2OAT

ORNITHINE AMINOTRANSFERASE COMPLEXED WITH 5-FLUOROMETHYLORNITHINE

Summary for 2OAT

• Entry DOI: 10.2210/pdb2oat/pdb
• Descriptor: ORNITHINE AMINOTRANSFERASE, 1-AMINO-7-(2-METHYL-3-OXIDO-5-((PHOSPHONOXY)METHYL)-4-PYRIDOXAL-5-OXO-6-HEPTENATE (3 entities in total)
• Functional Keywords: aminotransferase, 5-fluoromethylornithine, plp-dependent enzyme, pyridoxal phosphate
• Biological source: Homo sapiens (human)
• Cellular location: Mitochondrion matrix: P04181
• Total number of polymer chains: 3
• Total formula weight: 146903.85

Authors

Storici, P.,Schirmer, T. (deposition date: 1998-05-07, release date: 1998-12-09, Last modification date: 2024-05-22)

Primary citation

Storici, P.,Capitani, G.,Muller, R.,Schirmer, T.,Jansonius, J.N.
Crystal structure of human ornithine aminotransferase complexed with the highly specific and potent inhibitor 5-fluoromethylornithine.
J.Mol.Biol., 285:297-309, 1999

PubMed Abstract: Ornithine aminotransferase (l-ornithine:2-oxoacid delta-aminotransferase; EC 2.6.1.13), a pyridoxal-5'-phosphate-dependent mitochondrial enzyme controls the l-ornithine level in tissues by catalyzing the transfer of the delta-amino group of l-ornithine to 2-oxoglutarate, producing l-glutamate- gamma-semialdehyde and l-glutamate. (2S, 5S)-5-Fluoromethylornithine is the only inhibitor exclusively specific for ornithine aminotransferase known to date. Both in vitro and in vivo, it blocks the enzyme by a suicide reaction leading to a covalent adduct with the cofactor. The crystal structure of the enzyme-inhibitor complex was solved at a resolution of 1.95 A. No significant conformational changes compared with the native enzyme structure were observed. The structure reveals the atomic details of the cofactor-inhibitor adduct and its interactions with the active site of the enzyme. The main residues responsible for specific binding of the inhibitor are Arg180, which forms a strong salt bridge with the alpha-carboxylate and Tyr55, which is involved in a short hydrogen bond with the alpha-amino group. The experimental observation that in the racemic mixture, (2S, 5S)-5-fluoromethylornithine is exclusively responsible for the enzyme inhibition can be explained on the basis of the active site topology. Model building studies strongly suggest that the natural substrate l-ornithine, in its external aldimine adduct with the enzyme, makes use of the same recognition site as the inhibitor. It is proposed that the neutralization of the active site Arg413 by a salt bridge with Glu235 also plays an important role in productive binding of both 5-fluoromethylornithine and l-ornithine. Arg180 and Arg413 are believed to be instrumental in recognition of l-glutamate, by binding its gamma and alpha-carboxylate groups, respectively. This requires a different side-chain conformation of Glu235. Lys292 is the only obvious candidate for catalyzing the rate-limiting proton transfer steps in the transamination reaction.

PubMed: 9878407
DOI: 10.1006/jmbi.1998.2289

Experimental method

X-RAY DIFFRACTION (1.95 Å)