1djo
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(New page: 200px<br /><applet load="1djo" size="450" color="white" frame="true" align="right" spinBox="true" caption="1djo, resolution 2.00Å" /> '''CRYSTAL STRUCTURE OF...)
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Revision as of 11:13, 20 November 2007
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CRYSTAL STRUCTURE OF PSEUDOMONAS 7A GLUTAMINASE-ASPARAGINASE WITH THE INHIBITOR DONV COVALENTLY BOUND IN THE ACTIVE SITE
Overview
Pseudomonas 7A glutaminase-asparaginase (PGA) catalyzes the hydrolysis of, D and L isomers of glutamine and asparagine. Crystals of PGA were reacted, with diazo analogues of glutamine (6-diazo-5-oxo-L-norleucine, DON) and, asparagine (5-diazo-4-oxo-L-norvaline, DONV), which are known inhibitors, of the enzyme. The derivatized crystals remained isomorphous to native PGA, crystals. Their structures were refined to crystallographic R = 0.20 and, R(free) = 0.24 for PGA-DON and R = 0.19 and R = 0.23 for PGA-DONV., Difference Fourier electron density maps clearly showed that both DON and, DONV inactivate PGA through covalent inhibition. Continuous electron, density connecting the inhibitor to both Thr20 and Tyr34 of the flexible, loop was observed providing strong evidence that Thr20 is the primary, catalytic nucleophile and that Tyr34 plays an important role in catalysis, as well. The unexpected covalent binding observed in the PGA-DON and, PGA-DONV complexes shows that a secondary reaction involving the formation, of a Tyr34-inhibitor bond takes place with concomitant inactivation of, PGA. The predicted covalent linkage is not seen, however, suggesting an, alternative method of inhibition not yet seen for these diazo analogues., These surprising results give insight as to the role of the flexible loop, Thr and Tyr in the catalytic mechanism.
About this Structure
1DJO is a Single protein structure of sequence from Pseudomonas sp. with CAB as ligand. Active as Glutamin-(asparagin-)ase, with EC number 3.5.1.38 Full crystallographic information is available from OCA.
Reference
Reactions of Pseudomonas 7A glutaminase-asparaginase with diazo analogues of glutamine and asparagine result in unexpected covalent inhibitions and suggests an unusual catalytic triad Thr-Tyr-Glu., Ortlund E, Lacount MW, Lewinski K, Lebioda L, Biochemistry. 2000 Feb 15;39(6):1199-204. PMID:10684596
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