Chemical shift based editing of CH3 groups in fractionally $^{13}C$-labelled proteins using GFT (3,2)D CT-HCCH-COSY: stereospecific assignments of $CH_3$ groups of Val and Leu residues

Abstract

We propose a (3,2)D CT-HCCH-COSY experiment to rapidly collect the data and provide significant dispersion in the spectral region containing $^13$C-$1^H$ cross peaks of $CH_3$ groups belonging to Ala, Ile, Leu, Met, Thr and Val residues. This enables one to carry out chemical shift based editing and grouping of all the $^{13}C$-$^1H$ cross peaks of $CH_3$ groups belonging to Ala, Ile, Leu, Met, Thr and Val residues in fractionally (10%) $^{13}C$-labelled proteins, which in turn aids in the sequence-specific resonance assignments in general and side-chain resonance assignments in particular, in any given protein. Further, we demonstrate the utility of this experiment for stereospecific assignments of the pro-R and pro-S methyl groups belonging to the Leu and Val residues in fractionally (10%) $^{13}C-labelled proteins. The proposed experiment opens up a wide range of applications in resonance assignment strategies and structure determination of proteins