A proof of concept study to assess the potential of PCR testing to detect natural Mycobacterium bovis infection in South American camelids.

BACKGROUND: Cases of Mycobacterium bovis infection South American camelids have been increasing in Great Britain. Current antemortem immunological tests have some limitations. Cases at post mortem examination frequently show extensive pathology. The feasibility of detecting Mycobacterium bovis DNA in clinical samples was investigated. FINDINGS: A sensitive extraction methodology was developed and used on nasal swabs and faeces taken post-mortem to assess the potential for a PCR test to detect Mycobacterium bovis in clinical samples. The gross pathology of the studied South American camelids was scored and a significantly greater proportion of South American camelids with more severe pathology were positive in both the nasal swab and faecal PCR tests. A combination of the nasal swab and faecal PCR tests detected 63.9% of all the South American camelids with pathology that were tested. CONCLUSIONS: The results suggest that antemortem diagnosis of Mycobacterium bovis in South American camelids may be possible using a PCR test on clinical samples, however more work is required to determine sensitivity and specificity, and the practicalities of applying the test in the field.

X-ray structure of Fasciola hepatica Sigma class glutathione transferase 1 reveals a disulfide bond to support stability in gastro-intestinal environment.

Sigma class GST (Prostaglandin D synthase), FhGST-S1, is present in the excretory-secretory products (ES) of the liver fluke parasite Fasciola hepatica as cargo of extracellular vesicles (EVs) released by the parasite. FhGST-S1 has a well characterised role in the modulation of the immune response; a key fluke intercession that allows for establishment and development within their hosts. We have resolved the three-dimensional structure of FhGST-S1 in complex with its co-factor glutathione, in complex with a glutathione-cysteine adduct, and in a glutathione disulfide complex in order to initiate a research pipeline to mechanistically understand how FhGST-S1 functions within the host environment and to rationally design selective inhibitors. The overall fold of FhGST-S1 shows high structural similarity to other Sigma class GSTs. However, a unique interdomain disulfide bond was found in the FhGST-S1 which could stabilise the structure within the host gastro-intestinal environment. The position of the two domains of the protein with respect to each other is seen to be crucial in the formation of the active site cleft of the enzyme. The interdomain disulfide bond raises the possibility of oxidative regulation of the active site of this GST protein.

The Fasciola hepatica thioredoxin: High resolution structure reveals two oxidation states.

The Fasciola hepatica thioredoxin protein structure has been determined to 1.45A resolution. This is the first example of a single crystal structure to show the active site cysteine residues in both the reduced and disulfide oxidised form. Consistent with this observation the process of oxidation appears to require very little rearrangement of the surrounding protein structure. The F. hepatica thioredoxin structure has been compared to other thioredoxin protein structures already known and is found to be highly conserved. The F. hepatica protein is most similar to that of the thioredoxin from its human and animal hosts but it resembles other parasitic thioredoxins with regard to having no additional cysteine residues and is therefore not regulated by transient disulfide bond formation as proposed for thioredoxins from higher eukaryotic species.

Investigation of the redox centres of periplasmic selenate reductase from Thauera selenatis by EPR spectroscopy.

Periplasmic SER (selenate reductase) from Thauera selenatis is classified as a member of the Tat (twin-arginine translocase)-translocated (Type II) molybdoenzymes and comprises three subunits each containing redox cofactors. Variable-temperature X-band EPR spectra of the purified SER complex showed features attributable to centres [3Fe-4S]1+, [4Fe-4S]1+, Mo(V) and haem-b. EPR-monitored redox-potentiometric titration of the SerABC complex (SerA-SerB-SerC, a hetero-trimetric complex of alphabetagamma subunits) revealed that the [3Fe-4S] cluster (FS4, iron-sulfur cluster 4) titrated as n=1 Nernstian component with a midpoint redox potential (E(m)) of +118+/-10 mV for the [3Fe-4S]1+/0 couple. A [4Fe-4S]1+ cluster EPR signal developed over a range of potentials between 300 and -200 mV and was best fitted to two sequential Nernstian n=1 curves with midpoint redox potentials of +183+/-10 mV (FS1) and -51+/-10 mV (FS3) for the two [4Fe-4S]1+/2+ cluster couples. Upon further reduction, the observed signal intensity of the [4Fe-4S]1+ cluster decreases. This change in intensity can again be fitted to an n=1 Nernstian component with a midpoint potential (E(m)) of about -356 mV (FS2). It is considered likely that, at low redox potential (E(m) less than -300 mV), the remaining oxidized cluster is reduced (spin S=1/2) and strongly spin-couples to a neighbouring [4Fe-4S]1+ cluster rendering both centres EPR-silent. The involvement of both [3Fe-4S] and [4Fe-4S] clusters in electron transfer to the active site of the periplasmic SER was demonstrated by the re-oxidation of the clusters under anaerobic selenate turnover conditions. Attempts to detect a high-spin [4Fe-4S] cluster (FS0) in SerA at low temperature (5 K) and high power (100 mW) were unsuccessful. The Mo(V) EPR recorded at 60 K, in samples poised at pH 6.0, displays principal g values of g3 approximately 1.999, g2 approximately 1.996 and g1 approximately 1.965 (g(av) 1.9867). The dominant features at g2 and g3 are not split, but hyperfine splitting is observed in the g1 region of the spectrum and can be best simulated as arising from a single proton with a coupling constant of A1 (1H)=1.014 mT. The presence of the haem-b moiety in SerC was demonstrated by the detection of a signal at g approximately 3.33 and is consistent with haem co-ordinated by methionine and lysine axial ligands. The combined evidence from EPR analysis and sequence alignments supports the assignment of the periplasmic SER as a member of the Type II molybdoenzymes and provides the first spectro-potentiometric insight into an enzyme that catalyses a key reductive reaction in the biogeochemical selenium cycle.

