The two-body (protein and probe) coupled rotator slowly relaxing local structure (SRLS) approach, implemented for NMR spin relaxation in proteins, is presented. SRLS is based on a Smoluchowki equation that includes the tensorial descriptions of the diffusing rotators and (via the local ordering) their dynamical coupling. This yields spectral densities that enter the expressions for the experimentally measured relaxation parameters. The constrained motion of the probe is treated by analogy with the standard treatments of restricted motions in liquids. Such restricted motions are largely recovered in the limit of large time scale separation between the rotators, i.e., when mode-coupling is not important. We found that the tensorial properties are not simple for proteins even in this limit. Their complexity has to be accounted for to obtain physically insightful pictures of protein dynamics. The traditional method for analyzing NMR spin relaxation in proteins is model-free (MF). This method treats only the simplest tensorial properties and implies large time-scale separation. Only when these conditions are fulfilled the analytical MF spectral densities, which are limiting cases of SRLS, may be used. Since they are not fulfilled in most actual cases, the MF-based pictures of protein dynamics are unreliable.
|State||Published - 2011|
Bibliographical noteFunding Information:
acknowledges support provided by the Italian Ministero dell’Istruzione, Universitàe Ricerca (MIUR Grant No. PRIN2006 2006033728), and by the University of Padova (Grant “Progetto Strategico” HELIOS 2009).
This work was supported by the Israel Science Foundation (Grant No. 347/07 to E. M.), the Binational Science Foundation (Grant No. 2 006 050 to E. M. and J. H. F.), the German-Israeli Science Foundation for Scientific Research and Development (Grant No. 928-190.0/2006 to E. M. and Christian Griesinger of Max Planck Institute, Göttingen, Germany), and the Damadian Center for Magnetic Resonance at Bar-Ilan University, Israel. This work was also supported by the National Center for Research Resources of the National Institutes of Health (Grant No. P41-RR016 292 to J. H. F.). A. P.
© 2011 John Wiley & Sons, Ltd.