A new software suite, called Crystallography & NMR System (CNS), has been developed for macromolecular structure determination by X-ray crystallography or solution nuclear magnetic resonance (NMR) spectroscopy. In contrast to existing structure-determination programs the architecture of CNS is highly flexible, allowing for extension to other structure-determination methods, such as electron microscopy and solid-state NMR spectroscopy. CNS has a hierarchical structure: a high-level hypertext markup language (HTML) user interface, task-oriented user input files, module files, a symbolic structure-determination language (CNS language), and low-level source code. Each layer is accessible to the user. The novice user may just use the HTML interface, while the more advanced user may use any of the other layers. The source code will be distributed, thus source-code modification is possible. The CNS language is sufficiently powerful and flexible that many new algorithms can be easily implemented in the CNS language without changes to the source code. The CNS language allows the user to perform operations on data structures, such as structure factors, electron-density maps, and atomic properties. The power of the CNS language has been demonstrated by the implementation of a comprehensive set of crystallographic procedures for phasing, density modification and refinement. User-friendly task-oriented input files are available for nearly all aspects of macromolecular structure determination by X-ray crystallography and solution NMR.

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Crystallography & NMR System: A New Software Suite for Macromolecular Structure Determination

J. Appl. Cryst.の発刊に際して

Crystal structure of the eukaryotic DNA polymerase processivity factor PCNA

The sequence, crystal structure determination and refinement of two crystal forms of lipase B from Candida antarctica.

Reaction mechanism of alkaline phosphatase based on crystal structures. Two-metal ion catalysis.

An improved protocol for crystallographic refinement by simulated annealing is presented. It consists of slow cooling starting at high temperatures. Tests of refinements of aspartate aminotransferase and procin pepsin show that the slow-cooling protocol produces lower R factors and better geometry than other protocols previously published. The influence of the temperature-control method, weighting, cooling rate and duration of the heating stage on the success of the slow-cooling protocol is studied. Analysis of the time course of the potential-energy fluctuations indicates no global changes in the state of order of the system. Fluctuations of the potential energy are interpreted as localized conformational changes during the course of the refinement.

A. Krukowski

Papers

Slow-cooling protocols for crystallographic refinement by simulated annealing