The crystal structure of a (-) gamma-lactamase from an Aureobacterium species reveals a tetrahedral intermediate in the active site.

The structure of the recombinant (-) gamma-lactamase from an Aureobacterium species has been solved at 1.73A resolution in the cubic space group F23 with unit cell parameters a=b=c=240.6A. The trimeric enzyme has an alpha/beta hydrolase fold and closely resembles the cofactor free haloperoxidases. The structure has been solved in complex with a covalently bound ligand originating from the host cell and also in the unligated form. The associated density in the former structure has been interpreted as the two-ring ligand (3aR,7aS)-3a,4,7,7a-tetrahydro-benzo [1,3] dioxol-2-one which forms a tetrahedral complex with OG of the catalytic Ser98. Soaks of these crystals with the industrial substrate gamma-lactam or its structural analogue, norcamphor, result in the displacement of the ligand from the enzyme active site, thereby allowing determination of the unligated structure. The presence of the ligand in the active site protects the enzyme from serine hydrolase inhibitors. Cyclic ethylene carbonate, the first ring of the ligand, was shown to be a substrate of the enzyme.

Evaluation of MALDI-ToF as a method for the identification of bacteria in the veterinary diagnostic laboratory.

Matrix-Assisted Laser Desorption Ionisation-Time of Flight (MALDI-ToF) Mass Spectrometry with Bruker MALDI Biotyper software was evaluated as a method for identifying veterinary bacteria. For 620 isolates (~100 bacterial species), identification by MALDI-ToF and non-16S rDNA methods (mainly phenotypic/biochemical) agreed to species-level (95.3%) and to species/genus-level (100%), but in the absence of 16S rDNA as a gold standard. For a further panel of 107 anaerobes and 234 aerobes (~100 bacteria species) using 16S rDNA results as the gold standard, MALDI-ToF/biochemical tests showed 97.8/96.6% species-level and 99.6/93.5% genus-level agreement for aerobes and 95.3/93.6% species-level and 100/95.3% genus-level agreement for anaerobes compared to the gold standard. Where results were obtained from direct spots, direct spots overlaid with formic acid and extracts, 89.4% of 180 aerobes and 90.1% of 152 anaerobes were identified by MALDI-ToF. MALDI-ToF was shown to be a rapid and reliable method to identify veterinary bacteria.

Synthesis and characterisation of a ligand that forms a stable tetrahedral intermediate in the active site of the Aureobacterium species (-) gamma-lactamase.

The crystal structure of a (-) gamma-lactamase from an Aureobacterium species showed a molecule bound covalently to the active site serine residue. This enzyme complex represented the first structure of a stably bound tetrahedral intermediate for an alpha/beta hydrolase fold enzyme. The structural elucidation of tetrahedral intermediates is important for the understanding of enzymatic mechanism, substrate recognition and enzyme inhibition. In this paper, we report the synthesis and subsequent characterisation of (3aR,7aS)-3a,4,7,7a-tetrahydrobenzo-[1,3]-dioxol-2-one (BD1), the molecule modelled into the Aureobacterium (-) gamma-lactamase active site. This molecule has been confirmed to be an inhibitor and to be displaced from the enzyme by the racemic gamma-lactam substrate.