Escherichia coli K-12 substr. MG1655 Enzyme: hypoxanthine phosphoribosyltransferase

Gene: hpt Accession Numbers: EG20098 (EcoCyc), b0125, ECK0124

Regulation Summary Diagram: ?

Regulation summary diagram for hpt

Subunit composition of hypoxanthine phosphoribosyltransferase = [Hpt]4
         hypoxanthine-guanine phosphoribosyltransferase = Hpt

Hypoxanthine phosphoribosyltransferase is a purine salvage enzyme whose primary activity is with hypoxanthine as the substrate [Guddat02]. The enzyme's activity with guanine appears to be sufficient to salvage guanine for guanine nucleotide synthesis [Jochimsen75, Holden76].

A V157A Y173H double mutant generated by directed evolution shows promiscuous substrate specificity [Scism07]. An initial report on purification of the enzyme found it to be membrane-associated, and substrate specificity appeared to be related to membrane localization [Hochstadt78a].

Crystal structures of free and product-bound forms of the enzyme have been solved [Guddat02].

Expression of hpt is negatively regulated by IHF and positively regulated by CRP, which is the opposite effect of the same regulators and binding sites on the divergently transcribed gcd [Izu02].

The amino acid sequence of E. coli Hpt shares only 23% identity with that of E. coli Gpt, despite their common function. It is more similar to human HGPRT, with 33% identity [Guddat02].

Locations: cytosol

Map Position: [141,431 -> 141,967] (3.05 centisomes, 11°)
Length: 537 bp / 178 aa

Molecular Weight of Polypeptide: 20.115 kD (from nucleotide sequence), 20.6 kD (experimental) [Guddat02 ]

Molecular Weight of Multimer: 79.0 kD (experimental) [Guddat02]

Unification Links: ASAP:ABE-0000440 , CGSC:622 , DIP:DIP-47994N , EchoBASE:EB4143 , EcoGene:EG20098 , EcoliWiki:b0125 , Entrez-gene:946624 , ModBase:P0A9M2 , OU-Microarray:b0125 , PortEco:hpt , PR:PRO_000022921 , Pride:P0A9M2 , Protein Model Portal:P0A9M2 , RefSeq:NP_414667 , RegulonDB:EG20098 , SMR:P0A9M2 , String:511145.b0125 , UniProt:P0A9M2

Relationship Links: InterPro:IN-FAMILY:IPR000836 , InterPro:IN-FAMILY:IPR005904 , InterPro:IN-FAMILY:IPR029057 , PDB:Structure:1G9S , PDB:Structure:1G9T , PDB:Structure:1GRV , Pfam:IN-FAMILY:PF00156 , Prosite:IN-FAMILY:PS00103

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Genetic Regulation Schematic: ?

Genetic regulation schematic for hpt

GO Terms:

Biological Process: GO:0032263 - GMP salvage Inferred from experiment [Guddat02, Jochimsen75]
GO:0032264 - IMP salvage Inferred from experiment Inferred by computational analysis [UniProtGOA12, Guddat02, Jochimsen75]
GO:0006166 - purine ribonucleoside salvage Inferred by computational analysis [UniProtGOA11, GOA01, Gaudet10]
GO:0006168 - adenine salvage Inferred by computational analysis [Gaudet10]
GO:0006178 - guanine salvage Inferred by computational analysis [Gaudet10]
GO:0009116 - nucleoside metabolic process Inferred by computational analysis [GOA01]
GO:0046100 - hypoxanthine metabolic process Inferred by computational analysis [Gaudet10]
Molecular Function: GO:0000287 - magnesium ion binding Inferred from experiment [Hochstadt78a]
GO:0004422 - hypoxanthine phosphoribosyltransferase activity Inferred from experiment Inferred by computational analysis [GOA01a, GOA01, Jochimsen75, Guddat02]
GO:0042802 - identical protein binding Inferred from experiment [Guddat02]
GO:0000166 - nucleotide binding Inferred by computational analysis [UniProtGOA11]
GO:0016740 - transferase activity Inferred by computational analysis [UniProtGOA11]
GO:0016757 - transferase activity, transferring glycosyl groups Inferred by computational analysis [UniProtGOA11]
GO:0046872 - metal ion binding Inferred by computational analysis [UniProtGOA11]
GO:0052657 - guanine phosphoribosyltransferase activity Inferred by computational analysis [GOA01a]
Cellular Component: GO:0005829 - cytosol Inferred from experiment Inferred by computational analysis [DiazMejia09, Ishihama08, LopezCampistrou05, Gaudet10, Page78]
GO:0005737 - cytoplasm Inferred by computational analysis [UniProtGOA11a, UniProtGOA11, GOA01]

MultiFun Terms: metabolism central intermediary metabolism nucleotide and nucleoside conversions

Essentiality data for hpt knockouts: ?

