Using Paramagnetism to Slow Down Nuclear Relaxation in Protein NMR

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• 作者：Henry W. Orton ; Ilya Kuprov ; Choy-Theng Loh ; Gottfried Otting
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：December 1, 2016
• 年：2016
• 卷：7
• 期：23
• 页码：4815-4818
• 全文大小：312K
• ISSN：1948-7185

文摘

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 uniformly ¹⁵N-labeled mutant of calbindin D_9k loaded with either Tm³⁺ or Tb³⁺, reduced R₁ and R₂ relaxation rates of backbone ¹⁵N 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.