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| | {{STRUCTURE_1dqp| PDB=1dqp | SCENE= }} | | {{STRUCTURE_1dqp| PDB=1dqp | SCENE= }} |
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| - | '''CRYSTAL STRUCTURE OF GIARDIA GUANINE PHOSPHORIBOSYLTRANSFERASE COMPLEXED WITH IMMUCILLING'''
| + | ===CRYSTAL STRUCTURE OF GIARDIA GUANINE PHOSPHORIBOSYLTRANSFERASE COMPLEXED WITH IMMUCILLING=== |
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| - | ==Overview==
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| - | Giardia lamblia, the protozoan parasite responsible for giardiasis, requires purine salvage from its host for RNA and DNA synthesis. G. lamblia expresses an unusual purine phosphoribosyltransferase with a high specificity for guanine (GPRTase). The enzyme's sequence significantly diverges from those of related enzymes in other organisms. The transition state analogue immucillinGP is a powerful inhibitor of HGXPRTase from malaria [Li, C. M., et al. (1999) Nat. Struct. Biol. 6, 582-587] and is also a 10 nM inhibitor of G. lamblia GPRTase. Cocrystallization of GPRTase with immucillinGP led unexpectedly to a GPRTase.immucillinG binary complex with an open catalytic site loop. Diffusion of ligands into preformed crystals gave a GPRTase.immucillinGP.Mg(2+).pyrophosphate complex in which the open loop is stabilized by crystal contacts. G. lamblia GPRTase exhibits substantial structural differences from known purine phosphoribosyltransferases at positions remote from the catalytic site, but conserves most contacts to the bound inhibitor. The filled catalytic site with an open catalytic loop provides insight into ligand binding. One active site Mg(2+) ion is chelated to pyrophosphate, but the other is chelated to two conserved catalytic site carboxylates, suggesting a role for these amino acids. This arrangement of Mg(2+) and pyrophosphate has not been reported in purine phosphoribosyltransferases. ImmucillinG in the binary complex is anchored by its 9-deazaguanine group, and the iminoribitol is disordered. No Mg(2+) or pyrophosphate is detected; thus, the 5'-phosphoryl group is needed to immobilize the iminoribitol prior to magnesium pyrophosphate binding. Filling the catalytic site involves (1) binding the purine ring, (2) anchoring the 5'-phosphate to fix the ribosyl group, (3) binding the first Mg(2+) to Asp125 and Glu126 carboxyl groups and binding Mg(2+).pyrophosphate, and (4) closing the catalytic site loop and formation of bound (Mg(2+))(2). pyrophosphate prior to catalysis. Guanine specificity is provided by two peptide carbonyl oxygens hydrogen-bonded to the exocyclic amino group and a weak interaction to O6. Transition state formation involves N7 protonation by Asp129 acting as the general acid.
| + | The line below this paragraph, {{ABSTRACT_PUBMED_10841757}}, adds the Publication Abstract to the page |
| | + | (as it appears on PubMed at http://www.pubmed.gov), where 10841757 is the PubMed ID number. |
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| | + | {{ABSTRACT_PUBMED_10841757}} |
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| | ==About this Structure== | | ==About this Structure== |
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| | [[Category: Immucilling]] | | [[Category: Immucilling]] |
| | [[Category: Protein-inhibitor complex]] | | [[Category: Protein-inhibitor complex]] |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 14:09:45 2008'' | + | |
| | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 23:28:33 2008'' |
Revision as of 20:28, 30 June 2008
Template:STRUCTURE 1dqp
CRYSTAL STRUCTURE OF GIARDIA GUANINE PHOSPHORIBOSYLTRANSFERASE COMPLEXED WITH IMMUCILLING
Template:ABSTRACT PUBMED 10841757
About this Structure
1DQP is a Single protein structure of sequence from Giardia intestinalis. Full crystallographic information is available from OCA.
Reference
Crystal structures of Giardia lamblia guanine phosphoribosyltransferase at 1.75 A(,)., Shi W, Munagala NR, Wang CC, Li CM, Tyler PC, Furneaux RH, Grubmeyer C, Schramm VL, Almo SC, Biochemistry. 2000 Jun 13;39(23):6781-90. PMID:10841757
Page seeded by OCA on Mon Jun 30 23:28:33 2008
