Ligand-Capped Cobalt(II) Multiplies the Value of the Double-Histidine Motif for PCS NMR Studies

In structural studies by NMR, pseudocontact shifts (PCSs) provide both angular and distance information. For proteins, incorporation of a di-histidine (diHis) motif, coordinated to Co2+, has emerged as an important tool to measure PCS. Here, we show that using different Co(II)-chelating ligands, such as nitrilotriacetic acid (NTA) and iminodiacetic acid (IDA), resolves the isosurface ambiguity of Co2+-diHis and yields orthogonal PCS data sets with different Delta chi-tensors for the same diHis-bearing protein. Importantly, such capping ligands effectively eliminate undesired intermolecular interactions, which can be detrimental to PCS studies. Devising and employing ligand-capping strategies afford versatile and powerful means to obtain multiple orthogonal PCS data sets, significantly extending the use of the diHis motif for structural studies by NMR.

Automated summary

In NMR structural studies, pseudocontact shifts (PCSs) can provide both angular and distance information. The incorporation of a di-histidine (diHis) motif coordinated to Co2+ has become an important method for measuring PCS in proteins. This study demonstrates that using different Co(II)-chelating ligands resolves the ambiguity in the Co2+-diHis isosurfaces and produces orthogonal PCS data sets with different Delta chi-tensors for the same diHis-bearing protein. The use of capping ligands effectively eliminates undesired intermolecular interactions, enhancing the utility of the diHis motif for NMR structural studies.