title: Acetobacter turbidans alpha-amino acid ester hydrolase: merohedral twinning in P21 obscured by pseudo-translational NCS.
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.
authors.affiliation: University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: Thomas R M
authors.initials: TR
authors.lastname: Barends
authors.forename: Bauke W
authors.initials: BW
authors.lastname: Dijkstra
mesh_terms: D000091:Acetobacter / Q000201:enzymology*; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D011994:Recombinant Proteins; D002265:Carboxylic Ester Hydrolases; C058058:alpha-amino acid esterase