GFT NMR experiments for polypeptide backbone and ¹³C^β chemical shift assignment

(4,3)D, (5,3)D and (5,2)D GFT triple resonance NMR experiments are presented for polypeptide backbone and ¹³C^β resonance assignment of ¹⁵N/¹³ labeled proteins. The joint sampling of m = 2, 3 or 4 indirect chemical shift evolution periods of 4D and 5D NMR experiments yields the measurement of 2^m - 1 linear combinations of shifts. To obtain sequential assignments, these are matched in corresponding experiments delineating either intra or interresidue correlations. Hence, an increased set of matches is registered when compared to conventional approaches, and the 4D or 5D information allows one to efficiently break chemical shift degeneracy. Moreover, comparison of single-quantum chemical shifts obtained after a least squares fit using either the intra or the interresidue data demonstrates that GFT NMR warrants highly accurate shift measurements. The new features of GFT NMR based resonance assignment strategies promise to be of particular value for establishing automated protocols.