No description available.

No description available.

No description available.

No description available.

An investigation of amino acid metabolism in Streptomyces coelicolor, including the anabolism of tryptophan, histidine, the branched-chain amino acids and proline, as well as the catabolism of the latter, is reported. The experiments reported herein were conceptually conceived within a functional genomics framework. For this purpose the complete genome sequence of S. coelicolor was systematically exploited. Moreover, the current knowledge on the physiology of Streptomyces was taken onboard, as well as the prevailing and emerging notions on the evolution of proteins and metabolic pathways. Some of the results obtained using S. coelicolor as a model organism were expanded to other actinomycetes, such as Mycobacterium tuberculosis. This was aided by a comparative genomics analysis of the actinomycetes whose genomes have been sequenced. The theoretical principles that give support to this thesis are introduced in Chapter 1. This study was greatly facilitated by the development of a novel PCRtargeting mutagenesis method of which details can be found in Chapter VII. The discovery of a common isomerase for tryptophan and histidine biosynthesis is reported in Chapter II. This discovery arose from efforts aimed at reconstructing the tryptophan biosynthetic pathway of S. coelicolor, since the genome sequence project of this organism failed to identifiy a trpF gene coding for the enzyme phosphoribosyl anthranilate isomerase. The solution of this functional genomics discrepancy led to the discovery of a putative (~a)8-barrel enzyme, termed PriA, whose preliminary functional and structural characterisation is reported in Chapter III. The evolutionary implications of the discovery of PriA are discussed within Chapters III and N. A comparative genomics analysis of actinomycetes centred on the priA gene is presented in the latter Chapter, supporting the notion that this novel protein is spread across the high (0 + C) content Gram-positive organisms. Indeed, it was predicted that a priA orthologue accounts for the lack of a trpF gene from the genome of M tuberculosis, a hypothesis that proved to be correct. Finally, evidence to support the notion that the histidine and tryptophan biosynthetic pathways co-evolved is presented. In contrast to the isomerisation catalysed by PriA, in which an enzyme is shared by two amino acid biosynthetic pathways, several paralogous enzymes with the potential to account for the first step of tryptophan biosynthesis from chorismate were found on the genome of S. coelicolor. These chorismate-utilising enzymes are investigated in Chapter V. Mutational analysis of some of this paralogues is reported and it is anticipated that the analysis and results reported therein will serve to direct future experiments aimed at identifying the trpE paralogue encoding the enzyme anthranilate synthase. Chapter VI reports on the identification of the proC gene involved in the last step of proline biosynthesis in S. coelicolor. The pyrroline-5-carboxylate reductase activity of the enzyme encoded by the putative proC gene was extensively characterised, with particular emphasis on the interaction between primary and secondary metabolism. Furthermore, mutational analysis of proC suggested that paralogues of this gene are present on the genome of this organism, since its deletion did not lead to an auxotrophic phenotype. Investigation of this observation showed that two paralogous enzymes encoded by i1vC-like genes, involved in biosynthesis of the branched-chain amino acids, are capable of compensating for the lack of proC. This is the first example of a physiological link between the biosynthesis of proline and the branched-chain amino acids. To sum up, the results reported in this thesis represent an advancement towards understanding the physiology of S. coelicolor as a model actinomycete, within a functional and structural genomics framework. They also offer evidence on the evolutionary principles that lead to the appearance of novel proteins and metabolic pathways in bacteria.

No description available.

The Streptomyces avidinii protein streptavidin binds the small molecule biotin (vitamin H / B₇) with extraordinary stability, resulting in the streptavidin-biotin interaction being one of the strongest non-covalent interactions known in nature (K_d ~ 10^-14 M). The stable and rapid biotin-binding, together with high resistance to heat, pH and proteolysis, has given streptavidin huge utility, both in vivo and in vitro. Accordingly, streptavidin has become a widely used tool in many different biotechnological applications. Streptavidin has also been the subject of extensive research efforts to glean insights into this paradigm for a high-affinity interaction, with over 200 mutants of the protein reported to date. Despite the high stability of the streptavidin-biotin interaction, it can and does fail under certain experimental conditions. For example, streptavidin-biotin dissociation is accelerated by an increased temperature or lower pH (conditions often encountered in cellular imaging experiments), and by mechanical stress, such as the shear force arising from fluid flow (encountered when streptavidin is used as a molecular anchor in biosensor chips and arrays). This study details efforts made at increasing further the utility of streptavidin, by increasing the stability of biotin and biotin-conjugate binding. A rational site-directed mutagenesis approach was used to create 27 mutants, with eight of these mutants possessing higher-stability biotin-binding. The most stable biotin-binding mutant was named traptavidin and was extensively characterised. Kinetic characterisation revealed traptavidin had a decreased dissociation rate from biotin and biotin-conjugates when compared to wildtype streptavidin, at both neutral pH and pH 5. Atomic force microscopy and molecular motor displacement assays revealed the traptavidin-biotin interaction possessed higher mechanical stability than the streptavidin-biotin interaction. Cellular imaging experiments revealed the non-specific cell binding properties of streptavidin were unchanged in traptavidin. X-ray crystallography was also used to generate structures of both apo- and biotinbound traptavidin at 1.5 Å resolution. The structures were analysed in detail and compared to the published structures of streptavidin, revealing the characteristics of traptavidin arose from the mutations stabilising a flexible loop over the biotin-binding pocket, as well as reducing the conformational change on biotin-binding to traptavidin. Traptavidin has the potential to replace streptavidin in many of its diverse applications, as well as providing an insight into the nature of ultra-stable noncovalent interactions.