title: Ambiguity assessment of small-angle scattering curves from monodisperse systems.
abstract: A novel approach is presented for an a priori assessment of the ambiguity associated with spherically averaged single-particle scattering. The approach is of broad interest to the structural biology community, allowing the rapid and model-independent assessment of the inherent non-uniqueness of three-dimensional shape reconstruction from scattering experiments on solutions of biological macromolecules. One-dimensional scattering curves recorded from monodisperse systems are nowadays routinely utilized to generate low-resolution particle shapes, but the potential ambiguity of such reconstructions remains a major issue. At present, the (non)uniqueness can only be assessed by a posteriori comparison and averaging of repetitive Monte Carlo-based shape-determination runs. The new a priori ambiguity measure is based on the number of distinct shape categories compatible with a given data set. For this purpose, a comprehensive library of over 14,000 shape topologies has been generated containing up to seven beads closely packed on a hexagonal grid. The computed scattering curves rescaled to keep only the shape topology rather than the overall size information provide a `scattering map' of this set of shapes. For a given scattering data set, one rapidly obtains the number of neighbours in the map and the associated shape topologies such that in addition to providing a quantitative ambiguity measure the algorithm may also serve as an alternative shape-analysis tool. The approach has been validated in model calculations on geometrical bodies and its usefulness is further demonstrated on a number of experimental X-ray scattering data sets from proteins in solution. A quantitative ambiguity score (a-score) is introduced to provide immediate and convenient guidance to the user on the uniqueness of the ab initio shape reconstruction from the given data set.
authors.affiliation: European Molecular Biology Laboratory, Hamburg Unit, EMBL c/o DESY, Notkestrasse 85, 22603 Hamburg, Germany.
authors.forename: Maxim V
authors.initials: MV
authors.lastname: Petoukhov
authors.affiliation: European Molecular Biology Laboratory, Hamburg Unit, EMBL c/o DESY, Notkestrasse 85, 22603 Hamburg, Germany.
authors.forename: Dmitri I
authors.initials: DI
authors.lastname: Svergun
mesh_terms: D000465:Algorithms; D000818:Animals; D002417:Cattle; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D009010:Monte Carlo Method; D009113:Muramidase / Q000737:chemistry*; D012194:RNA-Directed DNA Polymerase / Q000737:chemistry*; D053838:Scattering, Small Angle; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D012710:Serum Albumin, Bovine; D012194:RNA-Directed DNA Polymerase; D009113:Muramidase
keywords: AMBIMETER; ambiguity; shape determination; solution scattering; structural modelling; uniqueness