pcr-mutagenesis-cloning-expression-fast-protein-purification

PCR Mutagenesis, Cloning, Expression, Fast Protein Purification Protocols and Crystallization of the Wild Type and Mutant Forms of Tryptophan Synthase

Structural studies with tryptophan synthase (TS) bienzyme complex (&#945;2&#946;2 TS) from Salmonella typhimurium have been performed to better understand ...

University of California-Riverside

Xanthomonas citri pv. citri (Xac) causes citrus canker and affects citrus agriculture worldwide. Functional genetic analysis has indicated that a putative general stress protein (XacGSP) encoded by the Xac2369 gene is involved in the bacterial infection. In this report, the crystal structure of XacGSP was determined to 2.5 Å resolution. There are four XacGSP molecules in the crystal asymmetric unit. Each XacGSP monomer folds into a six-stranded antiparallel β-barrel flanked by five α-helices. A C-terminal extension protrudes from the sixth β-strand of the β-barrel and pairs with its counterpart from another monomer to form a bridge between the two subunits of an XacGSP dimer. Two XacGSP dimers cross over each other to form a tetramer; the β-barrels from one dimer contact the β-barrels of the other, while the two bridges are distant from each other and do not make contacts. The three-dimensional structure of the XacGSP monomer is very similar to those of pyridoxine 5-phosphate oxidases, a group of enzymes that use flavin mononucleotide (FMN) as a cofactor. Consistent with this, purified XacGSP protein binds to both FMN and flavin adenine dinucleotide (FAD), suggesting that XacGSP may help the bacteria to react against the oxidative stress induced by the defense mechanisms of the plant.

The structure of a Xanthomonas general stress protein involved in citrus canker reveals its flavin-binding property.

Backbone assignments for the isolated α-subunit of Salmonella typhimurium tryptophan synthase (TS) are reported based on triple resonance solution-state NMR experiments on a uniformly H,C,N-labeled sample. From the backbone chemical shifts, secondary structure and random coil index order parameters (RCI-S) are predicted. Titration with the 3-indole-D-glycerol 3'-phosphate analog, N-(4'-trifluoromethoxybenzenesulfonyl)-2-aminoethyl phosphate (F9), leads to chemical shift perturbations indicative of conformational changes from which an estimate of the dissociation constant is obtained. Comparisons of the backbone chemical-shifts, RCI-S values, and site-specific relaxation times with and without F9 reveal allosteric changes including modulation in secondary structures and loop rigidity induced upon ligand binding. A comparison is made to the X-ray crystal structure of the α-subunit in the full TS αββα bi-enzyme complex and to two new X-ray crystal structures of the isolated TS α-subunit reported in this work.

Backbone assignments and conformational dynamics in the S. typhimurium tryptophan synthase α-subunit from solution-state NMR.

The genus Xanthomonas comprises several cosmopolitan plant-pathogenic bacteria that affect more than 400 plant species, most of which are of economic interest. Citrus canker is a bacterial disease that affects citrus species, reducing fruit yield and quality, and is caused by the bacterium Xanthomonas citri subsp. citri (Xac). The Xac3819 gene, which has previously been reported to be important for citrus canker infection, encodes an uncharacterized glutathione S-transferase (GST) of 207 amino-acid residues in length (XacGST). Bacterial GSTs are implicated in a variety of metabolic processes such as protection against chemical and oxidative stresses. XacGST shares high sequence identity (45%) with the GstB dehalogenase from Escherichia coli O6:H1 strain CFT073 (EcGstB). Here, XacGST is reported to be able to conjugate glutathione (GSH) with bromoacetate with a K of 6.67 ± 0.77 mM, a k of 42.69 ± 0.32 s and a k/K of 6.40 ± 0.72 mM s under a saturated GSH concentration (3.6 mM). These values are comparable to those previously reported for EcGstB. In addition, crystal structures of XacGST were determined in the apo form (PDB entry 6nxv) and in a GSH-bound complex (PDB entry 6nv6). XacGST has a canonical GST-like fold with a conserved serine residue (Ser12) at the GSH-binding site near the N-terminus, indicating XacGST to be a serine-type GST that probably belongs to the theta-class GSTs. GSH binding stabilizes a loop of about 20 residues containing a helix that is disordered in the apo XacGST structure.

Article	Year
The structure of a Xanthomonas general stress protein involved in citrus canker reveals its flavin-binding property. Acta crystallographica. Section D, Biological crystallography\| PubMed ID: 22751670	2012
Backbone assignments and conformational dynamics in the S. typhimurium tryptophan synthase α-subunit from solution-state NMR. Journal of biomolecular NMR\| PubMed ID: 32415580	2020
Structural and biochemical characterization of a glutathione transferase from the citrus canker pathogen Xanthomonas. Acta crystallographica. Section D, Structural biology\| PubMed ID: 32744260	2020

Eduardo Hilario

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