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Abstract: Diamond Light Source is a 3 GeV electron storage ring, which has been successfully operating in top-up mode since October 2008, having previously operated in decay mode only. Although in the UK there is no legal requirement to submit a safety case to the relevant authority (the Health and Safety Executive) when implementing top-up operation for the first time, it is required to keep doses ALARP and within the 1 mSv annual dose limit which Diamond has set for all staff, users and visitors. Prior to operating Diamond in top- up mode, a study of the radiological safety implications was carried out to ensure that these requirements could be met. The study involved calculation using FLUKA of dose rates arising from accidental beam losses. These losses took the form of either continuous losses in a front end arising from poor injection, or loss of a single injected electron pulse into a beamline optics hutch. In addition to the calculations, dose rate measurements were made outside beamline hutches under conditions of deliberately engineered beam losses in front ends, intended to compare as closely as possible with those modelled. As a result of this study, a number of changes to Diamond’s radiation monitoring regime were proposed and implemented before top-up operation was permitted. The study also helped to define the limits within which top-up would be permitted to operate.

Open Access

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Abstract: Klebsiella pneumoniae is a Gram-negative bacterium that is responsible for a range of common infections, including pulmonary pneumonia, bloodstream infections and meningitis. Certain strains of Klebsiella have become highly resistant to antibiotics. Despite the vast amount of research carried out on this class of bacteria, the molecular structure of its topoisomerase IV, a type II topoisomerase essential for catalysing chromosomal segregation, had remained unknown. In this paper, the structure of its DNA-cleavage complex is reported at 3.35 angstrom resolution. The complex is comprised of ParC breakage-reunion and ParE TOPRIM domains of K. pneumoniae topoisomerase IV with DNA stabilized by levofloxacin, a broad-spectrum fluoroquinolone antimicrobial agent. This complex is compared with a similar complex from Streptococcus pneumoniae, which has recently been solved.

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Abstract: Transaldolase B (TalB) and D-fructose-6-phosphate aldolase A (FSAA) from Escherichia coli are C-C bond-forming enzymes. Using kinetic inhibition studies and mass spectrometry, it is shown that enzyme variants of FSAA and TalB that exhibit D-fructose-6-phosphate aldolase activity are inhibited covalently and irreversibly by D-tagatose 6-phosphate (D-T6P), whereas no inhibition was observed for wild-type transaldolase B from E. coli. The crystal structure of the variant TalBF178Y with bound sugar phosphate was solved to a resolution of 1.46 Å and revealed a novel mode of covalent inhibition. The sugar is bound covalently via its C2 atom to the [epsilon]-NH2 group of the active-site residue Lys132. It is neither bound in the open-chain form nor as the closed-ring form of D-T6P, but has been converted to [beta]-D-galactofuranose 6-phosphate (D-G6P), a five-membered ring structure. The furanose ring of the covalent adduct is formed via a Heyns rearrangement and subsequent hemiacetal formation. This reaction is facilitated by Tyr178, which is proposed to act as acid-base catalyst. The crystal structure of the inhibitor complex is compared with the structure of the Schiff-base intermediate of TalBE96Q formed with the substrate D-fructose 6-phosphate determined to a resolution of 2.20 Å. This comparison highlights the differences in stereochemistry at the C4 atom of the ligand as an essential determinant for the formation of the inhibitor adduct in the active site of the enzyme.

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Abstract: Purpose: We aimed to characterize alterations in the posterior scleral collagen microstructure before detectable disease onset in a canine model of open-angle glaucoma caused by an ADAMTS10 mutation. Methods: Collagen orientation, anisotropy degree (proportion of preferentially aligned collagen), and relative density were measured at 0.4 mm spatial resolution using synchrotron wide-angle X-ray scattering. For statistical evaluation of structure parameters, regional averages of the peripapillary and mid-posterior sclera were compared between ADAMTS10 mutant (affected) dogs (n = 3) and age-matched (carrier) controls (n = 3). Results: No marked differences in the general pattern of preferential collagen fibril orientation were noted between the control and affected dogs. The peripapillary sclera of all specimens featured strongly aligned circumferential collagen ringing the optic nerve head. Collagen anisotropy was significantly reduced in the mid-posterior sclera of the affected dogs (carrier: 0.27 +/- 0.11; affected: 0.24 +/- 0.10; p = 0.032) but was not statistically significantly different in the peripapillary sclera (carrier: 0.46 +/- 0.15; affected: 0.45 +/- 0.17; p = 0.68). Collagen density was statistically significantly reduced in the affected dogs for the mid-posterior sclera (carrier: 28.1 +/- 9.14; affected: 18.3 +/- 5.12; p< 0.0001) and the peripapillary sclera (carrier: 34.6 +/- 9.34; affected: 21.1 +/- 6.97; p = 0.0002). Conclusions: Significant alterations in the posterior scleral collagen microstructure are present before the onset of clinical glaucoma in ADAMTS10 mutant dogs. A reduction in fibrous collagen density is likely an important contributory factor in the previously reported mechanical weakening of the sclera in this model. Baseline scleral abnormalities have the potential to interact with intraocular pressure (IOP) elevations in determining the course of glaucoma progression in animal models of the disease, and potentially in human glaucoma.