Structure of the C-terminal domain of the arginine repressor protein from Mycobacterium tuberculosis

The structure of the core domain of the arginine repressor protein from M. tuberculosis has been determined with (1.85 Å resolution) and without (2.15 Å resolution) the arginine corepressor bound. Three additional arginine molecules have been found to bind to the core domain hexamer at high (0.2 M) arginine concentration

Expression, purification and preliminary crystallographic analysis of N-acetylglucosamine-1-phosphate uridylyltransferase from Mycobacterium tuberculosis

N-Acetylglucosamine 1-phosphate uridyltransferase (GlmU) from M. tuberculosis H37Rv has been crystallized and preliminary X-ray crystallographic analysis has been performed. GlmU is a bi-domained bifunctional enzyme that is involved in the biosynthesis of UDP-N-acetylglucosamine, a precursor in peptidoglycan biosynthesis in M. tuberculosis

The crystal structures of ornithine carbamoyltransferase from Mycobacterium tuberculosis and its ternary complex with carbamoyl phosphate and L-norvaline reveal the enzyme's catalytic mechanism

Mycobacterium tuberculosis ornithine carbamoyltransferase (Mtb OTC) catalyzes the sixth step in arginine biosynthesis; it produces citrulline from carbamoyl phosphate (CP) and ornithine (ORN). Here, we report the crystal structures of Mtb OTC in orthorhombic (form I) and hexagonal (form II) space groups. The molecules in form II are complexed with CP and L-norvaline (NVA); the latter is a competitive inhibitor of OTC. The asymmetric unit in form I contains a pseudo hexamer with 32 point group symmetry. The CP and NVA in form II induce a remarkable conformational change in the 80s and the 240s loops with the displacement of these loops towards the active site. The displacement of these loops is strikingly different from that seen in other OTC structures. In addition, the ligands induce a domain closure of 4.4° in form II. Sequence comparison of active-site residues of Mtb OTC with several other OTCs of known structure reveals that they are virtually identical. The interactions involving the active-site residues of Mtb OTC with CP and NVA and a modeling study of ORN in the form II structure strongly rule out an earlier proposed mechanistic role of Cys264 in catalysis and suggest a possible mechanism for OTC. Our results strongly support the view that ORN with an already deprotonated Nε atom is the species that binds to the enzyme and that one of the phosphate oxygen atoms of CP is likely to be involved in accepting a proton from the doubly protonated Nε atom of ORN. We have interpreted this deprotonation as part of the collapse of the transition state of the reaction

Structure of Shiga Toxin Type 2 (Stx2) from \u3ci\u3eEscherichia coli\u3c/i\u3e O157:H7

Several serotypes of Escherichia coli produce protein toxins closely related to Shiga toxin (Stx) from Shigella dysenteriae serotype 1. These Stx-producing E. coli cause outbreaks of hemorrhagic colitis and hemolytic uremic syndrome in humans, with the latter being more likely if the E. coli produce Stx2 than if they only produce Stx1. To investigate the differences among the Stxs, which are all AB5 toxins, the crystal structure of Stx2 from E. coli O157:H7 was determined at 1.8-Å resolution and compared with the known structure of Stx. Our major finding was that, in contrast to Stx, the active site of the A-subunit of Stx2 is accessible in the holotoxin, and a molecule of formic acid and a water molecule mimic the binding of the adenine base of the substrate. Further, the A-subunit adopts a different orientation with respect to the B-subunits in Stx2 than in Stx, due to interactions between the carboxyl termini of the B-subunits and neighboring regions of the A-subunit. Of the three types of receptor-binding sites in the B-pentamer, one has a different conformation in Stx2 than in Stx, and the carboxyl terminus of the A-subunit binds at another. Any of these structural differences might result in different mechanisms of action of the two toxins and the development of hemolytic uremic syndrome upon exposure to Stx2

The molecular structure of Rv1873, a conserved hypothetical protein from Mycobacterium tuberculosis, at 1.38 Å resolution

SIRAS phasing techniques have been employed to determine the structure Mycobacterium tuberculosis Rv1873 at a resolution of 1.38 Å. We show that this conserved hypothetical protein of unknown function shows limited structural similarity to other molecules

The molecular structure of Rv2074, a probable pyridoxine 5′-phosphate oxidase from Mycobacterium tuberculosis, at 1.6 Å resolution

The crystal structure of a probable pyridoxine 5′-phosphate oxidase, Rv2074 from M. tuberculosis, has been solved by the two-wavelength anomalous dispersion method and has been refined at 1.6 Å resolution. Two citric acid molecules are bound fortuitously to the possible active site of Rv2074