Local mobility of 15N labeled biomolecules characterized through cross-correlation rates: Applications to paramagnetic proteins* |
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Authors: | Isabella C Felli Hervé Desvaux Geoffrey Bodenhausen |
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Institution: | (1) Department of Chemistry, University of Florence, Via Gino Capponi 7, I-50121 Florence, Italy;(2) Service de Chimie Moléculaire, Commissariat à l'Energie Atomique, Saclay, F-91191 Gif-sur-Yvette, France;(3) Département de Chimie, Ecole Normale Supérieure, 24 rue Lhomond, F-75231 Paris cedex 05, France |
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Abstract: | The mobility of 15N labeled proteins can be characterized by measuring the cross-correlation rates N,NI that govern the conversion of Zeeman order Nz of an amide 15N nucleus into longitudinal two-spin order 2NzIz involving the amide 15N and 1H nuclei. This represents an alternative to the measurement of 15N self-relaxation rates 1/T1 and 1/T2 or 1/T1 . The rate of interconversion between Nz and 2NzIz is due to cross-correlation between fluctuations of different interactions and is not affected by a variety of relaxation mechanisms that contribute to the self-relaxation rates 1/T1, 1/T2 and 1/T1 . Spin diffusion among protons, which affects the measurements, can be quenched by various means that are evaluated by experiments and simulations. By applying an off-resonance radio-frequency (RF) field in the vicinity of the nitrogen resonance, the spectral density function J( ) can be determined at the frequency origin and at the nitrogen Larmor frequency. The methods are applied to the paramagnetic High-Potential Iron-Sulfur Protein iso I (HiPIP I) from E. halophila in its reduced state. |
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Keywords: | cross-correlation protein dynamics spin diffusion |
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