Man, BradleySu, Xun-ChengLiang, HaoboSimonsen, ShaneMesserle, Barbara AnnOtting, GottfriedHuber, Thomas2015-12-070947-6539http://hdl.handle.net/1885/26014Paramagnetic effects from lanthanide ions present powerful tools for protein studies by nuclear magnetic resonance (NMR) spectroscopy provid-ed that the lanthanide can be site-spe-cifically and rigidly attached to the pro-tein. A new, particularly small and rigid lanthanide-binding tag, 3-mercap-to-2, 6-pyridinedicarboxylic acid (3MDPA), was synthesized and at-tached to two different proteins via a disulfide bond. The complexes of the N-terminal domain of the E. coli argi-nine repressor (ArgN) with seven dif-ferent paramagnetic lanthanide ions and Co2+ were analyzed in detail by NMR spectroscopy. The magnetic sus-ceptibility anisotropy (ΔX) tensors and metal position were determined from pseudocontact shifts. The 3MDPA tag generated very different Ax tensor ori-entations compared to the previously studied 4-mercaptomethyl-DPA tag, making it a highly complementary and useful tool for protein NMR studies.Keywords: Disulfide bonds; E. coli; Lanthanide ion; Lanthanides; N-terminal domains; NMR spectroscopy; NMR studies; Paramagnetic effect; Protein labeling; Pyridinedicarboxylic acids; Acids; Cobalt compounds; Dyes; Escherichia coli; Labeling; Magnetic properties; Nu Lanthanides; Magnetic properties; NMR spec-troscopy; Protein labeling; Pseudocontact shifts201010.1002/chem.2009029042016-02-24