Ml. Raves et al., Joint refinement as a tool for thorough comparison between NMR and X-ray data and structures of HU protein, J BIOM NMR, 21(3), 2001, pp. 235-248
Joint refinement, i.e., the simultaneous refinement of a structure against
both nuclear magnetic resonance (NMR) spectroscopic and X-ray crystallograp
hic data, was performed on the HU protein from Bacillus stearothermophilus
(HUBst). The procedure was aimed at investigating the compatibility of the
two data sets and at identifying conflicting information. Wherever importan
t differences were found, such as peptide flips in the main-chain conformat
ion, the data were further analyzed to find the cause. The NMR data showed
some errors arising either from the manual interpretation of the spectra or
from the incorrect account for spin diffusion. The most important artefact
inherent to the X-ray data is the crystal packing of the molecules: the ef
fects range from the limitation of the freedom of the flexible parts of the
HUBst molecule to possibly one of the peptide flips.