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Organohalide chemistry underpins many industrial and agricultural processes, and a large proportion of environmental pollutants are organohalides (1). Nevertheless, organohalide chemistry is not exclusively of anthropogenic origin, with natural abiotic and biological processes contributing to the global halide cycle (2, 3). Reductive dehalogenases are responsible for biological dehalogenation in organohalide respiring bacteria (4, 5), with substrates including polychlorinated biphenyls or dioxins (6, 7). Reductive dehalogenases form a distinct subfamily of cobalamin (B12)-dependent enzymes that are usually membrane associated and oxygen sensitive, hindering detailed studies (8, 12). Here we report the characterization of a soluble, oxygen-tolerant reductive dehalogenase and, by combining structure determination with EPR (electron paramagnetic resonance) spectroscopy and simulation, show that a direct interaction between the cobalamin cobalt and the substrate halogen underpins catalysis. In contrast to the carbon-cobalt bond chemistry catalysed by the other cobalamin-dependent subfamilies (13), we propose that reductive dehalogenases achieve reduction of the organohalide substrate via halogen-cobalt bond formation. This presents a new model in both organohalide and cobalamin (bio)chemistry that will guide future exploitation of these enzymes in bioremediation or biocatalysis., Cobalamin consists of a cobalt ion coordinated by a tetrapyrrole-derived macrocycle and readily forms a weak organometallic C-Co(III) bond (14). This bond can be homolytically or heterolytically cleaved and the [...]

Inhibition of kynurenine 3-monooxygenase (KMO), an enzyme in the eukaryotic tryptophan catabolic pathway (that is, kynurenine pathway), leads to amelioration of Huntington's-disease-relevant phenotypes in yeast, fruitfly and mouse models (1-5), [...]

Post-translational modification of proteins by poly(ADP-ribosyl) ation regulates many cellular pathways that are critical for genome stability, including DNA repair, chromatin structure, mitosis and apoptosis (1). Poly(ADP-ribose) (PAR) is composed of repeating ADP-ribose units linked via a unique glycosidic ribose-ribose bond, and is synthesized from NAD by PAR polymerases (1,2). PAR glycohydrolase (PARG) is the only protein capable of specific hydrolysis of the ribose-ribose bonds present in PAR chains; its deficiency leads to cell death (3,4). Here we show that filamentous fungi and a number of bacteria possess a divergent form of PARG that has all the main characteristics of the human PARG enzyme. We present the first PARG crystal structure (derived from the bacterium Thermomonospora curvata), which reveals that the PARG catalytic domain is a distant member of the ubiquitous ADP-ribose-binding macrodomain family (5,6). High-resolution structures of T. curvata PARG in complexes with ADP-ribose and the PARG inhibitor ADP-HPD, complemented by biochemical studies, allow us to propose a model for PAR binding and catalysis by PARG. The insights into the PARG structure and catalytic mechanism should greatly improve our understanding of how PARG activity controls reversible protein poly(ADP-ribosyl) ation and potentially of how the defects in this regulation are linked to human disease., Whereas the mechanism and functional aspects of PAR synthesis have been extensively characterized, the present understanding of the PAR-degradation pathways catalysed by PARG is comparatively poor. Until now, the catalytic [...]

Author(s): Mary Ortmayer [1]; Pierre Lafite [1]; Binuraj R. K. Menon [1]; Tewes Tralau [1]; Karl Fisher [1]; Lukas Denkhaus [1]; Nigel S. Scrutton [1]; Stephen E. J. Rigby [1]; [...]

Author(s): Karl A. P. Payne [1]; Mark D. White [1]; Karl Fisher [1]; Basile Khara [1]; Samuel S. Bailey [1]; David Parker [2]; Nicholas J. W. Rattray [1]; Drupad K. [...]