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David G Russell

Publications and source records attributed to David G Russell.

23 records · Page 2Linked to original sources
PubMed2003

pckA-deficient Mycobacterium bovis BCG shows attenuated virulence in mice and in macrophages.

Phosphoenolpyruvate carboxykinase (PEPCK) catalyses the reversible decarboxylation and phosphorylation of oxaloacetate (OAA) to form phosphoenolpyruvate (PEP). In this study, the regulation of the PEPCK-encoding gene pckA was examined through the evaluation of green fluorescent protein expression driven by the pckA promoter. The results showed that pckA was upregulated by acetate or palmitate but downregulated by glucose. Deletion of the pckA gene of Mycobacterium bovis BCG led to a reduction in the capacity of the bacteria to infect and survive in macrophages. Moreover, mice infected with DeltapckA BCG were able to reduce the bacterial load much more effectively than mice infected with the parental wild-type bacteria. This attenuated virulence was reflected in the degree of pathology, where granuloma formation was diminished both in numbers and degree. The data indicate that PEPCK activity is important during establishment of infection. Whether its role is in the gluconeogenic pathway for carbohydrate formation or in the conversion of PEP to OAA to maintain the TCA cycle remains to be determined.

Acetic Acid↗
PubMed2002

Biochemical and structural studies of malate synthase from Mycobacterium tuberculosis.

Establishment or maintenance of a persistent infection by Mycobacterium tuberculosis requires the glyoxylate pathway. This is a bypass of the tricarboxylic acid cycle in which isocitrate lyase and malate synthase (GlcB) catalyze the net incorporation of carbon during growth of microorganisms on acetate or fatty acids as the primary carbon source. The glcB gene from M. tuberculosis, which encodes malate synthase, was cloned, and GlcB was expressed in Escherichia coli. The influence of media conditions on expression in M. tuberculosis indicated that this enzyme is regulated differentially to isocitrate lyase. Purified GlcB had K(m) values of 57 and 30 microm for its substrates glyoxylate and acetyl coenzyme A, respectively, and was inhibited by bromopyruvate, oxalate, and phosphoenolpyruvate. The GlcB structure was solved to 2.1-A resolution in the presence of glyoxylate and magnesium. We also report the structure of GlcB in complex with the products of the reaction, coenzyme A and malate, solved to 2.7-A resolution. Coenzyme A binds in a bent conformation, and the details of its interactions are described, together with implications on the enzyme mechanism.

Amino Acid Sequence↗
PubMed2002

Mycobacterium and the coat of many lipids.

Pathogenic Mycobacterium reside inside vacuoles in their host macrophages. These vacuoles fail to fuse with lysosomes yet interact with early endosomes. Glycoconjugates released by the intracellular bacilli traffic through the host cell and are released through exocytosis. These molecules represent both antigens for immune recognition and modulators of immune function. The molecules play key roles in the induction and maintenance of the granuloma, a tissue response that limits bacterial spread yet ensures persistence of the infection.

Animals↗
PubMed2002

Association of a macrophage galactoside-binding protein with Mycobacterium-containing phagosomes.

Mycobacteria reside intracellularly in a vacuole that allows it to circumvent the antimicrobial environment of the host macrophage. Although the mycobacterial phagosome exhibits selective fusion with vesicles of the endosomal system, identification of host and bacterial factors associated with phagosome bio-genesis is limited. To identify these potential factors, mAbs were generated to a membrane preparation of mycobacterial phagosomes isolated from M. tuberculosis-infected macrophages. A mAb recognizing a 32-35 kDa macrophage protein associated with the phagosomal membrane of Mycobacterium was identified. N-terminal sequence analysis identified this protein as Mac-2 or galectin-3, a galactoside-binding protein of macrophages. Galectin-3 (gal-3) was shown to accumulate in Mycobacterium-containing phagosomes during the course of infection. This accumulation was specific for phagosomes containing live mycobacteria and occurred primarily at the cytosolic face of the phagosome membrane. In addition, bind-ing of gal-3 to mycobacterial phosphatidylinositol mannosides (PIMs) demonstrated a novel interaction between host carbohydrate-binding proteins and released mycobacterial glycolipids. Infection of macrophages from gal-3-deficient mice indicated that the protein did not play a role in infection in vitro. In contrast, infection of gal-3-deficient mice revealed a reduced capacity to clear late but not early infection.

Animals↗