Intraresidue HNCA and COHNCA experiments for protein backbone resonance assignment

Two novel experiments, intra-HNCA and intra-COHNCA, are presented for sequential backbone resonance assignment of (13)C, (15)N labeled proteins. The advantage with respect to conventional pulse schemes is the suppression of the sequential (15)N-->(13)C(alpha) coherence transfer pathway, which can be separately obtained from a HNCOCA correlation experiment. This results in a two-fold reduction of the number of detected correlation peaks. Spectral simplification is especially important for efficient automated assignment protocols as required in the context of high-throughput protein studies by NMR. The performance of the new experiments is demonstrated on an 18-kDa protein fragment of the E. coli sulfite reductase and compared to conventional techniques in terms of sensitivity and resolution.