A method for incorporating dipolar couplings into structure calculations in cases of (near) axial symmetry of alignment

A method for incorporating dipolar coupling restraints into structure calculations is described which follows closely on methodology that has been recently presented for orienting peptide planes using dipolar couplings [Mueller et al. (2000) J. Mol. Biol., 300, 197-212] and is specifically developed for use in cases of an axially symmetric alignment tensor. Modeling studies on an all alpha -helical protein, farnesyl diphosphate synthase, establish the utility of the approach. A global fold of the 370-residue maltose binding protein in complex with beta -cyclodextrin is obtained from experimentally derived restraints. The average pairwise rmsd values between the N- and C-terminal domains in this NMR structure and the corresponding regions in the X-ray structure of the protein are 2.8 and 3.1 Angstrom, respectively.