Direct transfer of extended groups from synthetic cofactors by DNA methyltransferases

S-Adenosyl-L-methionine (AdoMet) is the major methyl donor for biological methylation reactions catalyzed by methyltransferases. We report the first chemical synthesis of AdoMet analogs with extended carbon chains replacing the methyl group and their evaluation as cofactors for all three classes of DNA methyltransferases. Extended groups containing a double or triple bond in the beta position to the sulfonium center were transferred onto DNA in a catalytic and sequence-specific manner, demonstrating a high utility of such synthetic cofactors for targeted functionalization of biopolymers.     

Rapid and synchronous chemical induction of replicative-like senescence via a small molecule inhibitor

Cellular senescence is acknowledged as a key contributor to organismal ageing and late-life disease. Though popular, the study of senescence in vitro can be complicated by the prolonged and asynchronous timing of cells committing to it and by its paracrine effects. To address these issues, we repurposed a small molecule inhibitor, inflachromene (ICM), to induce senescence to human primary cells. Within 6 days of treatment with ICM, senescence hallmarks, including the nuclear eviction of HMGB1 and -B2, are uniformly induced across IMR90 cell populations. By generating and comparing various high throughput datasets from ICM-induced and replicative senescence, we uncovered a high similarity of the two states. Notably though, ICM suppresses the pro-inflammatory secretome associated with senescence, thus alleviating most paracrine effects. In summary, ICM rapidly and synchronously induces a senescent-like phenotype thereby allowing the study of its core regulatory program without confounding heterogeneity.     

Synthesis of S-adenosyl-L-methionine analogs and their use for sequence-specific transalkylation of DNA by methyltransferases

Here we describe a one-step synthetic procedure for the preparation of S-adenosyl-L-methionine (AdoMet) analogs with extended carbon chains replacing the methyl group. These AdoMet analogs function as efficient cofactors for DNA methyltransferases (MTases), and we provide a protocol for sequence-specific transfer of extended side chains from these AdoMet analogs to DNA by DNA MTases. Direct chemoselective allylation or propargylation of S-adenosyl-L-homocysteine (AdoHcy) at sulfur is achieved under the acidic conditions needed to protect other nucleophilic positions in AdoHcy. The unsaturated bonds in beta position to the sulfonium center of the resulting AdoMet analogs are designed to stabilize the transition state formed upon DNA MTase-catalyzed nucleophilic attack at the carbon next to the sulfonium center and lead to efficient transfer of the extended side chains to DNA. Using these protocols, sequence-specific functionalized DNA can be obtained within one to two weeks.