Side-chain H and C resonance assignment in protonated/partially deuterated proteins using an improved 3D13C-detected HCC-TOCSY

We propose the use of 13C-detected 3D HCC-TOCSY experiments for assignment of 1H and 13C resonances in protonated and partially deuterated proteins. The experiments extend 2D C-13-start and C-13-observe TOCSY type experiments proposed earlier [J. Biomol. NMR 26 (2) (2003) 167]. Introduction of the third 1H dimension to 2D TOCSY: (i) reduces the peak overlap and (ii) increases the sensitivity per unit time, even for highly deuterated (>85%) protein samples, which makes this improved method an attractive tool for the side-chain H and C assignment of average sized proteins with natural isotope abundance as well as large partially deuterated proteins. The experiments are demonstrated with a 16 kDa 15N, 13C-labeled non-deuterated apo-CcmE and a 48 kDa uniformly 15N,13C-labeled and fractionally (∼90%) deuterated dimeric sFkpA. It is predicted that this method should be suitable for the assignment of methyl 13C and 1H chemical shifts of methyl protonated, highly deuterated and 13C-labeled proteins with even higher molecular weight.