Alignment of chain-like molecules.

The steric obstruction model, that describes the enhanced alignment of folded proteins by anisotropic medium, is extended to account for the residual dipolar couplings of chain-like polypeptides. The average alignment of each chain segment is calculated from an ensemble of conformations represented by a spatial probability distribution. The segmental alignment depends on chain length, flexibility and segment's position in the chain. Residual dipolar couplings in turn depend on internuclear vector directions within each fragment. The results of calculations and simulations explain salient features of the experimental data. With this insight residual dipolar couplings can be interpreted to assess the degree of denaturation, local structures and spatial organization of weakly structured proteins.