PDBsum entry: 1g9s

Transferase

PDB id: 1g9s

Contents

Protein chains

169 a.a. *

Ligands

IMP

__N

Waters ×96

* Residue conservation analysis

PDB id:

1g9s

Name:

Transferase

Title:

Crystal structure of a complex between e.Coli hprt and imp

Structure:

Hypoxanthine phosphoribosyltransferase. Chain: a, b. Engineered: yes

Source:

Escherichia coli. Organism_taxid: 562. Gene: hpt. Expressed in: escherichia coli. Expression_system_taxid: 562.

Biol. unit:

Tetramer (from PDB file)

Resolution:

2.80Å R-factor: 0.201 R-free: 0.243

Authors:

L.W.Guddat,S.Vos,J.L.Martin,D.T.Keough,J.De Jersey

Key ref:

L.W.Guddat et al. (2002). Crystal structures of free, IMP-, and GMP-bound Escherichia coli hypoxanthine phosphoribosyltransferase. Protein Sci, 11, 1626-1638. PubMed id: 12070315 DOI: 10.1110/ps.0201002

Date:

27-Nov-00 Release date: 28-Aug-02

Protein chains

P0A9M2  (HPRT_ECOLI) -  Hypoxanthine phosphoribosyltransferase

Seq: 178 a.a.

Struc: 169 a.a.*

* PDB and UniProt seqs differ at 1 residue position (black cross)

Enzyme reactions

• Enzyme class: E.C.2.4.2.8 - Hypoxanthine phosphoribosyltransferase.
• Reaction: IMP + diphosphate = hypoxanthine + 5-phospho-alpha-D-ribose 1-diphosphate

IMP (Bound ligand (Het Group name = IMP) corresponds exactly) + diphosphate = hypoxanthine + 5-phospho-alpha-D-ribose 1-diphosphate

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

 Gene Ontology (GO) functional annotation 

• Cellular component: cytoplasm (1 term)
• Biological process: regulation of catalytic activity (4 terms)
• Biochemical function: guanine phosphoribosyltransferase activity (11 terms)

reference

DOI no: 10.1110/ps.0201002

Protein Sci 11:1626-1638 (2002)

PubMed id: 12070315

Crystal structures of free, IMP-, and GMP-bound Escherichia coli hypoxanthine phosphoribosyltransferase.

L.W.Guddat, S.Vos, J.L.Martin, D.T.Keough, J.de Jersey.

ABSTRACT

Crystal structures have been determined for free Escherichia coli hypoxanthine phosphoribosyltransferase (HPRT) (2.9 A resolution) and for the enzyme in complex with the reaction products, inosine 5'-monophosphate (IMP) and guanosine 5'-monophosphate (GMP) (2.8 A resolution). Of the known 6-oxopurine phosphoribosyltransferase (PRTase) structures, E. coli HPRT is most similar in structure to that of Tritrichomonas foetus HGXPRT, with a rmsd for 150 Calpha atoms of 1.0 A. Comparison of the free and product bound structures shows that the side chain of Phe156 and the polypeptide backbone in this vicinity move to bind IMP or GMP. A nonproline cis peptide bond, also found in some other 6-oxopurine PRTases, is observed between Leu46 and Arg47 in both the free and complexed structures. For catalysis to occur, the 6-oxopurine PRTases have a requirement for divalent metal ion, usually Mg(2+) in vivo. In the free structure, a Mg(2+) is coordinated to the side chains of Glu103 and Asp104. This interaction may be important for stabilization of the enzyme before catalysis. E. coli HPRT is unique among the known 6-oxopurine PRTases in that it exhibits a marked preference for hypoxanthine as substrate over both xanthine and guanine. The structures suggest that its substrate specificity is due to the modes of binding of the bases. In E. coli HPRT, the carbonyl oxygen of Asp163 would likely form a hydrogen bond with the 2-exocyclic nitrogen of guanine (in the HPRT-guanine-PRib-PP-Mg(2+) complex). However, hypoxanthine does not have a 2-exocyclic atom and the HPRT-IMP structure suggests that hypoxanthine is likely to occupy a different position in the purine-binding pocket.

Selected figure(s)

Figure 1.
Fig. 1. (A) Two orthogonal views of the structure of subunit A from the E. coli HPRT-GMP complex. The ß-strands, shown as direction arrows are yellow in the core domain and pink in the hood domain. The mobile loop, which includes residues 73-82, is not observed in the crystal structure. To complete the structure, a hypothetical mobile loop has been modeled in and depicted as white coil. The GMP molecule is drawn as solid spheres and the atoms colored green for carbon, blue for nitrogen, red for oxygen, and pink for phosphorous. (B) The structure of the E. coli HPRT-GMP tetramer viewed down the crystallographic twofold axes. (C) The active site of subunit A of E. coli HPRT. (Top) The IMP complex. (Middle) The GMP complex. (Bottom) Free enzyme showing bound water molecules (red) and Mg2+ (pink) as solid spheres.

Figure 4.
Fig. 4. Superposition of subunit A from the E. coli HPRT-IMP complex and subunit A from the free enzyme.

The above figures are reprinted by permission from the Protein Society: Protein Sci (2002, 11, 1626-1638) copyright 2002.

Figures were selected by an automated process.