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 restrai nts between atoms in close spatial proximity, principally in the form of short (< 5 Angstrom) 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 i n the sequence may be insufficient to define their relative orientatio ns. In this paper we show how the dependence of heteronuclear longitud inal and transverse relaxation times on the rotational diffusion aniso tropy of non-spherical molecules can be readily used to directly provi de restraints for simulated annealing structure refinement that charac terize long range order a priori. The method is demonstrated using the N-terminal domain of Enzyme I, a protein of 259 residues comprising t wo distinct domains with a diffusion anisotropy (D-parallel to/D-perpe ndicular to of similar to 2.