title: Multiple isomorphous replacement on merohedral twins: structure determination of deacetoxycephalosporin C synthase.
abstract: Merohedral twinning is a packing anomaly that seriously impairs the determination of macromolecular crystal structures. Crystals of deacetoxycephalosporin C synthase (DAOCS), an enzyme involved in the expansion of the penicillin nucleus to form the core structure of the cephalosporin antibiotics, were found to be merohedrally twinned by many diagnostic criteria. Here, the structure determination of DAOCS from twinned crystals based on a combination of isomorphous replacement and the use of a multiple-wavelength diffraction data set is described.
authors.affiliation: Department of Molecular Biology, Swedish University of Agricultural Sciences, Box 590, S-751 24 Uppsala, Sweden. anke@xray.bmc.uu.se
authors.forename: A C
authors.initials: AC
authors.lastname: Terwisscha van Scheltinga
authors.forename: K
authors.initials: K
authors.lastname: Valegård
authors.forename: S
authors.initials: S
authors.lastname: Ramaswamy
authors.forename: J
authors.initials: J
authors.lastname: Hajdu
authors.forename: I
authors.initials: I
authors.lastname: Andersson
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D019751:Intramolecular Transferases / Q000737:chemistry*; D008958:Models, Molecular; D046915:Penicillin-Binding Proteins; D011487:Protein Conformation
chemical_list: D046915:Penicillin-Binding Proteins; D019751:Intramolecular Transferases; C038371:deacetoxycephalosporin C synthetase