Sennoside A (SA), a typical prodrug, exerts its laxative effect only after its transformation into rheinanthrone catalyzed by gut microbial hydrolases and reductases. Hydrolases have been identified, but reductases remain unknown. By linking a photoreactive group to the SA scaffold, we synthesized a photoaffinity probe to covalently label SA reductases and identified SA reductases using activity-based protein profiling. From lysates of an active strain, Bifidobacterium pseudocatenulatum ( B . pseudocatenulatum ), 397 proteins were enriched and subsequently identified using mass spectrometry. Among these proteins, chromate reductase/nicotinamide adenine dinucleotide phosphate (NADPH)-dependent flavin mononucleotide (FMN) reductase/oxygen-insensitive NADPH nitroreductase (nfrA) was identified as a potent SA reductase through further bioinformatic analysis and Uniprot database screening. We also determined that recombinant nfrA could reduce SA. Our study contributes to further illuminating mechanisms of SA transformation to rheinanthrone and simultaneously offers an effective method to identify gut bacterial reductases.
Chong Liu,Fang Cheng,Bo Liu,Dongdong Gao,Gang Cheng,Chunmei Li,Huanan Wang,Wei He
Surface-initiated polymerization is an attractive approach to achieve desired interfacial compositions and properties on a wide range of substrates and surfaces. Due to mild reaction conditions, multiple surface-initiated polymerization methods, such as atom-transfer radical polymerization (ATRP), reversible addition–fragmentation chain-transfer polymerization, and so forth, have been developed and studied in academia and industry. However, the current methods require the combination of metal catalysts, special initiators, and oxygen removal. Herein, we developed a surface-initiated carbanion-mediated anionic polymerization (SI-CMAP), which can be conducted in aqueous solutions in the presence of oxygen without the need for metal catalysts. Zwitterionic 2-(N-3-sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate (SBMA) was selected as a model monomer to develop and demonstrate this strategy. The vinyl sulfone (VS) groups displayed on substrate surfaces reacted with N-methylimidazole (NMIM), which was used as the in situ initiator. The polymerization mechanism was extensively studied from many aspects at room temperature, including the changes in reaction conditions, factors affecting the polymerization extent, and substrate surfaces. We also demonstrated the compatibility of this method with a broad spectrum of monomers ranging from SBMA to other acrylates and acrylamides by using glycine betaine as a reaction additive. This method was also evaluated for the preparation of polymer-coated nanoparticles. For polymer-coated silica nanoparticles, their hydrodynamic diameter, copper contamination, and effects of salt and protein concentrations were compared with SI-ATRP in parallel. SI-CMAP in aqueous solutions in air and the absence of metal catalysts make this method sustainable and cost-effective. We believe that SI-CMAP can be readily adapted to the industrial surface coating and large-scale nanoparticle preparation under mild conditions.
危险品化学品经营许可证（带存储）