Prenylated Flavin-dependent decarboxylases: Structure-guided engineering and synthetic applicability

The recently discovered prenylated flavin (prFMN) cofactor is utilised by UbiD enzyme family to catalyse non-oxidative decarboxylation of precursors of respiratory quinones. Mechanistic aspect of prFMN-mediated decarboxylation has attracted interests and studies of fungal ferulic acid decarboxylases (FDCs), members of the UbiD enzyme family reveal a rare enzymatic 1,3-dipolar cycloaddition mechanism for the decarboxylation of cinnamic aid. Please click Additional Files below to see the full abstract

Structure and mechanism of a canonical poly(ADP-ribose) glycohydrolase

Poly(ADP-ribosyl)ation is a reversible post-translational protein modification involved in the regulation of a number of cellular processes including DNA repair, chromatin structure, mitosis, transcription, checkpoint activation, apoptosis and asexual development. The reversion of poly(ADP-ribosyl)ation is catalysed by poly(ADP-ribose) (PAR) glycohydrolase (PARG), which specifically targets the unique PAR (1''-2') ribose-ribose bonds. Here we report the structure and mechanism of the first canonical PARG from the protozoan Tetrahymena thermophila. In addition, we reveal the structure of T. thermophila PARG in a complex with a novel rhodanine-containing mammalian PARG inhibitor RBPI-3. Our data demonstrate that the protozoan PARG represents a good model for human PARG and is therefore likely to prove useful in guiding structure-based discovery of new classes of PARG inhibitors

Synthetic Enzyme-Catalyzed CO2 Fixation Reactions.

In recent years, (de)carboxylases that catalyze reversible (de)carboxylation have been targeted for application as carboxylation catalysts. This has led to the development of proof-of-concept (bio)synthetic CO2 fixation routes for chemical production. However, further progress towards industrial application has been hampered by the thermodynamic constraint that accompanies fixing CO2 to organic molecules. In this Review, biocatalytic carboxylation methods are discussed with emphases on the diverse strategies devised to alleviate the inherent thermodynamic constraints and their application in synthetic CO2 -fixation cascades

Visualization of poly(ADP-ribose) bound to PARG reveals inherent balance between exo- and endo-glycohydrolase activities

Poly-ADP-ribosylation is a post-translational modification that regulates processes involved in genome stability. Breakdown of the poly(ADP-ribose) (PAR) polymer is catalysed by poly(ADP-ribose) glycohydrolase (PARG), whose endo-glycohydrolase activity generates PAR fragments. Here we present the crystal structure of PARG incorporating the PAR substrate. The two terminal ADP-ribose units of the polymeric substrate are bound in exo-mode. Biochemical and modelling studies reveal that PARG acts predominantly as an exo-glycohydrolase. This preference is linked to Phe902 (human numbering), which is responsible for low-affinity binding of the substrate in endo-mode. Our data reveal the mechanism of poly-ADP-ribosylation reversal, with ADP-ribose as the dominant product, and suggest that the release of apoptotic PAR fragments occurs at unusual PAR/PARG ratios

'Paying for the Emergency by displacing the Settlers' : global coffee and rural restructuring in late colonial Kenya.

Global coffee markets entered into a deep cyclical downturn from the mid 1950s. As producers, notably Brazil and Colombia, continued to increase their output, intense struggles arose among global competitors for larger slices of a contracting market. The prospect of an economic catastrophe, following the release of Brazil's surplus stocks, preoccupied Kenya's colonial government, which was dependent on tax revenues derived from coffee sales, and was less able to support the settler-dominated industry in the face of the increased costs incurred by the Mau Mau Emergency after 1952. This left European settlers exposed, with many barely able to recover their costs of production. What began as a counter-insurgency strategy, by allowing an elite of African farmers to grow Arabica coffee (a privilege formerly reserved to settlers) was enlarged and accelerated in response to unrelenting global market pressures. These compelled the colonial government to beckon low-cost African farmers into coffee production, in a bid to save its tax base and ensure the survival of the coffee sector. Even though the Coffee Marketing Board confiscated much of their income, African farmers proved well able to rally family labour and achieve surpluses. Rationalization of production and the re-organization of the commodity chain to maintain high quality at lower cost were decisive in both reconfiguring the economic and social relationships that underpinned Kenya's independence in 1963 and securing the country's place on the world market. The aim here is to explain the crisis, and its grip on Kenya's economy during the transition to independence and beyond

The role of ADP-ribosylation in regulating DNA interstrand crosslink repair

ADP-ribosylation by ADP-ribosyltransferases (ARTs) has a well-established role in DNA strand break repair by promoting enrichment of repair factors at damage sites through ADP-ribose interaction domains. Here we exploit the simple eukaryote Dictyostelium to uncover a role for ADP-ribosylation in regulating DNA interstrand crosslink repair and redundancy of this pathway with non-homologous end-joining (NHEJ). In silico searches identify a protein that contains a permutated macrodomain (Aprataxin/APLF-and-PNKP-Like protein; APL). Structural analysis reveals permutated macrodomains retain features associated with ADP-ribose interactions and APL is capable of binding poly-ADP-ribose through its macrodomain. APL is enriched in chromatin in response to cisplatin, an agent that induces DNA interstrand crosslinks (ICLs). This is dependent on the macrodomain of APL, and the ART Adprt2, indicating a role for ADP-ribosylation in the cellular response to cisplatin. Although adprt2− cells are sensitive to cisplatin, ADP-ribosylation is evident in these cells due to redundant signalling by the DSB-responsive ART Adprt1a, promoting NHEJ-mediated repair. These data implicate ADP-ribosylation in DNA ICL repair and identify NHEJ can function to resolve this form of DNA damage in the absence of Adprt2