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.

High-Contrast and Fast-Removable 19 F-MRI Labels with Perfluoro-tert-Butyl Substituents.

19 F MRI is a unique technique for tracking and quantifying the indicator (19 F-MRI label) in vivo without the use of ionizing radiation. Here we report new 19 F-MRI labels, which are compounds with perfluoro-tert-butyl groups: 1,2-bis(perfluoro-tert-butoxy)ethane (C10 F18 H4 O2 ) and 1,3-bis(perfluoro-tert-butyl)propane (C11 F18 H6 ). Both substances contain 18 equivalent 19 F atoms, constituting 68.67 % and 71.25 % of the molecule, respectively. The emulsions with 19 F molecules were prepared and used in 19 F MRI studies in laboratory rats in vivo. The substances demonstrated high contrast properties, good biological inertness and the ability to be rapidly eliminated from the body. We showed that at a dose of 0.34 mg/g of body weight in rats, the time for complete elimination of C10 F18 H4 O2 and C11 F18 H6 is ∼30 days. The results turned out to be promising for the use of the presented compounds in 19 F MRI applications, especially since they are quite easy to synthesize.