Lineshape Analysis as a Tool for Probing Functional Motions at Biological Interfaces

Abstract

The analysis of peak lineshapes in two-dimensional NMR spectra acquired during titration experiments is a powerful technique for quantitative studies of biological interfaces. The theoretical basis for how the thermodynamics (equilibrium populations) and kinetics (rate constants) of a multi-state equilibrium are encoded in the lineshape of an NMR peak is presented. Insights on how an exchange process influences the observed magnetization, how to construct the rate matrix for a given reaction scheme, and the origins of the governing lineshape equation are included. Applications of lineshape analysis to two-state binding and to four-state peptidyl prolyl cis–trans isomerization reactions involved in Alzheimer's disease and lateral root development in rice are presented. These studies illustrate how lineshape analysis of NMR titration experiments provides key mechanistic details for understanding the role of biological interfaces. Importantly, the quantitative model obtained from observations of an exchange reaction in the NMR tube enables predictions of activity to be scaled to cellular concentrations. This method is highly complementary to more recently developed NMR relaxation techniques. The application of lineshape analysis and relaxation methods to the same samples could enable quantitative characterization of even more complex multi-state systems.