Sandbox Reserved 342: Difference between revisions
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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= | ||
XGPRT is a tetramer and the subunits are arranged so three of the four subunits contribute residues to each of the four active sites in the tetramer, which is why tetramers are required for protein function<ref name="Vos"/>. XGTPase has a conserved sequence,85-IVIDDLVDTG-94, which is called the PRib-PP (5-phospho-a-D-ribosyl-1-pyrophosphate)<scene name='Sandbox_Reserved_342/Prib-pp_binding_site/ | XGPRT is a tetramer and the subunits are arranged so three of the four subunits contribute residues to each of the four active sites in the tetramer, which is why tetramers are required for protein function<ref name="Vos"/>. XGTPase has a conserved sequence,85-IVIDDLVDTG-94, which is called the PRib-PP (5-phospho-a-D-ribosyl-1-pyrophosphate)<scene name='Sandbox_Reserved_342/Prib-pp_binding_site/3'>Binding site</scene>(The binding sites of each subunit is shown in pink). 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 loop, which is involved in substrate recognition<ref name="Vos"/>. | ||
=Function= | =Function= | ||
XGPRT is an enzyme that catalyzes the conversion of guanine, xanthine, and sometimes hypoxanthine, to GMP, XMP, and IMP <ref name="Vos"/>. This enzyme is part of the purine salvage pathway, which converts exogenous purines (bases or nucleosides) to nucleotides. | XGPRT is an enzyme that catalyzes the conversion of guanine, xanthine, and sometimes hypoxanthine, to GMP, XMP, and IMP <ref name="Vos"/>. This enzyme is part of the purine salvage pathway, which converts exogenous purines (bases or nucleosides) to nucleotides. | ||
<scene name='Sandbox_Reserved_342/Ligands/1'>Ligands</scene> | <scene name='Sandbox_Reserved_342/Ligands/1'>Ligands</scene> | ||
=Mechanism and Catalysis= | =Mechanism and Catalysis= | ||
<Structure load='1a96' size='300' frame='true' align='right' caption='Insert caption here' scene='Insert optional scene name here' /> | |||
In the large mobile loop of the XGPRT, there are several residues that are critical for substrate binding and catalysis<ref name="Vos"/>. The loop required for binding and catalysis is flexible, when XGPRT does not have products or substrates bound to it<ref name="Vos"/>. The flexibility of the residues in this loop assists movement of the loop towards the active site<ref name="Vos"/>. | In the large mobile loop of the XGPRT, there are several residues that are critical for substrate binding and catalysis<ref name="Vos"/>. The loop required for binding and catalysis is flexible, when XGPRT does not have products or substrates bound to it<ref name="Vos"/>. The flexibility of the residues in this loop assists movement of the loop towards the active site<ref name="Vos"/>. | ||
Revision as of 03:40, 4 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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| 1a96, resolution 2.00Å () | |||||||||
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| Ligands: | , , , | ||||||||
| Gene: | GPT (Escherichia coli) | ||||||||
| Activity: | Xanthine phosphoribosyltransferase, with EC number 2.4.2.22 | ||||||||
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| Resources: | FirstGlance, OCA, RCSB, PDBsum | ||||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||||
XANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASEXANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE
IntroductionIntroduction
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]
StructureStructure
XGPRT is a tetramer and the subunits are arranged so three of the four subunits contribute residues to each of the four active sites in the tetramer, which is why tetramers are required for protein function[1]. 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[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 loop, which is involved in substrate recognition[1].
FunctionFunction
XGPRT is an enzyme that catalyzes the conversion of guanine, xanthine, and sometimes hypoxanthine, to GMP, XMP, and IMP [1]. This enzyme is part of the purine salvage pathway, which converts exogenous purines (bases or nucleosides) to nucleotides.
Mechanism and CatalysisMechanism and Catalysis
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In the large mobile loop of the XGPRT, there are several residues that are critical for substrate binding and catalysis[1]. The loop required for binding and catalysis is flexible, when XGPRT does not have products or substrates bound to it[1]. The flexibility of the residues in this loop assists movement of the loop towards the active site[1].
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].
ReferencesReferences
- ↑ 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