All four Mycobacterium tuberculosis glnA genes encode glutamine synthetase activities but only GlnA1 is abundantly expressed and essential for bacterial homeostasis

Abstract

SummaryGlutamine synthetases (GS) are ubiquitous enzymes that play a central role in every cell's nitrogen metabolism. We have investigated the expression and activity of all four genomic Mycobacterium tuberculosis GS -GlnA1, GlnA2, GlnA3 and GlnA4 -and four enzymes regulating GS activity and/or nitrogen and glutamate metabolism -adenylyl transferase (GlnE), γ γ γ γ -glutamylcysteine synthase (GshA), UDP-N -acetylmuramoylalanine-D -glutamate ligase (MurD) and glutamate racemase (MurI). All eight genes are located in multigene operons except for gln A1, and all are transcribed in M. tuberculosis ; however, some are not translated or translated at such low levels that the enzymes escape detection. Of the four GS, only GlnA1 can be detected. Each of the eight genes, as well as the gln A1-gln E-gln A2 cluster, was expressed separately in Mycobacterium smegmatis , and its gene product was characterized and assayed for enzymatic activity by analysing the reaction products. In

Regulation of nitrogen metabolism in Mycobacterium tuberculosis: A comparison with mechanisms in Corynebacterium glutamicum and Streptomyces coelicolor

“…Harth et al (22) have investigated the use of methionine-S,R-sulphoximine (MSO) as a novel antibiotic strategy since MSO strongly inhibits all four glutamine synthetases found in M. tuberculosis. MSO binds irreversibly to, and inhibits, the extracellular mycobacterial glutamine synthetase while not significantly affecting intracellular glutamine synthetase activity (45).…”

“…Only GlnA1, however appears to be the functional enzyme involved in nitrogen metabolism in vivo in these organisms (22,23). Construction of an M. tuberculosis glnA1 mutant resulted in a bacterium auxotrophic for glutamine (10) thereby demonstrating its central role in nitrogen assimilation.…”

Glutamine synthetase encoded by glnA-1 is necessary for cell wall resistance and pathogenicity of Mycobacterium bovis

“…All GSs are multimeric enzymes and catalyse synthesis of L-glutamine, while GlnA2 catalyses the synthesis of D-glutamine and isoglutamine. Only glnA-1 has been shown to be essential for M. tuberculosis growth (Harth et al, 2005). Disruption of glnA-1 in M. tuberculosis results in glutamine auxotrophy, indicating its role in the synthesis of glutamine for the bacillus (Tullius et al, 2003).…”

Sirtuin-dependent reversible lysine acetylation of glutamine synthetases reveals an autofeedback loop in nitrogen metabolism

“…Actinomycetes generally contain one GSI-β enzyme (GlnA1) and two or three GSII enzymes. In many species of actinomycetes, such as M. tuberculosis, only the glnA1 gene (encoding a GSI-β) has been shown to be essential for growth, whereas the genes encoding GSII enzymes are not (29). GSI-β plays a central and essential role in nitrogen metabolism in actinomycetes because it not only controls glutamine synthesis, but also serves as the nitrogen signal for GlnR activation.…”