5-Formylcytosine (f5C) modification is present in human mitochondrial methionine tRNA (mt-tRNAMet) and cytosolic leucine tRNA (ct-tRNALeu), with their formation mediated by NSUN3 and ALKBH1. f5C has also been detected in yeast mRNA and human tRNA, but its transcriptome-wide distribution in mammals has not been studied. Here we report f5C-seq, a quantitative sequencing method to map f5C transcriptome-wide in HeLa and mouse embryonic stem cells (mESCs). We show that f5C in RNA can be reduced to dihydrouracil (DHU) by pic-borane, and DHU can be exclusively read as T during reverse transcription (RT) reaction, allowing the detection and quantification of f5C sites by a unique C-to-T mutation signature. We validated f5C-seq by identifying and quantifying the two known f5C sites in tRNA, in which the f5C modification fractions dropped significantly in ALKBH1-depleted cells. By applying f5C-seq to chromatin-associated RNA (caRNA), we identified several highly modified f5C sites in HeLa and mouse embryonic stem cells (mESC).
Recent years have witnessed a renaissance of organic electrochemistry since the cheap, safe, sustainable electron could be employed as a traceless redox agent to facilitate redox conversions. Additionally, divergent selectivity could be achieved by tuning the potential or current of the electrochemical reaction. Compared to electrooxidation or electroreduction reactions, paired electrolysis represents a more practical and energy-efficient strategy that delivers the products by making use of both anodic and cathodic reactions simultaneously. This mini-review summarized the breakthroughs and recent advances in this fascinating field and mainly is divided into three parts: parallel, sequential, and convergent paired electrolysis.
The cover picture illustrates symbolically the critical step in π-acid catalysis as a bullfighting scene: a metal catalyst (the toreador) binds an alkyne and activates it for an attack by a nucleophile (the bull). Cover image by Dr. Igor Armiach.
Indole derivatives are fundamental structural units in many bioactive compounds and molecular materials. The site-selective C7-functionalization of these moieties has been proven to be extremely challenging due to the inherent reactivity of the C2- and C3-positions. Herein, we report the first electro-C7-alkenylation of indoles. This novel and sustainable methodology provides highly exclusive access to the C7-position devoid of often toxic and expensive chemical oxidants. Moreover, an array of substrates was successfully alkenylated at the C7-position, and versatile product diversification was achieved.
Truncated mucin-type O-glycans, such as Tn-associated antigens, are aberrantly expressed biomarkers of cancer, but remain challenging to target. Reactive antibodies to these antigens either lack high affinity or are prone to antigen escape. Here, we have developed a robust chemoenzymatic strategy for the global labeling of Tn-associated antigens, i. e. Tn (GalNAcα-O-Ser/Thr), Thomsen-Friedenreich (Galβ1-3GalNAcα-O-Ser/Thr, TF) and STF (Neu5Acα2-3Galβ1-3GalNAcα-O-Ser/Thr, STF) antigens, in human whole blood with high efficiency and selectivity. This method relies on the use of the O-glycan sialyltransferase ST6GalNAc1 to transfer a sialic acid-functionalized adaptor to the GalNAc residue of these antigens. By tagging, the adaptor functionalized antigens can be easily targeted by customized strategies such as, but not limited to, chimeric antigen receptor T-Cells (CAR-T). We expect this tagging system to find broad applications in cancer diagnostics and targeting in combination with established strategies.
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