Direct detection of CH/π interactions in proteins

Abstract

XH/π interactions make important contributions to biomolecular structure and function. These weakly polar interactions, involving π-system acceptor groups, are usually identified from the three-dimensional structures of proteins. Here, nuclear magnetic resonance spectroscopy has been used to directly detect methyl/π (Me/π) interactions in proteins at atomic resolution. Density functional theory calculations predict the existence of weak scalar (J) couplings between nuclei involved in Me/π interactions. Using an optimized isotope-labelling strategy, these J couplings have been detected in proteins using nuclear magnetic resonance spectroscopy. The resulting spectra provide direct experimental evidence of Me/π interactions in proteins and allow a simple and unambiguous assignment of donor and acceptor groups. The use of nuclear magnetic resonance spectroscopy is an elegant way to identify and experimentally characterize Me/π interactions in proteins without the need for arbitrary geometric descriptions or pre-existing three-dimensional structures.