Measuring the 3J HNHa coupling by a simple 2D-intra-HNCA IP/AP-E.COSY with simultaneous encoding of 15N chemical shift and 1J HaCa evolution.

The 3J coupling values are commonly used in biomolecular NMR to extract structural information. Here we present a novel intra HNCA IP/AP E.COSY pulse sequence that allows to measure 3J HNHa coupling constants by a simple and rapid two-dimensional 1H-15N correlation experiment where the 15N frequency is encoded at the same time as the 1J HaCa coupling evolution. The advantage with respect to the conventional 3D HNCA E.COSY pulse sequence is the dimensionality reduction to a simple 2D experiment, which decreases acquisition time and facilitates data analysis. The performance of this new experiment is demonstrated with an ubiquitin sample at 500 MHz.