New developments in the ATSAS program package for small-angle scattering data analysis

Abstract

New developments in the program package ATSAS (version 2.4) for the processing and analysis of isotropic small-angle X-ray and neutron scattering data are described. They include (i) multiplatform data manipulation and display tools, (ii) programs for automated data processing and calculation of overall parameters, (iii) improved usage of high- and low-resolution models from other structural methods, (iv) new algorithms to build three-dimensional models from weakly interacting oligomeric systems and complexes, and (v) enhanced tools to analyse data from mixtures and flexible systems. The new ATSAS release includes installers for current major platforms (Windows, Linux and Mac OSX) and provides improved indexed user documentation. The web-related developments, including a user discussion forum and a widened online access to run ATSAS programs, are also presented.

Keywords: ATSAS; biological macromolecules; computer programs; data analysis; isotropic scattering; small-angle scattering; structural modelling.

Figure 1

Major analysis tasks and computational modules of the ATSAS program package. Newly developed programs and the ones significantly enhanced in the 2.4 release are given in black capital letters.

Figure 2

Screenshots of the cross-platform PRIMUS. (a) One experimental profile with errors is displayed. The ‘Documents’ panel may be undocked and moved freely. It may hold a (virtually) unlimited number of files, provides access to the most frequently used operations and keeps a list of recently used files. (b) Interactive estimation of the radius of gyration. Advanced options are hidden by default; the display of residuals may be enabled or disabled. Zooming, panning and export to various graphics formats are available. (c) Estimation of the distance distribution; the fit to the data and the P(r) function are shown next to each other and instantly updated if any of the configuration options is changed. Advanced options are hidden by default.

Figure 3

Schematic representation of some new algorithms introduced in ATSAS 2.4. (a) Clustering of multiple models by DAMCLUST. The program suggests the optimal way of splitting multiple models into groups based on the distance criteria (either NSD or r.m.s.d.). In the presented example, seven models are split into three groups (indicated by the dashed line), whereby there are three models in the first group while the second and the third groups contain two models each. (b) Modelling algorithms for transient complexes (SASREFMX) and unstable oligomers (GASBORMX/SASREFMX) provide means of three-dimensional structure analysis of equilibrium mixtures, if no monodisperse samples can be obtained. (c) Rigid-body modelling of complexes with addition of missing loops by CORAL, which combines the capabilities of SASREF and BUNCH. The modelling of complicated cases with incomplete structures of the subunits is possible, whereby the RANLOGS library is used for selection of templates for missing linkers. (d) A new implementation of RANCH from the EOM package enables generation of random pools containing multimeric structures having fixed symmetric cores with or without imposed symmetry for the rest of the molecule.

Figure 4

Screenshot of SASDOC showing the list of ATSAS manuals available. The highlighted entry in the contents pane (left) is shown in a tab in the main part of the window. A built-in full text search, an index and bookmarks are available.