BEST and SOFAST experiments for resonance assignment of histidine and tyrosine side chains in 13C/15N labeled proteins.

Aromatic amino-acid side chains are essential components for the structure and function of proteins. We present herein a set of NMR experiments for time-efficient resonance assignment of histidine and tyrosine side chains in uniformly 13C/15N-labeled proteins. The use of band-selective 13C pulses allows to deal with linear chains of coupled spins, thus avoiding signal loss that occurs in branched spin systems during coherence transfer. Furthermore, our pulse schemes make use of longitudinal 1H relaxation enhancement, Ernst-angle excitation, and simultaneous detection of 1H and 13C steady-state polarization to achieve significant signal enhancements.