Sandbox Reserved 342

This Sandbox is Reserved from January 10, 2010, through April 10, 2011 for use in BCMB 307-Proteins course taught by Andrea Gorrell at the University of Northern British Columbia, Prince George, BC, Canada.

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spinqualitylabelsall models PDB ID 1a96 Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image
1a96, resolution 2.00Å ()
Ligands:	, , ,
Gene:	GPT (Escherichia coli)
Activity:	Xanthine phosphoribosyltransferase, with EC number 2.4.2.22
Structural annotation: Resources: CATH : 1A96A00, 1A96B00, 1A96C00, 1A96D00 InterPro : Ipr002375, Ipr000836 Pfam : PF00156 SCOP : d1a96a_, d1a96b_, d1a96c_, d1a96d_ UniProt : P0A9M5
Functional annotation: Cellular component: cytoplasm Biological process: purine ribonucleoside salvage nucleoside metabolic process Molecular function: magnesium ion binding transferase activity protein binding xanthine phosphoribosyltransferase activity metal ion binding transferase activity, transferring glycosyl groups
Evolutionary conservation: Toggle Conservation Colors: Rows = identical sequences: Further Information: Caveats, Explanation, Complete Results at ConSurfDB
Resources:	FirstGlance, OCA, RCSB, PDBsum
Coordinates:	save as pdb, mmCIF, xml

IntroductionIntroduction

Xanthine-guanine Phosphoribosyltansferase (XGPRT) is one of three purine phosphoribosyltransferases (PRTases) that are part of the purine salvage pathway in Escherichia coli; the other two PRTases in the pathway are HPRT and APRT

StructureStructure

XGPRT is a tetramer. PRTase structures fall into two groups, type I and Type II. XGTPase has a conserved sequence,85-IVIDDLVDTG-94, which is called the PRib-PP (5-phospho-a-D-ribosyl-1-pyrophosphate)(The binding sites of each subunit is shown in pink). This binding site features two adjacent acidic residues, which are surrounded by hydrophobic residues. There is a five-stranded b-sheet surrounded by three or four a-helices that creates a conserved structural core containing the PRib-PP binding site. Another region of the sequence in XGTPase forms a lobe, which is involved in substrate recognition.

FunctionFunction

XGPRT is an enzyme that catalyzes the conversion of guanine, xanthine, and sometimes hypoxanthine, to GMP, XMP, and IMP .

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MechanismMechanism

In the large mobile loop of the XGPRT, there are several residues that are critical for substrate binding and catalysis.

CatalysisCatalysis

Magnesium and other divalent cations are necessary for catalysis because magnesium and PRib-PP binding play a critical role for the PRTase reaction. The Mg:PRib-PP complex binds to the active site of PRTases. In type I PRTases, XGPRT, catalysis proceeds via SN1 mechanism and it forms a oxocarbonium ion in the transition state. It has been suggested, that the magnesium ion departs with the displaced pyrophosphate because there is no magnesium ion at the active site.