MatchMaps: non-isomorphous difference maps for X-ray crystallography.

Area of Science:

• * Structural biology
• * Crystallography
• * Computational biology

Background:

• * Macromolecular functions are mediated by conformational changes.
• * Crystallography is a powerful tool for mapping these structural dynamics.
• * Isomorphous difference maps are sensitive but limited by crystal unit-cell variations.

Purpose of the Study:

• * To develop a generalized procedure for calculating observed difference maps.
• * To create a robust method for detecting conformational changes insensitive to unit-cell variations.
• * To implement this procedure in an accessible, open-source software package.

Main Methods:

• * Development of a generalized procedure for calculating observed difference maps.
• * Implementation of the procedure in the open-source Python package, MatchMaps.
• * Compatibility with established crystallographic software environments like PHENIX and CCP4.

Main Results:

• * MatchMaps successfully 'rescues' difference electron-density maps from poorly isomorphous crystals.
• * The software corrects artifacts in nominally isomorphous difference maps.
• * It detects conformational differences within asymmetric units and across different crystal forms.

Conclusions:

• * A novel, robust method for analyzing crystallographic data to reveal conformational changes has been established.
• * MatchMaps enhances the sensitivity and applicability of difference electron-density map analysis.
• * This tool provides broader utility for structural biologists studying dynamic macromolecules.