Structural Basis of Selective Aromatic Pollutant Sensing by the Effector Binding Domain of MopR, an NtrC Family Transcriptional Regulator

Phenol and its derivatives are common pollutants that are present in industrial discharge and are major xenobiotics that lead to water pollution. To monitor as well as improve water quality, attempts have been made in the past to engineer bacterial <i>in vivo</i> biosensors. However, due to the paucity of structural information, there is insufficiency in gauging the factors that lead to high sensitivity and selectivity, thereby impeding development. Here, we present the crystal structure of the sensor domain of MopR (MopR^AB) from <i>Acinetobacter calcoaceticus</i> in complex with phenol and its derivatives to a maximum resolution of 2.5 Å. The structure reveals that the N-terminal residues 21–47 possess a unique fold, which are involved in stabilization of the biological dimer, and the central ligand binding domain belongs to the “nitric oxide signaling and golgi transport” fold, commonly present in eukaryotic proteins that bind long-chain fatty acids. In addition, MopR^AB nests a zinc atom within a novel zinc binding motif, crucial for maintaining structural integrity. We propose that this motif is crucial for orchestrated motions associated with the formation of the effector binding pocket. Our studies reveal that residues W134 and H106 play an important role in ligand binding and are the key selectivity determinants. Furthermore, comparative analysis of MopR with XylR and DmpR sensor domains enabled the design of a MopR binding pocket that is competent in binding DmpR-specific ligands. Collectively, these findings pave way towards development of specific/broad based biosensors, which can act as useful tools for detection of this class of pollutants

Synthetic Precursors for TCNQF₄^2– Compounds: Synthesis, Characterization, and Electrochemical Studies of (Pr₄N)₂TCNQF₄ and Li₂TCNQF₄

Careful control of the reaction stoichiometry and conditions enables the synthesis of both LiTCNQF₄ and Li₂TCNQF₄ to be achieved. Reaction of LiI with TCNQF₄, in a 4:1 molar ratio, in boiling acetonitrile yields Li₂TCNQF₄. However, deviation from this ratio or the reaction temperature gives either LiTCNQF₄ or a mixture of Li₂TCNQF₄ and LiTCNQF₄. This is the first report of the large-scale chemical synthesis of Li₂TCNQF₄. Attempts to prepare a single crystal of Li₂TCNQF₄ have been unsuccessful, although air-stable (Pr₄N)₂TCNQF₄ was obtained by mixing Pr₄NBr with Li₂TCNQF₄ in aqueous solution. Pr₄NTCNQF₄ was also obtained by reaction of LiTCNQF₄ with Pr₄NBr in water. Li₂TCNQF₄, (Pr₄N)₂TCNQF₄, and Pr₄NTCNQF₄ have been characterized by UV–vis, FT-IR, Raman, and NMR spectroscopy, high resolution electrospray ionization mass spectrometry, and electrochemistry. The structures of single crystals of (Pr₄N)₂TCNQF₄ and Pr₄NTCNQF₄ have been determined by X-ray crystallography. These TCNQF₄^2– salts will provide useful precursors for the synthesis of derivatives of the dianions

Synthetic Precursors for TCNQF₄^2– Compounds: Synthesis, Characterization, and Electrochemical Studies of (Pr₄N)₂TCNQF₄ and Li₂TCNQF₄

Careful control of the reaction stoichiometry and conditions enables the synthesis of both LiTCNQF₄ and Li₂TCNQF₄ to be achieved. Reaction of LiI with TCNQF₄, in a 4:1 molar ratio, in boiling acetonitrile yields Li₂TCNQF₄. However, deviation from this ratio or the reaction temperature gives either LiTCNQF₄ or a mixture of Li₂TCNQF₄ and LiTCNQF₄. This is the first report of the large-scale chemical synthesis of Li₂TCNQF₄. Attempts to prepare a single crystal of Li₂TCNQF₄ have been unsuccessful, although air-stable (Pr₄N)₂TCNQF₄ was obtained by mixing Pr₄NBr with Li₂TCNQF₄ in aqueous solution. Pr₄NTCNQF₄ was also obtained by reaction of LiTCNQF₄ with Pr₄NBr in water. Li₂TCNQF₄, (Pr₄N)₂TCNQF₄, and Pr₄NTCNQF₄ have been characterized by UV–vis, FT-IR, Raman, and NMR spectroscopy, high resolution electrospray ionization mass spectrometry, and electrochemistry. The structures of single crystals of (Pr₄N)₂TCNQF₄ and Pr₄NTCNQF₄ have been determined by X-ray crystallography. These TCNQF₄^2– salts will provide useful precursors for the synthesis of derivatives of the dianions

Synthetic Precursors for TCNQF₄^2– Compounds: Synthesis, Characterization, and Electrochemical Studies of (Pr₄N)₂TCNQF₄ and Li₂TCNQF₄

Careful control of the reaction stoichiometry and conditions enables the synthesis of both LiTCNQF₄ and Li₂TCNQF₄ to be achieved. Reaction of LiI with TCNQF₄, in a 4:1 molar ratio, in boiling acetonitrile yields Li₂TCNQF₄. However, deviation from this ratio or the reaction temperature gives either LiTCNQF₄ or a mixture of Li₂TCNQF₄ and LiTCNQF₄. This is the first report of the large-scale chemical synthesis of Li₂TCNQF₄. Attempts to prepare a single crystal of Li₂TCNQF₄ have been unsuccessful, although air-stable (Pr₄N)₂TCNQF₄ was obtained by mixing Pr₄NBr with Li₂TCNQF₄ in aqueous solution. Pr₄NTCNQF₄ was also obtained by reaction of LiTCNQF₄ with Pr₄NBr in water. Li₂TCNQF₄, (Pr₄N)₂TCNQF₄, and Pr₄NTCNQF₄ have been characterized by UV–vis, FT-IR, Raman, and NMR spectroscopy, high resolution electrospray ionization mass spectrometry, and electrochemistry. The structures of single crystals of (Pr₄N)₂TCNQF₄ and Pr₄NTCNQF₄ have been determined by X-ray crystallography. These TCNQF₄^2– salts will provide useful precursors for the synthesis of derivatives of the dianions