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1a96

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{{STRUCTURE_1a96| PDB=1a96 | SCENE= }}
{{STRUCTURE_1a96| PDB=1a96 | SCENE= }}
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'''XPRTASE FROM E. COLI WITH BOUND CPRPP AND XANTHINE'''
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===XPRTASE FROM E. COLI WITH BOUND CPRPP AND XANTHINE===
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==Overview==
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Structures of free, substrate-bound and product-bound forms of Escherichia coli xanthine-guanine phosphoribosyltransferase (XGPRT) have been determined by X-ray crystallography. These are compared with the previously determined structure of magnesium and sulphate-bound XPRT. The structure of free XGPRT at 2.25 A resolution confirms the flexibility of residues in and around a mobile loop identified in other PRTases and shows that the cis-peptide conformation of Arg37 at the active site is maintained in the absence of bound ligands. The structures of XGPRT complexed with the purine base substrates guanine or xanthine in combination with cPRib-PP, an analog of the second substrate PRib-PP, have been solved to 2.0 A resolution. In these two structures the disordered phosphate-binding loop of uncomplexed XGPRT becomes ordered through interactions with the 5'-phosphate group of cPRib-PP. The cyclopentane ring of cPRib-PP has the C3 exo pucker conformation, stabilised by the cPRib-PP-bound Mg2+. The purine base specificity of XGPRT appears to be due to water-mediated interactions between the 2-exocyclic groups of guanine or xanthine and side-chains of Glu136 and Asp140, as well as the main-chain oxygen atom of Ile135. Asp92, together with Lys115, could help stabilise the N7-protonated tautomer of the incoming base and could act as a general base to remove the proton from N7 when the nucleotide product is formed. The 2.6 A resolution structure of XGPRT complexed with product GMP is similar to the substrate-bound complexes. However, the ribose ring of GMP is rotated by approximately 24 degrees compared with the equivalent ring in cPRib-PP. This rotation results in the loss of all interactions between the ribosyl group and the enzyme in the product complex.
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{{ABSTRACT_PUBMED_9743633}}
==About this Structure==
==About this Structure==
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[[Category: Purine salvage enzyme]]
[[Category: Purine salvage enzyme]]
[[Category: Transferase]]
[[Category: Transferase]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 16:25:05 2008''

Revision as of 13:25, 30 June 2008

Image:1a96.png


PDB ID 1a96

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1a96, resolution 2.00Å ()
Ligands: , , ,
Gene: GPT (Escherichia coli)
Activity: Xanthine phosphoribosyltransferase, with EC number 2.4.2.22
Resources: FirstGlance, OCA, RCSB, PDBsum
Coordinates: save as pdb, mmCIF, xml



XPRTASE FROM E. COLI WITH BOUND CPRPP AND XANTHINE

Template:ABSTRACT PUBMED 9743633

About this Structure

1A96 is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.

Reference

Structures of free and complexed forms of Escherichia coli xanthine-guanine phosphoribosyltransferase., Vos S, Parry RJ, Burns MR, de Jersey J, Martin JL, J Mol Biol. 1998 Oct 2;282(4):875-89. PMID:9743633

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