A new strategy for backbone resonance assignment in large proteins using a MQ-HACACO experiment.

A new strategy of backbone resonance assignment is proposed based on a combination of the most sensitive TROSY-type triple resonance experiments such as TROSY-HNCA and TROSY-HNCO with a new 3D multiple-quantum HACACO experiment. The favourable relaxation properties of the multiple-quantum coherences and signal detection using the (13)C' antiphase coherences optimize the performance of the proposed experiment for application to larger proteins. In addition to the (1)H(N), (15)N,(13)C(alpha) and (13)C' chemical shifts the 3D multiple-quantum HACACO experiment provides assignment for the (1)H(alpha) resonances in constrast to previously proposed experiments for large proteins. The strategy is demonstrated with the 44 kDa uniformly (15)N,(13)C-labeled and fractionally 35% deuterated trimeric B. subtilis Chorismate Mutase measured at 20 degrees C and 9 degrees C. Measurements at the lower temperature indicate that the new strategy can be applied to even larger proteins with molecular weights up to 80 kDa.