Intraresidual HNCA: an experiment for correlating only intraresidual backbone resonances.

Resonance overlap in 13Calpha-dimension can seriously deteriorate sequential assignment of proteins, especially in the case of highly alpha helical or partially unfolded structures. In this paper, two novel triple-resonance experiments, for obtaining solely intraresidual HN, N, Calpha correlations, are introduced. The proposed experiments are complementary to the conventional HN(CO)CA experiment, and can be utilized for the sequential assignment of 15N/13C/(2H)-labeled proteins. Coherence transfer efficiency of the new experiment is comparable to the conventional HNCA experiment on proteins with sufficiently long 15N transverse relaxation time. These new coherence transfer schemes are also very useful building blocks for experiments gathering structural information, such as J-couplings, exclusively on the intraresidual alpha carbon. Experimental assessment is demonstrated on ubiquitin at 600 1H MHz.