Experimental Data SnapshotMethod: X-RAY DIFFRACTIONResolution: 1.82 ÅR-Value Free: 0.222 R-Value Work: 0.207 R-Value Observed: 0.208
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Characterization of the Structure & Function of Klebsiella pneumoniae Allantoin Racemase.French, J.B., Neau, D.B., Ealiông chồng, S.E.
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(2011) J Mol Biol 410: 447-460PubMed Abstract:
The oxidative catabolism of uric acid produces 5-hydroxyisourate (HIU), which is further degraded to lớn (S)-allantoin by two enzymes, HIU hydrolase và 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase. The intermediates of the latter two reactions, HIU and 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline, are unstable in solution and decay nonstereospecifically lớn allantoin ...
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The oxidative catabolism of uric acid produces 5-hydroxyisourate (HIU), which is further degraded khổng lồ (S)-allantoin by two enzymes, HIU hydrolase and 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase. The intermediates of the latter two reactions, HIU và 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline, are unstable in solution và decay nonstereospecifically lớn allantoin. In addition, nonenzymatic racemization of allantoin has been shown to lớn occur at physiological pH. Since the further breakdown of allantoin is catalyzed by allantoinase, an enzyme that is specific for (S)-allantoin, an allantoin racemase is necessary for complete & efficient catabolism of uric acid. In this work, we characterize the structure and activity of allantoin racemase from Klebsiella pneumoniae (KpHpxA). In addition lớn an unliganded structure solved using selenomethionyl single-wavelength anomalous dispersion, structures of C79S/C184S KpHpxA in complex with allantoin & with 5-acetylhydantoin are presented. These structures reveal several important features of the active sầu site including an oxyanion hole and a polar binding pocket that interacts with the ureivì tail of allantoin & serves to control the orientation of the hydantoin ring. The ability of KpHpxA to interconvert the (R)- & (S)-enantiomers of allantoin is demonstrated, & analysis of the steady-state kinetics of KpHpxA yielded a k(cat)/K(m) of 6.0 × 10(5) M(-1) s(-1). Mutation of either of the active-site cysteines, Cys79 or Cys184, khổng lồ serine inactivates this enzyme. The data presented provide new insights into the activity & substrate specificity of this enzyme và enable us khổng lồ propose a mechanism for catalysis that is consistent with the two-base mechanism observed in other members of the aspartate/glutamate family.
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Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA.
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