Computational Tools for Macromolecular Neutron Crystallography (MNC) is a consortium between Los Alamos National Laboratory(LANL) and Lawrence Berkeley National Laboratory (LBL). Our aim has been to address the need for new computational tools and methods to deal with the increasing number of neutron macromolecular structures being determined and their increasing size and complexity.
To that end, a patch, designated nCNS, for the existing structure solution program called CNSsolve was developed which combines, for the first time, global X-ray, neutron and energy refinement with cross-validated maximum likelihood simulated annealing refinement. nCNS can be used for X-ray, neutron or joint X-ray and neutron analyses and will be available as part of the standard CNS distribution.
Building on this success we are now continuing our development of new computational tools within the PHENIX suite. Neutron capabilities have been added to PHENIX, an NIH-funded collaborative project between several groups. The phenix.refine program offers a broad variety of efficient and fully automated tools for structure refinement using X-ray and neutron crystallography or both, such as restrained refinement at low resolution, simulated annealing and TLS modelling using maximum-likelihood targets, automatic detection and use of NCS, automatic detection and use of twinning information, sophisticated bulk-solvent correction and anisotropic scaling protocols, efficient handling of H atoms and refinement at ultra-high resolution. It is now possible to perform neutron and joint X-ray/neutron refinement in phenix.refine and deposit the resulting files in the Protein Data Bank.