title: Efficient merging of data from multiple samples for determination of anomalous substructure.
abstract: Merging of data from multiple crystals has proven to be useful for determination of the anomalously scattering atomic substructure for crystals with weak anomalous scatterers (e.g. S and P) and/or poor diffraction. Strategies for merging data from many samples, which require assessment of sample isomorphism, rely on metrics of variability in unit-cell parameters, anomalous signal correlation and overall data similarity. Local scaling, anomalous signal optimization and data-set weighting, implemented in phenix.scale_and_merge, provide an efficient protocol for merging data from many samples. The protein NS1 was used in a series of trials with data collected from 28 samples for phasing by single-wavelength anomalous diffraction of the native S atoms. The local-scaling, anomalous-optimization protocol produced merged data sets with higher anomalous signal quality indicators than did standard global-scaling protocols. The local-scaled data were also more successful in substructure determination. Merged data quality was assessed for data sets where the multiplicity was reduced in either of two ways: by excluding data from individual crystals (to reduce errors owing to non-isomorphism) or by excluding the last-recorded segments of data from each crystal (to minimize the effects of radiation damage). The anomalous signal was equivalent at equivalent multiplicity for the two procedures, and structure-determination success correlated with anomalous signal metrics. The quality of the anomalous signal was strongly correlated with data multiplicity over a range of 12-fold to 150-fold multiplicity. For the NS1 data, the local-scaling and anomalous-optimization protocol handled sample non-isomorphism and radiation-induced decay equally well.
authors.affiliation: Life Sciences Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, MI 48109-2216, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Akey
authors.affiliation: Bioscience Division, Los Alamos National Laboratory, Mail Stop M888, Los Alamos, NM 87545, USA.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Terwilliger
authors.affiliation: Life Sciences Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, MI 48109-2216, USA.
authors.forename: Janet L
authors.initials: JL
authors.lastname: Smith
mesh_terms: D018360:Crystallography, X-Ray / Q000379:methods*; D005416:Flavivirus / Q000737:chemistry*; D011487:Protein Conformation; D013455:Sulfur / Q000737:chemistry*; D017361:Viral Nonstructural Proteins / Q000737:chemistry*
chemical_list: C100315:NS1 protein, Flavivirus; D017361:Viral Nonstructural Proteins; D013455:Sulfur
keywords: anomalous scattering; data merging; local scaling; sulfur phasing