Inference of macromolecular assemblies from crystalline state.

A program suite for one-dimensional small-angle scattering data processing running on IBM-compatible PCs under Windows 9x/NT/2000/XP is presented. The main program, PRIMUS, has a menu-driven graphical user interface calling computational modules to perform data manipulation and analysis. Experimental data in binary OTOKO format can be reduced by calling the program SAPOKO, which includes statistical analysis of time frames, averaging and scaling. Tools to generate the angular axis and detector response files from diffraction patterns of calibration samples, as well as binary to ASCII transformation programs, are available. Several types of ASCII files can be directly imported into PRIMUS, in particular, sasCIF or ILL-type files are read without modification. PRIMUS provides basic data manipulation functions (averaging, background subtraction, merging of data measured in different angular ranges, extrapolation to zero sample concentration, etc.) and computes invariants from Guinier and Porod plots. Several external modules coupled with PRIMUS via pop-up menus enable the user to evaluate the characteristic functions by indirect Fourier transformation, to perform peak analysis for partially ordered systems and to find shape approximations in terms of three-parametric geometrical bodies. For the analysis of mixtures, PRIMUS enables model-independent singular value decomposition or linear fitting if the scattering from the components is known. An interface is also provided to the general non-linear fitting program MIXTURE, which is designed for quantitative analysis of multicomponent systems represented by simple geometrical bodies, taking shape and size polydispersity as well as interparticle interference effects into account.

PRIMUS: a Windows PC-based system for small-angle scattering data analysis

https://www.embl-hamburg.de/biosaxs/reprints/dammin_1999.pdf

Restoring low resolution structure of biological macromolecules from solution scattering using simulated annealing.

Scattering patterns from geometrical bodies with different shapes and anisometry (solid and hollow spheres, cylinders, prisms) are computed and the shapes are reconstructed ab initio using envelope function and bead modelling methods. A procedure is described to analyze multiple solutions provided by bead modeling methods and to estimate stability and reliability of the shape reconstruction. It is demonstrated that flat shapes are more difficult to restore than elongated ones and types of shapes are indicated, which require additional information for reliable shape reconsrtuction from the scattering data.

/pdf/uniqueness-of-ab-initio-shape-determination-in-small-angle-1r29nkzxmv.pdf

Uniqueness of ab initio shape determination in small-angle scattering

DAMMIF, a revised implementation of the ab-initio shape-determination program DAMMIN for small-angle scattering data, is presented. The program was fully rewritten, and its algorithm was optimized for speed of execution and modified to avoid limitations due to the finite search volume. Symmetry and anisometry constraints can be imposed on the particle shape, similar to DAMMIN. In equivalent conditions, DAMMIF is 25–40 times faster than DAMMIN on a single CPU. The possibility to utilize multiple CPUs is added to DAMMIF. The application is available in binary form for major platforms.

/pdf/dammif-a-program-for-rapid-ab-initio-shape-determination-in-10nsawhr7n.pdf

DAMMIF, a program for rapid ab-initio shape determination in small-angle scattering

Small-angle scattering of X rays and neutrons is a widely used diffraction method for studying the structure of matter. This method of elastic scattering is used in various branches of science and technology, includ ing condensed matter physics, molecular biology and biophysics, polymer science, and metallurgy. Many small-angle scattering studies are of value for pure science and practical applications. It is well known that the most general and informative method for investigating the spatial structure of matter is based on wave-diffraction phenomena. In diffraction experiments a primary beam of radiation influences a studied object, and the scattering pattern is analyzed. In principle, this analysis allows one to obtain information on the structure of a substance with a spatial resolution determined by the wavelength of the radiation. Diffraction methods are used for studying matter on all scales, from elementary particles to macro-objects. The use of X rays, neutrons, and electron beams, with wavelengths of about 1 A, permits the study of the condensed state of matter, solids and liquids, down to atomic resolution. Determination of the atomic structure of crystals, i.e., the arrangement of atoms in a unit cell, is an important example of this line of investigation."

Structure Analysis by Small-Angle X-Ray and Neutron Scattering

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Structure Analysis by Small-Angle X-Ray and Neutron Scattering