Defining long range order in NMR structure determination from the dependence of heteronuclear relaxation times on rotational diffusion anisotropy.

Structure determination by NMR presently relies on short range restraints between atoms in close spatial proximity, principally in the form of short (< 5 A) interproton distances. In the case of modular or multidomain proteins and linear nucleic acids, the density of short interproton distance contacts between structural elements far apart in the sequence may be insufficient to define their relative orientations. In this paper we show how the dependence of heteronuclear longitudinal and transverse relaxation times on the rotational diffusion anisotropy of non-spherical molecules can be readily used to directly provide restraints for simulated annealing structure refinement that characterize long range order a priori. The method is demonstrated using the N-terminal domain of Enzyme I,a protein of 259 residues comprising two distinct domains with a diffusion anisotropy(Dparallel/Dperpendicular)of approximately 2.