Structure Report for: 1NX9

Barends, T.R.M., Polderman-Tijmes, J.J., Jekel, P.A., Janssen, D.B., Dijkstra, B.W

Title: Acetobacter turbidans alpha-amino acid ester hydrolase: how a single mutation improves an antibiotic-producing enzyme
Barends TR, Polderman-Tijmes JJ, Jekel PA, Williams C, Wybenga G, Janssen DB, Dijkstra BW
Ref: Journal of Biological Chemistry, 281:5804, 2006 : PubMed
Abstract


ESTHER: Barends_2006_J.Biol.Chem_281_5804
PubMedSearch: Barends 2006 J.Biol.Chem 281 5804
PubMedID: 16377627
Gene_locus related to this paper: acepa-AEHA

Abstract

The alpha-amino acid ester hydrolase (AEH) from Acetobacter turbidans is a bacterial enzyme catalyzing the hydrolysis and synthesis of beta-lactam antibiotics. The crystal structures of the native enzyme, both unliganded and in complex with the hydrolysis product D-phenylglycine are reported, as well as the structures of an inactive mutant (S205A) complexed with the substrate ampicillin, and an active site mutant (Y206A) with an increased tendency to catalyze antibiotic production rather than hydrolysis. The structure of the native enzyme shows an acyl binding pocket, in which D-phenylglycine binds, and an additional space that is large enough to accommodate the beta-lactam moiety of an antibiotic. In the S205A mutant, ampicillin binds in this pocket in a non-productive manner, making extensive contacts with the side chain of Tyr(112), which also participates in oxyanion hole formation. In the Y206A mutant, the Tyr(112) side chain has moved with its hydroxyl group toward the catalytic serine. Because this changes the properties of the beta-lactam binding site, this could explain the increased beta-lactam transferase activity of this mutant.



        

Title: Acetobacter turbidans alpha-amino acid ester hydrolase: merohedral twinning in P21 obscured by pseudo-translational NCS
Barends TR, Dijkstra BW
Ref: Acta Crystallographica D Biol Crystallogr, 59:2237, 2003 : PubMed
Abstract


ESTHER: Barends_2003_Acta.Crystallogr.D.Biol.Crystallogr_59_2237
PubMedSearch: Barends 2003 Acta.Crystallogr.D.Biol.Crystallogr 59 2237
PubMedID: 14646082
Gene_locus related to this paper: acepa-AEHA

Abstract

The structure elucidation of the alpha-amino acid ester hydrolase from Acetobacter turbidans by molecular replacement is described. In the monoclinic crystal, the molecules are related by both rotational and pseudo-crystallographic translational NCS (non-crystallographic symmetry). Refinement of the structure converged at unacceptably high R factors. After re-evaluation of the data, it was found that the crystal was merohedrally twinned, with a high twinning fraction. It is shown that the pseudo-crystallographic NCS causes aberrant behaviour of conventional twinning indicators, which explains why the twinning was only realized at the refinement stage.