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== '''XANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE''' ==
== '''XANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE''' ==
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__TOC__
__TOC__
=Introduction=
=Introduction=
Xanthine-guanine Phosphoribosyltansferase (XGPRT) is one of three purine phosphoribosyltransferases (PRTases) that are part of the purine salvage pathway in Escherichia coli<ref name="Vos"> PMID:9743633 </ref>; the other two PRTases in the pathway are HPRT and APRT<ref name="Vos"/>
Xanthine-guanine Phosphoribosyltansferase (XGPRT) is one of three purine phosphoribosyltransferases (PRTases) that are part of the purine salvage pathway in Escherichia coli<ref name="Vos"> PMID:9743633 </ref>; the other two PRTases in the pathway are HPRT and APRT<ref name="Vos"/>
=Structure=
=Structure=
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XGPRT is a tetramer<ref name="Vos"/>.
PRTase structures fall into two groups, type I and Type II<ref name="Vos"/>.
PRTase structures fall into two groups, type I and Type II<ref name="Vos"/>.
XGTPase has a conserved sequence,<scene name='Sandbox_Reserved_342/Prib-pp_binding_site/1'>85-IVIDDLVDTG-94</scene>, which is called the PRib-PP (5-phospho-a-D-ribosyl-1-pyrophosphate) binding site<ref name="Vos"/>. This binding site features two adjacent acidic residues, which are surrounded by hydrophobic residues<ref name="Vos"/>. 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<ref name="Vos"/>. Another region of the sequence in XGTPase forms a lobe, which is involved in substrate recognition<ref name="Vos"/>.
XGTPase has a conserved sequence,<scene name='Sandbox_Reserved_342/Prib-pp_binding_site/1'>85-IVIDDLVDTG-94</scene>, which is called the PRib-PP (5-phospho-a-D-ribosyl-1-pyrophosphate) binding site<ref name="Vos"/>. This binding site features two adjacent acidic residues, which are surrounded by hydrophobic residues<ref name="Vos"/>. 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<ref name="Vos"/>. Another region of the sequence in XGTPase forms a lobe, which is involved in substrate recognition<ref name="Vos"/>.
=Function=
=Function=
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XGRT is an enzyme that catalyzes the conversion of guanine, xanthine, and sometimes hypoxanthine, to GMP, XMP, and IMP <ref name="Vos"/>.
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XGPRT is an enzyme that catalyzes the conversion of guanine, xanthine, and sometimes hypoxanthine, to GMP, XMP, and IMP <ref name="Vos"/>.
<Structure load='1a96' size='300' frame='true' align='right' caption='Insert caption here' scene='Insert optional scene name here' />
<Structure load='1a96' size='300' frame='true' align='right' caption='Insert caption here' scene='Insert optional scene name here' />
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=MECHANISM=
=MECHANISM=
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In the large mobile loop of the XGRT, there are several residues that are critical for substrate binding and catalysis<ref name="Vos"/>.
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In the large mobile loop of the XGPRT, there are several residues that are critical for substrate binding and catalysis<ref name="Vos"/>.
==Recognition==
==Recognition==
==Catalysis==
==Catalysis==
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Magnesium and other divalent cations are necessary for catalysis<ref name="Vos"/>.
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Magnesium and other divalent cations are necessary for catalysis because magnesium and PRib-PP binding play a critical role for the PRTase reaction<ref name="Vos"/>. The Mg:PRib-PP complex binds to the active site of PRTases<ref name="Vos"/>. In type I PRTases, XGPRT, catalysis proceeds via SN1 mechanism and it forms a oxocarbonium ion in the transition state<ref name="Vos"/>. It has been suggested, that the magnesium ion departs with the displaced pyrophosphate because there is no magnesium ion at the active site<ref name="Vos"/>.
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=References=
=References=
<references/>
<references/>

Revision as of 02:53, 3 April 2011

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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PDB ID 1a96

Drag the structure with the mouse to rotate
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




XANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE

Contents

Introduction

Xanthine-guanine Phosphoribosyltansferase (XGPRT) is one of three purine phosphoribosyltransferases (PRTases) that are part of the purine salvage pathway in Escherichia coli[1]; the other two PRTases in the pathway are HPRT and APRT[1]

Structure

XGPRT is a tetramer[1]. PRTase structures fall into two groups, type I and Type II[1]. XGTPase has a conserved sequence,, which is called the PRib-PP (5-phospho-a-D-ribosyl-1-pyrophosphate) binding site[1]. This binding site features two adjacent acidic residues, which are surrounded by hydrophobic residues[1]. 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[1]. Another region of the sequence in XGTPase forms a lobe, which is involved in substrate recognition[1].

Function

XGPRT is an enzyme that catalyzes the conversion of guanine, xanthine, and sometimes hypoxanthine, to GMP, XMP, and IMP [1].

Insert caption here

Drag the structure with the mouse to rotate


MECHANISM

In the large mobile loop of the XGPRT, there are several residues that are critical for substrate binding and catalysis[1].

Recognition

Catalysis

Magnesium and other divalent cations are necessary for catalysis because magnesium and PRib-PP binding play a critical role for the PRTase reaction[1]. The Mg:PRib-PP complex binds to the active site of PRTases[1]. In type I PRTases, XGPRT, catalysis proceeds via SN1 mechanism and it forms a oxocarbonium ion in the transition state[1]. It has been suggested, that the magnesium ion departs with the displaced pyrophosphate because there is no magnesium ion at the active site[1].

References

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 Vos S, Parry RJ, Burns MR, de Jersey J, Martin JL. Structures of free and complexed forms of Escherichia coli xanthine-guanine phosphoribosyltransferase. J Mol Biol. 1998 Oct 2;282(4):875-89. PMID:9743633 doi:10.1006/jmbi.1998.2051
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