Three-Dimensional Protein Structure Determination Using Pseudocontact Shifts of Backbone Amide Protons Generated by Double-Histidine Co2+-Binding Motifs at Multiple Sites.

Pseudocontact shifts (PCSs) generated by paramagnetic metal ions contribute highly informative long-range structure restraints that can be measured in solution and are ideally suited to guide structure prediction algorithms in determining global protein folds. We recently demonstrated that PCSs, which are relatively small but of high quality, can be generated by a double-histidine (dHis) motif in an α-helix, which provides a well-defined binding site for a single Co2+ ion. Here we show that PCSs of backbone amide protons generated by dHis-Co2+ motifs positioned in four different α-helices of a protein deliver excellent restraints to determine the three-dimensional (3D) structure of a protein in a way akin to the global positioning system (GPS). We demonstrate the approach with GPS-Rosetta calculations of the 3D structure of the C-terminal domain of the chaperone ERp29 (ERp29-C). Despite the relatively small size of the PCSs generated by the dHis-Co2+ motifs, the structure calculations converged readily. Generating PCSs by the dHis-Co2+ motif thus presents an excellent alternative to the use of lanthanide tags.