Theoretical analysis of residual dipolar coupling patterns in regular secondary structures of proteins

A new approach to the interpretation of residual dipolar couplings for the regular secondary structures of proteins is presented. This paper deals with the analysis of the steric and chiral requirements of protein secondary structures and establishes a quantitative correlation between structure periodicity and the experimental values of the backbone residual dipolar couplings. Building on the recent interpretation of the periodicity of residual dipolar couplings in α-helices (i.e., "dipolar waves"), a general parametric equation for fitting the residual dipolar couplings of any regular secondary structure is derived. This equation interprets the modulation of the residual dipolar couplings' periodicity in terms of the secondary structure orientation with respect to an arbitrary reference frame, laying the groundwork for using backbone residual dipolar couplings as a fast tool for determining protein folding by NMR spectroscopy.