Abstract
Some of the improvements in SHELX2013 make SHELXL convenient to use for refinement of macromolecular structures against neutron data without the support of X-ray data. The new NEUT instruction adjusts the behaviour of the SFAC instruction as well as the default bond lengths of the AFIX instructions. This work presents a protocol on how to use SHELXL for refinement of protein structures against neutron data. It includes restraints extending the Engh & Huber [Acta Cryst. (1991), A47, 392-400] restraints to H atoms and discusses several of the features of SHELXL that make the program particularly useful for the investigation of H atoms with neutron diffraction. SHELXL2013 is already adequate for the refinement of small molecules against neutron data, but there is still room for improvement, like the introduction of chain IDs for the refinement of macromolecular structures.
Highlights
Single-crystal neutron diffraction is an experimental technique complementary to X-ray diffraction
In this work we tested the improvements made to SHELXL2013 with respect to the refinement of macromolecular structures against neutron data
Our results include a set of restraints involving H atoms, listed in the supporting information, which extend the Engh & Huber (1991) restraints for amino acids
Summary
Single-crystal neutron diffraction is an experimental technique complementary to X-ray diffraction. Neutron diffraction does not change the oxidation state of ions, which is a common problem with synchrotron X-ray radiation (Hersleth & Andersson, 2011), magnetic properties can be investigated, and the strength of the interaction of neutrons with hydrogen and deuterium is of the same order of magnitude as with, for example, carbon, nitrogen or oxygen (Dianoux & Lander, 2003) For the latter reason, neutron diffraction is of particular interest for the examination of hydrogen-bond interactions between ligands and enzymes (Yamaguchi et al, 2009; Blakeley et al, 2008; Niimura & Bau, 2008).
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