MIR phasing using merohedrally twinned crystals.
Merohedral twinning is a crystal-growth disorder that seriously hinders the determination of macromolecular crystal structures by isomorphous replacement. The strategies used in the structures solved so far are discussed. Several methods can be used to determine the extent of twinning, the twin fraction and to detwin the data. Accurate determination of the twin fraction by analysing heavy-atom refinement statistics is possible, but only influences the resulting phases slightly. It seems more crucial to restrict the variation in twin fractions between data sets, either by making the twin fractions of some data sets artificially higher or by screening crystals to obtain data with a low twin fraction.
Terwisscha van Scheltinga
Anke C
AC
Department of Molecular Biology, Swedish University of Agricultural Sciences, Box 590, S-751 24 Uppsala, Sweden. anke@xray.bmc.uu.se
Valegård
Karin
K
Hajdu
Janos
J
Andersson
Inger
I
D043422:Carboxypeptidases A / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods*; D019751:Intramolecular Transferases / Q000737:chemistry; D010088:Oxidoreductases / Q000737:chemistry; D046915:Penicillin-Binding Proteins; D010544:Peroxidases / Q000737:chemistry; D054464:Peroxiredoxins; D010799:Phycoerythrin / Q000737:chemistry
D046915:Penicillin-Binding Proteins; D010799:Phycoerythrin; D010088:Oxidoreductases; D010544:Peroxidases; D054464:Peroxiredoxins; C021401:hydroxylamine dehydrogenase; D043422:Carboxypeptidases A; D019751:Intramolecular Transferases; C038371:deacetoxycephalosporin C synthetase