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Prokaryotic transcription factors (TFs) regulate gene expression in response to small molecules, thus representing promising candidates as versatile small molecule‐detecting biosensors valuable for synthetic biology applications. The engineering of such biosensors requires thorough in vitro and in vivo characterization of TF ligand response as well as detailed molecular structure information. In this work, we functionally and structurally characterize the Pca regulon regulatory protein (PcaR) transcription factor belonging to the IclR transcription factor family. Here, we present in vitro functional analysis of the ligand profile of PcaR and the construction of genetic circuits for the characterization of PcaR as an in vivo biosensor in the model eukaryote Saccharomyces cerevisiae. We report the crystal structures of PcaR in the apo state and in complex with one of its ligands, succinate, which suggests the mechanism of dicarboxylic acid recognition by this transcription factor. This work contributes key structural and functional insights enabling the engineering of PcaR for dicarboxylic acid biosensors, in addition to providing more insights into the IclR family of regulators. [ABSTRACT FROM AUTHOR]

The genome of the thermophilic fungus S cytalidium thermophilum (strain CBS 625.91) harbours a wide range of genes involved in carbohydrate degradation, including three genes, abf62A, abf62B and abf62C, predicted to encode glycoside hydrolase family 62 ( GH62) enzymes. Transcriptome analysis showed that only abf62A and abf62C are actively expressed during growth on diverse substrates including straws from barley, alfalfa, triticale and canola. The abf62A and abf62C genes were expressed in E scherichia coli and the resulting recombinant proteins were characterized. Calcium-free crystal structures of Abf62C in apo and xylotriose bound forms were determined to 1.23 and 1.48 Å resolution respectively. Site-directed mutagenesis confirmed Asp55, Asp171 and Glu230 as catalytic triad residues, and revealed the critical role of non-catalytic residues Asp194, Trp229 and Tyr338 in positioning the scissile α- L-arabinofuranoside bond at the catalytic site. Further, the +2 R substrate-binding site residues Tyr168 and Asn339, as well as the +2 NR residue Tyr226, are involved in accommodating long-chain xylan polymers. Overall, our structural and functional analysis highlights characteristic differences between Abf62A and Abf62C, which represent divergent subgroups in the GH62 family. [ABSTRACT FROM AUTHOR]

Glucuronic acid (GlcAp) and/or methylglucuronic acid (MeGlcAp) decorate the major forms of xylan in hardwood and coniferous softwoods as well as many cereal grains. Accordingly, the complete utilization of glucuronoxylans or conversion to sugar precursors requires the action of main chain xylanases as well as -glucuronidases that release the α- (1→2)-linked (Me)GlcAp side groups. Herein, a family GH115 enzyme from the marine bacterium Saccharophagus degradans 2-40T, SdeAgu115A, demonstrated activity toward glucuronoxylan and oligomers thereof with preference toward MeGlcAp linked to internal xylopyranosyl residues. Unique biochemical characteristics of NaCl activation were also observed. The crystal structure of SdeAgu115A revealed a five-domain architecture, with an additional insertion C+ domain that had significant impact on the domain arrangement of SdeAgu115A monomer and its dimerization. The participation of domain C+ in substrate binding was supported by reduced substrate inhibition upon introducing W773A, W689A, and F696A substitutions within this domain. In addition to Asp-335, the catalytic essentiality of Glu-216 was revealed by site-specific mutagenesis. A primary sequence analysis suggested that the SdeAgu115A architecture is shared by more than half of GH115 members, thus defining a distinct archetype for GH115 enzymes. [ABSTRACT FROM AUTHOR]

The genome of the thermophilic fungus Scytalidium thermophilum (strain CBS 625.91) harbours a wide range of genes involved in carbohydrate degradation, including three genes, abf62A, abf62B and abf62C, predicted to encode glycoside hydrolase family 62 (GH62) enzymes. Transcriptome analysis showed that only abf62A and abf62C are actively expressed during growth on diverse substrates including straws from barley, alfalfa, triticale and canola. The abf62A and abf62C genes were expressed in Escherichia coli and the resulting recombinant proteins were characterized. Calcium-free crystal structures of Abf62C in apo and xylotriose bound forms were determined to 1.23 and 1.48 Å resolution respectively. Site-directed mutagenesis confirmed Asp55, Asp171 and Glu230 as catalytic triad residues, and revealed the critical role of non-catalytic residues Asp194, Trp229 and Tyr338 in positioning the scissile α-L-arabinofuranoside bond at the catalytic site. Further, the +2R substrate-binding site residues Tyr168 and Asn339, as well as the +2NR residue Tyr226, are involved in accommodating long-chain xylan polymers. Overall, our structural and functional analysis highlights characteristic differences between Abf62A and Abf62C, which represent divergent subgroups in the GH62 family., (© 2014 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.)

Background: The direct isolation of integron gene cassettes from cultivated and environmental microbial sources allows an assessment of the impact of the integron/gene cassette system on the emergence of new phenotypes, such as drug resistance or virulence. A structural approach is being exploited to investigate the modularity and function of novel integron gene cassettes., Methodology/principal Findings: We report the 1.8 Å crystal structure of Cass2, an integron-associated protein derived from an environmental V. cholerae. The structure defines a monomeric beta-barrel protein with a fold related to the effector-binding portion of AraC/XylS transcription activators. The closest homologs of Cass2 are multi-drug binding proteins, such as BmrR. Consistent with this, a binding pocket made up of hydrophobic residues and a single glutamate side chain is evident in Cass2, occupied in the crystal form by polyethylene glycol. Fluorescence assays demonstrate that Cass2 is capable of binding cationic drug compounds with submicromolar affinity. The Cass2 module possesses a protein interaction surface proximal to its drug-binding cavity with features homologous to those seen in multi-domain transcriptional regulators., Conclusions/significance: Genetic analysis identifies Cass2 to be representative of a larger family of independent effector-binding proteins associated with lateral gene transfer within Vibrio and closely-related species. We propose that the Cass2 family not only has capacity to form functional transcription regulator complexes, but represents possible evolutionary precursors to multi-domain regulators associated with cationic drug compounds.

We tested the general applicability of in situ proteolysis to form protein crystals suitable for structure determination by adding a protease (chymotrypsin or trypsin) digestion step to crystallization trials of 55 bacterial and 14 human proteins that had proven recalcitrant to our best efforts at crystallization or structure determination. This is a work in progress; so far we determined structures of 9 bacterial proteins and the human aminoimidazole ribonucleotide synthetase (AIRS) domain.