Projection-reconstruction of three-dimensional NMR spectra.

When three-dimensional NMR spectra are presented as two stereoscopic images, they create a convincing three-dimensional impression for the viewer. In an extension of this principle, we record plane projections of a three-dimensional spectrum at different angles, and use this limited information to reconstruct the entire spectrum. Projections onto different skew planes are derived by Fourier transformation of signals acquired while the two evolution parameters are incremented simultaneously at different rates. By limiting the amount of data gathering, this offers an appreciable economy of instrument time. Normally two to six different projections suffice, depending on the complexity of the spectra. There is an order-of-magnitude speed advantage over the conventional methodology, where both evolution dimensions must be explored independently. Results are presented for reconstructed HNCA and HN(CO)CA spectra of ubiquitin and the HNCO spectrum of a 187-residue protein HasA.