The DQ-HN[CACB] and DQ-HN(CO)[CACB] sequences with evolution of double quantum Calpha-Cbeta coherences

Protein resonance assignment by solid-state NMR based on 1H-detected 13C double-quantum spectroscopy at fast MAS

Solid-state NMR spectroscopy is a powerful technique to study insoluble and non-crystalline proteins and protein complexes at atomic resolution. The development of proton (¹H) detection at fast magic-angle spinning (MAS) has considerably increased the analytical capabilities of the technique, enabling the acquisition of ¹H-detected fingerprint experiments in few hours. Here an approach based on double-quantum (DQ) ¹³C spectroscopy, detected on ¹H, is proposed for fast MAS regime (> 60 kHz) to perform the sequential assignment of insoluble proteins of small size, without any specific deuteration requirement. By combining two three-dimensional ¹H detected experiments correlating a ¹³C DQ dimension respectively to its intra-residue and sequential ¹⁵ N-¹H pairs, a sequential walk through DQ (Ca + CO) resonance is obtained. The approach takes advantage of fast MAS to achieve an efficient sensitivity and the addition of a DQ dimension provides spectral features useful for the resonance assignment process.

Principles and applications of GFT projection NMR spectroscopy

The two defining features of G-matrix Fourier transform (GFT) projection NMR spectroscopy are (i) repeated joint sampling of several indirect chemical shift evolution periods of a multidimensional NMR experiment so that transfer amplitudes are generated which are proportional to all possible permutations of cosine and sine modulations of the individual shifts, and (ii) linear combination of the subspectra resulting from such repeated joint sampling in the time or frequency domain which yields edited subspectra containing signals encoding phase-sensitively detected linear combinations of the jointly sampled shifts. This review sketches the underlying principles of GFT NMR and outlines its relation to further developments such as the reconstruction of multidimensional NMR spectra.