Growth Medium Growth? T (°C) O2 pH Osm/L Growth Observations
LB enriched Yes 37 Aerobic 6.95   Yes [Gerdes03, Comment 1]
LB Lennox Yes 37 Aerobic 7   Yes [Baba06, Comment 2]
M9 medium with 1% glycerol Yes 37 Aerobic 7.2 0.35 Yes [Joyce06, Comment 3]
MOPS medium with 0.4% glucose Yes 37 Aerobic 7.2 0.22 Yes [Baba06, Comment 2]
Yes [Feist07, Comment 4]

Created 21-Apr-2008 by Keseler I , SRI International
Curated 21-Apr-2008 by Keseler I , SRI International
Reviewed 11-Feb-2010 by Sarker M
Reviewed 16-Feb-2010 by Sarker M
Last-Curated ? 06-Dec-2011 by Fulcher C , SRI International

Enzymatic reaction of: guanine phosphoribosyltransferase (hypoxanthine phosphoribosyltransferase)

EC Number:

guanine + 5-phospho-α-D-ribose 1-diphosphate <=> GMP + diphosphate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction of enzyme catalysis.

The reaction is irreversible in the direction shown.

In Pathways: superpathway of guanine and guanosine salvage , guanine and guanosine salvage

Kinetic Parameters:

Km (μM)

Enzymatic reaction of: hypoxanthine phosphoribosyltransferase

Synonyms: IMP pyrophosphorylase, transphosphoribosidase, HPRT, IMP:pyrophosphate phospho-d-ribosyltransferase

EC Number:

5-phospho-α-D-ribose 1-diphosphate + hypoxanthine <=> IMP + diphosphate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction of enzyme catalysis.

The reaction is physiologically favored in the direction shown.

Alternative Substrates [Comment 5]:

In Pathways: adenine and adenosine salvage III

Cofactors or Prosthetic Groups [Hochstadt78a]: Mg2+ [Hochstadt78a]

Alternative Cofactors for Mg2+: Mn2+

Inhibitors (Unknown Mechanism): a 6-hydroxypurine nucleotide [Hochstadt78a] , GMP [Guddat02] , IMP [Hochstadt78a, Guddat02] , Ba2+ [Hochstadt78a] , Ca2+ [Hochstadt78a] , Zn2+ [Hochstadt78a] , ppGpp [Hochstadt78a]

Primary Physiological Regulators of Enzyme Activity: IMP , ppGpp

Kinetic Parameters:

Km (μM)
5-phospho-α-D-ribose 1-diphosphate

pH(opt): 8.4 [Hochstadt78a]

Sequence Features

Protein sequence of hypoxanthine-guanine phosphoribosyltransferase with features indicated

Feature Class Location Attached Group Citations Comment
Nucleotide-Phosphate-Binding-Region 99 -> 108 IMP
UniProt: IMP.
Active-Site 103  
UniProt: Proton acceptor; Non-Experimental Qualifier: probable.
Amino-Acid-Sites-That-Bind 131  
UniProt: IMP.
Amino-Acid-Sites-That-Bind 153  
UniProt: IMP; via carbonyl oxygen.
Nucleotide-Phosphate-Binding-Region 158 -> 159 IMP
UniProt: IMP.
Metal-Binding-Site 159  
UniProt: Magnesium 1; Non-Experimental Qualifier: by similarity;

Gene Local Context (not to scale): ?

Gene local context diagram

Transcription Units:

Transcription-unit diagram

Transcription-unit diagram

Transcription-unit diagram


Peter D. Karp on Wed Jan 18, 2006:
Gene left-end position adjusted based on analysis performed in the 2005 E. coli annotation update [Riley06 ].
10/20/97 Gene b0125 from Blattner lab Genbank (v. M52) entry merged into EcoCyc gene EG20098; confirmed by SwissProt match.


Baba06: Baba T, Ara T, Hasegawa M, Takai Y, Okumura Y, Baba M, Datsenko KA, Tomita M, Wanner BL, Mori H (2006). "Construction of Escherichia coli K-12 in-frame, single-gene knockout mutants: the Keio collection." Mol Syst Biol 2;2006.0008. PMID: 16738554

DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114

Feist07: Feist AM, Henry CS, Reed JL, Krummenacker M, Joyce AR, Karp PD, Broadbelt LJ, Hatzimanikatis V, Palsson BO (2007). "A genome-scale metabolic reconstruction for Escherichia coli K-12 MG1655 that accounts for 1260 ORFs and thermodynamic information." Mol Syst Biol 3;121. PMID: 17593909

Gaudet10: Gaudet P, Livstone M, Thomas P (2010). "Annotation inferences using phylogenetic trees." PMID: 19578431

Gerdes03: Gerdes SY, Scholle MD, Campbell JW, Balazsi G, Ravasz E, Daugherty MD, Somera AL, Kyrpides NC, Anderson I, Gelfand MS, Bhattacharya A, Kapatral V, D'Souza M, Baev MV, Grechkin Y, Mseeh F, Fonstein MY, Overbeek R, Barabasi AL, Oltvai ZN, Osterman AL (2003). "Experimental determination and system level analysis of essential genes in Escherichia coli MG1655." J Bacteriol 185(19);5673-84. PMID: 13129938

GOA01: GOA, DDB, FB, MGI, ZFIN (2001). "Gene Ontology annotation through association of InterPro records with GO terms."

