title: Processing incommensurately modulated protein diffraction data with Eval15.
abstract: Recent challenges in biological X-ray crystallography include the processing of modulated diffraction data. A modulated crystal has lost its three-dimensional translational symmetry but retains long-range order that can be restored by refining a periodic modulation function. The presence of a crystal modulation is indicated by an X-ray diffraction pattern with periodic main reflections flanked by off-lattice satellite reflections. While the periodic main reflections can easily be indexed using three reciprocal-lattice vectors a*, b*, c*, the satellite reflections have a non-integral relationship to the main lattice and require a q vector for indexing. While methods for the processing of diffraction intensities from modulated small-molecule crystals are well developed, they have not been applied in protein crystallography. A recipe is presented here for processing incommensurately modulated data from a macromolecular crystal using the Eval program suite. The diffraction data are from an incommensurately modulated crystal of profilin-actin with single-order satellites parallel to b*. The steps taken in this report can be used as a guide for protein crystallographers when encountering crystal modulations. To our knowledge, this is the first report of the processing of data from an incommensurately modulated macromolecular crystal.
authors.affiliation: The Eppley Institute for Research in Cancer and Allied Diseases, Nebraska Medical Center, Omaha, NE 68198-7696, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Porta
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Lovelace
authors.forename: Antoine M M
authors.initials: AM
authors.lastname: Schreurs
authors.forename: Loes M J
authors.initials: LM
authors.lastname: Kroon-Batenburg
authors.forename: Gloria E O
authors.initials: GE
authors.lastname: Borgstahl
mesh_terms: D000199:Actins / Q000032:analysis* / Q000378:metabolism; D000818:Animals; D002417:Cattle; D018360:Crystallography, X-Ray / Q000379:methods*; D051304:Profilins / Q000032:analysis* / Q000378:metabolism; D011485:Protein Binding; D012985:Software Design
chemical_list: D000199:Actins; D051304:Profilins