Organophosphorus S-adenosyl-L-methionine mimetics: synthesis, stability, and substrate properties.

S-Adenosyl-l-methionine (SAM)-mediated methylation of biomolecules controls their function and regulates numerous vital intracellular processes. Analogs of SAM with a reporter group in place of the S-methyl group are widely used to study these processes. However, many of these analogs are chemically unstable that largely limits their practical application. We have developed a new compound, SAM-P H , which contains an H-phosphinic group (-P(O)(H)OH) instead of the SAM carboxylic group. SAM-P H is significantly more stable than SAM, retains functional activity in catechol-O-methyltransferase and methyltransferase WBSCR27 reactions. The last is associated with Williams-Beuren syndrome. Rac-SAM-P H was synthesized chemically, while (R,S)-SAM-P H and its analogs were prepared enzymatically either from H-phosphinic analogs of methionine (Met-PH) or H-phosphinic analog of S-adenosyl-l-homocysteine (SAH-P H ) using methionine adenosyltransferase 2A or halide methyltransferases, respectively. SAH-P H undergoes glycoside bond cleavage in the presence of methylthioadenosine nucleosidase like natural SAH. Thus, SAM-P H and its analogs are promising new tools for investigating methyltransferases and incorporating reporter groups into their substrates.

Phylogeny and structural modeling of the transcription factor CsqR (YihW) from Escherichia coli.

CsqR (YihW) is a local transcription factor that controls expression of yih genes involved in degradation of sulfoquinovose in Escherichia coli. We recently showed that expression of the respective gene cassette might be regulated by lactose. Here, we explore the phylogenetic and functional traits of CsqR. Phylogenetic analysis revealed that CsqR had a conserved Met25. Western blot demonstrated that CsqR was synthesized in the bacterial cell as two protein forms, 28.5 (CsqR-l) and 26 kDa (CsqR-s), the latter corresponding to start of translation at Met25. CsqR-s was dramatically activated during growth with sulfoquinovose as a sole carbon source, and displaced CsqR-l in the stationary phase during growth on rich medium. Molecular dynamic simulations revealed two possible states of the CsqR-s structure, with the interdomain linker being represented by either a disordered loop or an ɑ-helix. This helix allowed the hinge-like motion of the N-terminal domain resulting in a switch of CsqR-s between two conformational states, "open" and "compact". We then modeled the interaction of both CsqR forms with putative effectors sulfoquinovose, sulforhamnose, sulfoquinovosyl glycerol, and lactose, and revealed that they all preferred the same pocket in CsqR-l, while in CsqR-s there were two possible options dependent on the linker structure.