Cloning, expression, purification, crystallization and preliminary X-ray crystallographic analysis of isocitrate dehydrogenase 2 (Rv0066c) from Mycobacterium tuberculosis

Metabolomics of Central Carbon Metabolism in Mycobacterium tuberculosis

Metabolism is a biochemical activity of all cells, thought to fuel the physiologic needs of a given cell in a quantitative, rather than qualitatively specific, manner. Mycobacterium tuberculosis is a chronic facultative intracellular pathogen that resides in humans as its only known host and reservoir. Within humans, M. tuberculosis resides chiefly in the macrophage phagosome, the cell type and compartment most committed to its eradication. M. tuberculosis thus occupies the majority of its decades-long life cycle in a state of slowed or arrested replication. At the same time, M. tuberculosis remains poised to reenter the cell cycle to ensure its propagation as a species. M. tuberculosis has thus evolved its metabolic network to both maintain and propagate its survival as a species within a single host. Knowledge of the specific ways in which its metabolic network serves these distinct though interdependent functions, however, remains highly incomplete. In this article we review existing knowledge of M. tuberculosis's central carbon metabolism as reported by studies of its basic genetic and biochemical composition, regulation, and organization, with the hope that such knowledge will inform our understanding of M. tuberculosis's ability to traverse the stringent and heterogeneous niches encountered in the host.

Control of carbon flux to glutamate excretion in Klebsiella pneumoniae: the role of the indigenous plasmid and its encoded isocitrate dehydrogenase

Klebsiella pneumoniae (NCTC, CL687/80) harbors a large indigenous plasmid (p(C3)), which in addition to encoding for citrate utilization, proline synthesis and glutamate excretion, it uniquely carries the structural gene (icd); encoding isocitrate dehydrogenase (ICDH). Flux analysis revealed that ICDH, despite its role in the generation of NADPH required for glutamate dehydrogenase, is not rate-limiting (controlling) in central metabolism as evidenced by a negative flux control coefficient and an adverse effect of overexpression (14-fold) on glutamate excretion. More significantly, however, this paper presents, for the first time, clear evidence that the accumulation of glutamate and its subsequent excretion is associated with the C3 plasmid-encoded regulatory elements, which trigger a shift-down in the activity of α-ketoglutarate dehydrogenase, both in the K. pneumoniae parental strain as well as in the E. coli exconjugants strains. This finding opens the door for the exploitation of regulatory elements as a tool for manipulating flux in microbial cell factories.