Structural characterization of the Xi class glutathione transferase from the haloalkaliphilic archaeon Natrialba magadii

Xi class glutathione transferases (GSTs) are a recently identified group, within this large superfamily of enzymes, specifically endowed with glutathione-dependent reductase activity on glutathionyl-hydroquinone. Enzymes belonging to this group are widely distributed in bacteria, fungi, and plants but not in higher eukaryotes. Xi class GSTs are also frequently found in archaea and here we focus on the enzyme produced by the extreme haloalkaliphilic archaeon Natrialba magadii (NmGHR). We investigated its function and stability and determined its 3D structure in the apo form by X-ray crystallography. NmGHR displays the same fold of its mesophilic counterparts, is enriched in negatively charged residues, which are evenly distributed along the surface of the protein, and is characterized by a peculiar distribution of hydrophobic residues. A distinctive feature of haloalkaliphilic archaea is their preference for γ-glutamyl-cysteine over glutathione as a reducing thiol. Indeed we found that the N. magadii genome lacks a gene coding for glutathione synthase. Analysis of NmGHR structure suggests that the thiol binding site (G-site) of the enzyme is well suited for hosting γ-glutamyl-cysteine

New plate medium for growth and detection of urease activity of Helicobacter pylori.

A new medium for detection of urease activity and isolation of Helicobacter pylori is proposed. This medium, containing Columbia Agar Base, was supplemented with IsoVitaleX, hemin, urea, and phenol red (nonselective medium [NSM]). Both bacterial growth and color change were evaluated and compared with growth in the same medium supplemented with cefsulodin, vancomycin, polymyxin B sulfate, and amphotericin B (selective medium [SM]). Twenty-five recent clinical isolates and antral biopsy specimens from 33 patients who underwent endoscopy were examined. The isolates showed a rapid color change and good growth at 5 days of incubation with NSM and SM. H. pylori-positive biopsies revealed a color change within 36 h, and bacterial growth was better appreciated in NSM, but with more contaminating flora than in SM