title: Pseudo-merohedral twinning in monoclinic crystals of wild-type human brain neuroglobin.
abstract: The purification, crystallization and successful structure determination by molecular replacement of wild-type human brain neuroglobin at 1.8 A resolution is reported. The apparent space group was orthorhombic C222(1), but the real space group was monoclinic P2(1), which resulted from twinning. Indeed, the unit-cell parameters, a = 31.2, b = 139.1, c = 31.2 A, beta = 102 degrees , display a fortuitously close to c and twinning by the operator l, -k, h occurs. Twinning was not evident from the initial analysis of intensity distribution, but pseudo-merohedral twinning was revealed by the Padilla and Yeates test based on local intensity differences. A twinning fraction of 0.5 was determined in SHELXL, indicating a perfect hemihedrally twinned crystal. To date, this type of twinning has been reported in more than ten structures, which makes it quite a common case in proteins.
authors.affiliation: Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Gif-sur-Yvette, France.
authors.forename: Djemel
authors.initials: D
authors.lastname: Hamdane
authors.forename: Christophe
authors.initials: C
authors.lastname: Lechauve
authors.forename: Michael C
authors.initials: MC
authors.lastname: Marden
authors.forename: Béatrice
authors.initials: B
authors.lastname: Golinelli-Pimpaneau
mesh_terms: D001923:Brain Chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D003553:Cystine / Q000737:chemistry; D005914:Globins / Q000737:chemistry*; D006801:Humans; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000737:chemistry*; D000078787:Neuroglobin; D010100:Oxygen / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D003553:Cystine; D005914:Globins; D010100:Oxygen