Incorporation of residual chemical shift anisotropy into the treatment of 15N pseudocontact shifts for structural refinement

Paramagnetic NMR experiments, including the pseudocontact shift experiment, have seen increasing use due to recently developed probes and labeling strategies. The pseudocontact shift experiment can provide valuable intra- or inter-molecular distance and orientation information. However, the use of 1H/13C or 1H/15N PCS data in structure calculations is currently complicated by the contribution of residual chemical shift anisotropy to the 13C or 15N datasets. Here, we present a corrected PCS energy term for the software package Xplor-NIH with the appropriate residual chemical shift anisotropy correction and show its suitability for model refinements of ubiquitin labeled at residue 57 with a Tm-M8-SPy tag. For data taken at 800 MHz, the improvement with the corrected energy term is sufficient to make the quality of the fit for the 15N dataset comparable to that of the 1H dataset, for which no correction is needed. The corrected energy term is expected to become more relevant with increased use of higher field instruments and as new paramagnetic probes with larger magnetic susceptibility tensors continue to be developed.

Automated summary

Paramagnetic NMR experiments, including the pseudocontact shift experiment, have become increasingly popular due to the development of new probes and labeling strategies. The pseudocontact shift experiment can provide valuable information about distances and orientations within or between molecules. However, the use of 1H/13C or 1H/15N PCS data in structure calculations is currently complicated by the contribution of residual chemical shift anisotropy. In this study, a corrected PCS energy term for the Xplor-NIH software package is presented, along with its suitability for refining the structure of ubiquitin labeled at residue 57 with a Tm-M8-SPy tag. The corrected energy term improves the quality of the fit for the 15N dataset, making it comparable to the 1H dataset.