Barrier-to-Autointegration Factor Proteome Reveals Chromatin-Regulatory Partners

Nuclear lamin filaments and associated proteins form a nucleoskeletal (“lamina”) network required for transcription, replication, chromatin organization and epigenetic regulation in metazoans. Lamina defects cause human disease (“laminopathies”) and are linked to aging. Barrier-to-autointegration factor (BAF) is a mobile and essential component of the nuclear lamina that binds directly to histones, lamins and LEM-domain proteins, including the inner nuclear membrane protein emerin, and has roles in chromatin structure, mitosis and gene regulation. To understand BAF's mechanisms of action, BAF associated proteins were affinity-purified from HeLa cell nuclear lysates using BAF-conjugated beads, and identified by tandem mass spectrometry or independently identified and quantified using the iTRAQ method. We recovered A- and B-type lamins and core histones, all known to bind BAF directly, plus four human transcription factors (Requiem, NonO, p15, LEDGF), disease-linked proteins (e.g., Huntingtin, Treacle) and several proteins and enzymes that regulate chromatin. Association with endogenous BAF was independently validated by co-immunoprecipitation from HeLa cells for seven candidates including Requiem, poly(ADP-ribose) polymerase 1 (PARP1), retinoblastoma binding protein 4 (RBBP4), damage-specific DNA binding protein 1 (DDB1) and DDB2. Interestingly, endogenous BAF and emerin each associated with DDB2 and CUL4A in a UV- and time-dependent manner, suggesting BAF and emerin have dynamic roles in genome integrity and might help couple DNA damage responses to the nuclear lamina network. We conclude this proteome is a rich source of candidate partners for BAF and potentially also A- and B-type lamins, which may reveal how chromatin regulation and genome integrity are linked to nuclear structure

Bringing biocatalytic deuteration into the toolbox of asymmetric isotopic labelling techniques

Enzymes dependent on nicotinamide cofactors are important components of the expanding range of asymmetric synthetic techniques. New challenges in asymmetric catalysis are arising in the field of deuterium labelling, where compounds bearing deuterium (2H) atoms at chiral centres are becoming increasingly desirable targets for pharmaceutical and analytical chemists. However, utilisation of NADH-dependent enzymes for 2H-labelling is not straightforward, owing to difficulties in supplying a suitably isotopically-labelled cofactor ([4-2H]-NADH). Here we report on a strategy that combines a clean reductant (H2) with a cheap source of 2H-atoms (2H2O) to generate and recycle [4-2H]-NADH. By coupling [4-2H]-NADH-recycling to an array of C=O, C=N, and C=C bond reductases, we demonstrate asymmetric deuteration across a range of organic molecules under ambient conditions with near-perfect chemo-, stereo- and isotopic selectivity. We demonstrate the synthetic utility of the system by applying it in the isolation of the heavy drug (1S,3'R)-[2',2',3'-2H3]-solifenacin fumarate on a preparative scale