upstream putative promoter sequences of genes. Both the 1 kb upstream as well as a 200bp upstream region of msdps gene has been characterized by. Primer extension analysis and subsequent site directed mutagenesis studies reveal +1 transcription start site and the promoter consensus sequence for the msdps gene respectively. Next chapter comprises of the method of constructing heterologous in vitro transcription machinery in mycobacteria. It is followed by characterization of transcription initiation at two dps promoters of M. smegmatis. A novel pull-down assay has been designed which enabled us to identify the sigma factors in the reconstituted RNA polymerases to be associated with the respective dps promoters and to compare the regulation of the two genes at transcription level. Further characterization through single round in vitro transcription at mycobacterial promoters has been attempted. The following two chapters provide some newer insights into the structure-function relationship of the first Dps molecule, MsDps (MsDps1) with respect to its DNA binding activity. The DNA binding activity is associated with the higher oligomeric form only. With the help of time resolved anisotropy and Förster Resonance Energy Transfer (FRET) experiments, we have monitored the nature of Dps dodecamer-DNA complex and mapped the distance between the N and C169 position in the absence and the presence of DNA. A new computational programme, Maximum Entropy Method (MEM) has been applied successfully to analyze data obtained from phase-modulation (Phi-M) lifetime experiments in order to get distribution of lifetime. In the last chapter a new method is adopted to predict amino acids important for stabilizing the interface in a trimeric structure. Subsequently, single and double amino acid mutants of the native MsDps protein has been constructed through site directed mutagenesis and are scored for the ability of the mutants to oligomerize under conditions similar to that of the native protein. This helped us to propose a hypothetical model of the overall mechanism of the protein oligomerization process in solution.