better integrate protein structure features (including solvent accessible surface area) and local or nearest-neighbor interactions. This led to the release of an updated version of ShiftX called ShiftX2. ShiftX2 is substantially more accurate than ShiftX and it is able to calculate a much larger collection of side chain chemical shifts (1H, 13C and 15N). It is also available as a freely accessible web server. However, it is 2-3X slower. ShiftX2 achieves correlation coefficients between experimentally observed and predicted backbone chemical shifts of 0.98 (15N), 0.99 (13CA), 0.999 (13CB), 0.97 (13CO), 0.97 (1HN), 0.98 (1HA) with corresponding RMS errors of 1.12, 0.44, 0.51, 0.53, 0.17, and 0.12 ppm. See also Protein Protein NMR NMR Chemical shift Random Coil Index Protein Chemical Shift Re-Referencing Protein secondary structure Protein Chemical Shift Prediction Protein structure prediction Crystallography Protein data bank References Biological databases