Oxidative C-H hydroxylation of methyl groups, followed by their removal from DNA, RNA or histones, is an epigenetic process critical to transcriptional reprogramming and cell fate determination. This reaction is catalyzed by Fe(II)-dependent dioxygenases using the essential metabolite 2-ketoglutarate (2KG) as a cofactor. Given that the human genome encodes for more than 60 2KG-dependent dioxygenases, assigning their individual functions remains a significant challenge. Here we describe a protein-ligand interface engineering approach to break the biochemical degeneracy of these enzymes. Using histone lysine demethylase 4 (KDM4) as a proof-of-concept, we show that the enzyme active site can be expanded to employ bulky 2KG analogues that do not sensitize wild type demethylases. We establish the orthogonality, substrate specificity and catalytic competency of the engineered demethylation apparatus in biochemical assays. We further demonstrate demethylation of cognate substrates in physiologically relevant settings. Our results provide a para-digm for rapid and conditional manipulation of histone deme-thylases to uncloak their isoform-specific functions.

The hydrophobic pocket of the epigenetic reader protein BRD4 has been engineered to carry a photosensitive amino acid to identify novel interacting partners, providing mechanistic insights into BRD4’s function in transcription and beyond.

Enzymatic methylation at carbon five on cytosine (5mC) in DNA is a hallmark of mammalian epigenetic programming and is critical to gene regulation during early embryonic development. It has recently been shown that dynamic erasure of 5mC by three members of the ten-eleven translocation (TET) family plays a key role in cellular differentiation. TET enzymes belong to Fe (II)- and 2-ketoglutarate (2KG) dependent dioxygenases that successively oxidize 5mC to 5-hydroxymethyl cytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxycytosine (5CaC), thus providing a chemical basis for the removal of 5mC which once was thought to be a permanent mark in mammalian genome. Since then a wide range of biochemical assays have been developed to characterize TET activity. Majority of these methods require multi-step processing to detect and quantify the TET-mediated oxidized products. In this study, we have developed a MALDI mass spectrometry based method that directly measures the TET activity with high sensitivity while eliminating the need for any intermediate processing steps. We applied this method to the measurement of enzymatic activity of TET1 and 3, Michaleis-Menten parameters (KM and kcat) of TET-2KG pairs and inhibitory concentration (IC50) of known small-molecule inhibitors of TETs. We further demonstrated the suitability of the assay to analyze chemoenzymatic labeling of 5hmC by β-glucosyltransferase, highlighting the potential for broad application of our method in deconvoluting the functions of novel DNA demethylases.

The potential for active pharmaceutical intermediates and active ingredients to contain low levels of N-nitrosamines is a topic of continued interest from industry and regulatory authorities, which has led us to generate experimental data demonstrating that the published kinetic model of dialkylamine nitrosation is conservative and may overpredict the level of N-nitrosamine formation that will actually occur. Additionally, studies comparing the nitrosation of simple trialkylamines to that of the relevant dialkylamines have demonstrated that trialkylamines do indeed undergo nitrosative dealkylation to form N-nitrosamines but at a rate that is at least 500 times lower than for the related dialkylamines.