Anisotropic Collective Motion Contributes to Nuclear Spin Relaxation in Crystalline Proteins

A model for calculating the influence of anisotropic collective motions on NMR relaxation rates in crystalline proteins is presented. We show that small-amplitude (<10 degrees) fluctuations may lead to substantial contributions to the N-15 spin-lattice relaxation rates and propose that the effect of domain motions should be included in solid-state NMR analyses of protein dynamics.