Regulation of Glutamine and Glutamate Metabolism by GlnR and GlnA in Streptococcus pneumoniae

Abstract

Several genes involved in nitrogen metabolism are known to contribute to the virulence of pathogenic bacteria. Here, we studied the function of the nitrogen regulatory protein GlnR in the Gram-positive human pathogen Streptococcus pneumoniae. We demonstrate that GlnR mediates transcriptional repression of genes involved in glutamine synthesis and uptake (glnA and glnPQ), glutamate synthesis (gdhA), and the gene encoding the pentose phosphate pathway enzyme Zwf, which forms an operon with glnPQ. Moreover, the expression of gdhA is also repressed by the pleiotropic regulator CodY. The GlnR-dependent regulation occurs through a conserved operator sequence and is responsive to the concentration of glutamate, glutamine, and ammonium in the growth medium. By means of in vitro binding studies and transcriptional analyses, we show that the regulatory function of GlnR is dependent on GlnA. Mutants of glnA and glnP displayed significantly reduced adhesion to Detroit 562 human pharyngeal epithelial cells, suggesting a role for these genes in the colonization of the host by S. pneumoniae. Thus, our results provide a thorough insight into the regulation of glutamine and glutamate metabolism of S. pneumoniae mediated by both GlnR and GlnA.

Bacillus subtilis glutamine synthetase regulates its own synthesis by acting as a chaperone to stabilize GlnR–DNA complexes

“…These results indicate that FBI-GS stimulates the ability of GlnR to bind to DNA. In contrast to previous studies that reported that GS has a small stimulatory effect on the DNA-binding activity of GlnR (5,16,17), significant activation of GlnR DNA-binding activity was only observed in the presence of FBI-GS. In addition, this activation of GlnR DNA-binding activity was only observed with GlnR protein that had been purified to homogeneity (data not shown).…”

“…Although previous genetic evidence indicated that the GlnRdependent repression of gene expression requires GS (2,15,16), it was unclear whether GS played a direct role in this regulation or whether glnA mutants indirectly altered gene expression by changing the physiological state of the cell. The experiments presented here demonstrate that GS enhances the DNA-binding activity of GlnR through a direct interaction with FBI-GS that stabilizes GlnR-DNA complexes.…”

“…Previously published biochemical studies have demonstrated a small stimulation of GlnR DNA binding to glnRA promoter DNA in the presence of GS (5,16,17). The biological significance of these observations is unclear because the molecular mechanisms responsible for the GS-dependent enhancement of GlnR DNA-binding activity and the transduction of the nitrogen signal to GlnR were not identified.…”

“…This dicistronic operon is found within the genomes of many low-GC Gram-positive bacteria (14). Genetic studies indicate that both GlnR and GS are required for the repression of glnRA expression (2,9,15,16).…”

Influência do cobre no padrão de expressão de genes envolvidos na interação de Paracoccidioides brasiliensis com a matriz extracelular

“…É a proteína chave das vias oxidativa da pentose e da Entner-Doudoroff, presente em bactérias, Archaea e em todas as células eucarióticas (HANSEN et al, 2002). Trabalhos têm verificado que cepas mutantes para G6PD de E. coli, Salmonella typhimurium, e Pseudomonas aeruginosa são mais suscetíveis a espécies intermediárias de oxigênio e nitrogênio, sugerindo que esta enzima tem papel importante durante o estresse oxidativo (GREENBERG et al, 1990;LUNDBERG et al, 1999;MA et al, 1998 dentre os quais está a via metabólica da glutamina (HENDRIKSEN et al, 2008;KLOOSTERMAN et al, 2006;TAMURA et al, 2002;TULLIUS et al, 2003). Em estreptococos do grupo B, foi sugerido que o transportador de glutamato tinha papel importante para a aderência a fibronectina e para virulência em animais de experimentação (TAMURA et al, 2002).…”