2 research outputs found

    Crystal Structures of the F and pSLT Plasmid TraJ N‑Terminal Regions Reveal Similar Homodimeric PAS Folds with Functional Interchangeability

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    In the F family of conjugative plasmids, TraJ is an essential transcriptional activator of the <i>tra</i> operon that encodes most of the proteins required for conjugation. Here we report for the first time the X-ray crystal structures of the TraJ N-terminal domains from the prototypic F plasmid (TraJ<sub>F</sub><sup>11–130</sup>) and from the Salmonella virulence plasmid pSLT (TraJ<sub>pSLT</sub><sup>1–128</sup>). Both structures contain similar Per-ARNT-Sim (PAS) folds, which further homodimerize through the N-terminal helix and the structurally conserved β-sheet of the PAS fold from each protomer. Mutational analysis reveals that the observed dimeric interface is critical for TraJ<sub>F</sub> transcriptional activation, indicating that dimerization of TraJ is required for its <i>in vivo</i> function. TraJ is specific in activating its cognate <i>tra</i> operon promoter; however, heterologous PAS domains from pSLT and R100 TraJ can functionally replace the TraJ<sub>F</sub> PAS domain, suggesting that the allelic specificity of TraJ is solely mediated by the region C-terminal to the PAS domain

    <i>Bacillus anthracis</i> Inosine 5′-Monophosphate Dehydrogenase in Action: The First Bacterial Series of Structures of Phosphate Ion‑, Substrate‑, and Product-Bound Complexes

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    Inosine 5′-monophosphate dehydrogenase (IMPDH) catalyzes the first unique step of the GMP branch of the purine nucleotide biosynthetic pathway. This enzyme is found in organisms of all three kingdoms. IMPDH inhibitors have broad clinical applications in cancer treatment, as antiviral drugs and as immunosuppressants, and have also displayed antibiotic activity. We have determined three crystal structures of <i>Bacillus anthracis</i> IMPDH, in a phosphate ion-bound (termed “apo”) form and in complex with its substrate, inosine 5′-monophosphate (IMP), and product, xanthosine 5′-monophosphate (XMP). This is the first example of a bacterial IMPDH in more than one state from the same organism. Furthermore, for the first time for a prokaryotic enzyme, the entire active site flap, containing the conserved Arg-Tyr dyad, is clearly visible in the structure of the apoenzyme. Kinetic parameters for the enzymatic reaction were also determined, and the inhibitory effect of XMP and mycophenolic acid (MPA) has been studied. In addition, the inhibitory potential of two known <i>Cryptosporidium parvum</i> IMPDH inhibitors was examined for the <i>B. anthracis</i> enzyme and compared with those of three bacterial IMPDHs from <i>Campylobacter jejuni</i>, <i>Clostridium perfringens</i>, and <i>Vibrio cholerae</i>. The structures contribute to the characterization of the active site and design of inhibitors that specifically target <i>B. anthracis</i> and other microbial IMPDH enzymes
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