The 2 2 angstrom resolution crystal structure of the G lamblia e

The 2.2 angstrom resolution crystal structure of the G. lamblia enzyme presented here is thus the first structure determination of a prolyl-tRNA synthetase from a eukaryote. The relative occupancies of substrate (proline) and product (prolyl-AMP) in the active site are consistent with half-of-the-sites reactivity, as is the observed biphasic CC-5013 thermal denaturation curve for the protein in the presence of proline and MgATP. However, no corresponding induced asymmetry is evident in the structure of the protein. No thermal stabilization is observed in the presence of cysteine and ATP. The Inhibitors,Modulators,Libraries implied low affinity for the off-target Inhibitors,Modulators,Libraries activation product cysteinyl-AMP suggests that translational fidelity in Giardia is aided by the rapid release of misactivated cysteine.

D-Xylose isomerase (XI) Inhibitors,Modulators,Libraries converts the aldo-sugars xylose and glucose to their keto analogs xylulose and fructose, but is strongly inhibited by the polyols xylitol and sorbitol, especially at acidic pH. In order to understand Inhibitors,Modulators,Libraries the atomic details of polyol binding to the XI active site, a 2.0 angstrom resolution roomtemperature joint X-ray/neutron structure of XI in complex with Ni2+ cofactors and sorbitol inhibitor at pH 5.9 and a room-temperature X-ray structure of XI containing Mg2+ ions and xylitol at the physiological pH of 7.7 were obtained. The protonation of oxygen O5 of the inhibitor, which was found to be deprotonated and negatively charged in previous structures of XI complexed with linear glucose and xylulose, was directly observed. The Ni2+ ions occupying the catalytic metal site (M2) were found at two locations, while Mg2+ in M2 is very mobile and has a high B factor.

Under acidic conditions sorbitol gains a water-mediated interaction that connects its O1 hydroxyl to Asp257. This contact is not found in structures at basic pH. The new interaction that is formed may improve the AV-951 binding of the inhibitor, providing an explanation for the increased affinity of the polyols for XI at low pH.
The structures of two mutants (H192A and Y246F) of a mannuronate-specific alginate lyase, A1-III, from Sphingomonas species A1 complexed with a tetrasaccharide CHIR99021 substrate [4-deoxy-l-erythro-hex-4-ene-pyranosyluronate-(mannuronate)(2)-mannuronic acid] were determined by X-ray crystallography at around 2.2 angstrom resolution together with the apo form of the H192A mutant. The final models of the complex forms, which comprised two monomers (of 353 amino-acid residues each), 268-287 water molecules and two tetrasaccharide substrates, had R factors of around 0.17. A large conformational change occurred in the position of the lid loop (residues 64-85) in holo H192A and Y246F compared with that in apo H192A.

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