title: A pH-sensitive, colorful, lanthanide-chelating paramagnetic NMR probe.
abstract: Paramagnetic lanthanides ions are broadly used in NMR spectroscopy. The effects of unpaired electrons on NMR spectral parameters provide a powerful tool for the characterization of macromolecular structures and dynamics. Here, a new lanthanide-chelating NMR probe, Caged Lanthanide NMR Probe-7 (CLaNP-7), is presented. It can be attached to protein surfaces via two disulfide bridges, yielding a probe that is rigid relative to the protein backbone. CLaNP-7 extends the application range of available probes. It has a yellow color, which is helpful for sample preparation. Its effects are comparable to those of CLaNP-5, but its charge is two units lower (+1) than that of CLaNP-5 (+3), reducing the change in surface potential after probe attachment. It also has a different magnetic susceptibility tensor, so by using both tags, two sets of structural restraints can be obtained per engineered cysteine pair. Moreover, it was found that the orientation of the magnetic susceptibility tensor is pH dependent (pK(a) ≈ 7) when a histidine residue is located in the neighborhood of the probe attachment site. The results show that the His imidazole group interacts with the CLaNP-7 tag. It is proposed that the histidine residue forms a hydrogen bond to a water/hydroxyl molecule that occupies the ninth coordination position on the lanthanide, thus breaking the two-fold symmetry of the CLaNP tag in a pH-dependent way.
authors.affiliation: Gorlaeus Laboratories, Leiden Institute of Chemistry, Leiden University, 2300 RA Leiden, The Netherlands.
authors.forename: Wei-Min
authors.initials: WM
authors.lastname: Liu
authors.forename: Peter H J
authors.initials: PH
authors.lastname: Keizers
authors.forename: Mathias A S
authors.initials: MA
authors.lastname: Hass
authors.forename: Anneloes
authors.initials: A
authors.lastname: Blok
authors.forename: Monika
authors.initials: M
authors.lastname: Timmer
authors.forename: Alexi J C
authors.initials: AJ
authors.lastname: Sarris
authors.forename: Mark
authors.initials: M
authors.lastname: Overhand
authors.forename: Marcellus
authors.initials: M
authors.lastname: Ubbink
mesh_terms: D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D011506:Proteins / Q000737:chemistry
chemical_list: D002614:Chelating Agents; D005456:Fluorescent Dyes; D028581:Lanthanoid Series Elements; D011506:Proteins