title: Single-wavelength phasing strategy for quasi-racemic protein crystal diffraction data.
abstract: Racemic protein crystallography offers two key features: an increased probability of crystallization and the potential advantage of phasing centric diffraction data. In this study, a phasing strategy is developed for the scenario in which a crystal is grown from a mixture in which anomalous scattering atoms have been incorporated into only one enantiomeric form of the protein molecule in an otherwise racemic mixture. The structure of a protein crystallized in such a quasi-racemic form has been determined in previous work [Pentelute et al. (2008), J. Am. Chem. Soc. 130, 9695-9701] using the multiwavelength anomalous dispersion (MAD) method. Here, it is shown that although the phases from such a crystal are not strictly centric, their approximate centricity provides a powerful way to break the phase ambiguity that ordinarily arises when using the single-wavelength anomalous dispersion (SAD) method. It is shown that good phases and electron-density maps can be obtained from a quasi-racemic protein crystal based on single-wavelength data. A prerequisite problem of how to establish the origin of the anomalous scattering substructure relative to the center of pseudo-inversion is also addressed.
authors.affiliation: UCLA-DOE Institute for Genomics and Proteomics, University of California, Los Angeles, CA 90095, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Sawaya
authors.forename: Brad L
authors.initials: BL
authors.lastname: Pentelute
authors.forename: Stephen B H
authors.initials: SB
authors.lastname: Kent
authors.forename: Todd O
authors.initials: TO
authors.lastname: Yeates
mesh_terms: D000818:Animals; D021301:Antifreeze Proteins / Q000032:analysis* / Q000737:chemistry; D018360:Crystallography, X-Ray / Q000379:methods*; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D005423:Siphonaptera / Q000737:chemistry
chemical_list: D021301:Antifreeze Proteins