title: Using Paramagnetism to Slow Down Nuclear Relaxation in Protein NMR.
abstract: Paramagnetic metal ions accelerate nuclear spin relaxation; this effect is widely used for distance measurement and called paramagnetic relaxation enhancement (PRE). Theoretical predictions established that, under special circumstances, it is also possible to achieve a reduction in nuclear relaxation rates (negative PRE). This situation would occur if the mechanism of nuclear relaxation in the diamagnetic state is counterbalanced by a paramagnetic relaxation mechanism caused by the metal ion. Here we report the first experimental evidence for such a cross-correlation effect. Using a uniformly15N-labeled mutant of calbindin D9kloaded with either Tm3+or Tb3+, reduced R1and R2relaxation rates of backbone15N spins were observed compared with the diamagnetic reference (the same protein loaded with Y3+). The effect arises from the compensation of the chemical shift anisotropy tensor by the anisotropic dipolar shielding generated by the unpaired electron spin.
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, ACT 2601, Australia.
authors.forename: Henry W
authors.initials: HW
authors.lastname: Orton
authors.affiliation: School of Chemistry, University of Southampton , Southampton, SO17 1BJ, United Kingdom.
authors.forename: Ilya
authors.initials: I
authors.lastname: Kuprov
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, ACT 2601, Australia.
authors.forename: Choy-Theng
authors.initials: CT
authors.lastname: Loh
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, ACT 2601, Australia.
authors.forename: Gottfried
authors.initials: G
authors.lastname: Otting
mesh_terms: D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011506:Proteins / Q000737:chemistry*
chemical_list: D011506:Proteins