GOA01a: GOA, MGI (2001). "Gene Ontology annotation based on Enzyme Commission mapping." Genomics 74;121-128.

Guddat02: Guddat LW, Vos S, Martin JL, Keough DT, de Jersey J (2002). "Crystal structures of free, IMP-, and GMP-bound Escherichia coli hypoxanthine phosphoribosyltransferase." Protein Sci 11(7);1626-38. PMID: 12070315

Hochstadt78a: Hochstadt J (1978). "Hypoxanthine phosphoribosyltransferase and guanine phosphoribosyltransferase from enteric bacteria." Methods Enzymol 1978;51;549-58. PMID: 692401

Holden76: Holden JA, Harriman PD, Wall JD (1976). "Escherichia coli mutants deficient in guanine-xanthine phosphoribosyltransferase." J Bacteriol 126(3);1141-8. PMID: 820683

Ishihama08: Ishihama Y, Schmidt T, Rappsilber J, Mann M, Hartl FU, Kerner MJ, Frishman D (2008). "Protein abundance profiling of the Escherichia coli cytosol." BMC Genomics 9;102. PMID: 18304323

Izu02: Izu H, Ito S, Elias MD, Yamada M (2002). "Differential control by IHF and cAMP of two oppositely oriented genes, hpt and gcd, in Escherichia coli: significance of their partially overlapping regulatory elements." Mol Genet Genomics 266(5);865-72. PMID: 11810262

Jochimsen75: Jochimsen B, Nygaard P, Vestergaard T (1975). "Location on the chromosome of Escherichia coli of genes governing purine metabolism. Adenosine deaminase (add), guanosine kinase (gsk) and hypoxanthine phosphoribosyltransferase (hpt)." Mol Gen Genet 1975;143(1);85-91. PMID: 765747

Joyce06: Joyce AR, Reed JL, White A, Edwards R, Osterman A, Baba T, Mori H, Lesely SA, Palsson BO, Agarwalla S (2006). "Experimental and computational assessment of conditionally essential genes in Escherichia coli." J Bacteriol 188(23);8259-71. PMID: 17012394

LopezCampistrou05: Lopez-Campistrous A, Semchuk P, Burke L, Palmer-Stone T, Brokx SJ, Broderick G, Bottorff D, Bolch S, Weiner JH, Ellison MJ (2005). "Localization, annotation, and comparison of the Escherichia coli K-12 proteome under two states of growth." Mol Cell Proteomics 4(8);1205-9. PMID: 15911532

Page78: Page MG, Burton K (1978). "The location of purine phosphoribosyltransferase activities in Escherichia coli." Biochem J 1978;174(3);717-25. PMID: 365172

Riley06: Riley M, Abe T, Arnaud MB, Berlyn MK, Blattner FR, Chaudhuri RR, Glasner JD, Horiuchi T, Keseler IM, Kosuge T, Mori H, Perna NT, Plunkett G, Rudd KE, Serres MH, Thomas GH, Thomson NR, Wishart D, Wanner BL (2006). "Escherichia coli K-12: a cooperatively developed annotation snapshot--2005." Nucleic Acids Res 34(1);1-9. PMID: 16397293

Scism07: Scism RA, Stec DF, Bachmann BO (2007). "Synthesis of nucleotide analogues by a promiscuous phosphoribosyltransferase." Org Lett 9(21);4179-82. PMID: 17854193

UniProt10: UniProt Consortium (2010). "UniProt version 2010-07 released on 2010-06-15 00:00:00." Database.

UniProt11: UniProt Consortium (2011). "UniProt version 2011-06 released on 2011-06-30 00:00:00." Database.

UniProt15: UniProt Consortium (2015). "UniProt version 2015-01 released on 2015-01-16 00:00:00." Database.

UniProtGOA11: UniProt-GOA (2011). "Gene Ontology annotation based on manual assignment of UniProtKB keywords in UniProtKB/Swiss-Prot entries."

UniProtGOA11a: UniProt-GOA (2011). "Gene Ontology annotation based on the manual assignment of UniProtKB Subcellular Location terms in UniProtKB/Swiss-Prot entries."

UniProtGOA12: UniProt-GOA (2012). "Gene Ontology annotation based on UniPathway vocabulary mapping."

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Please cite the following article in publications resulting from the use of EcoCyc: Nucleic Acids Research 41:D605-12 2013
Page generated by SRI International Pathway Tools version 19.0 on Mon Mar 30, 2015, BIOCYC14B.