Fast reconstruction of four-dimensional NMR spectra from plane projections.

Four-dimensional NMR spectroscopy can be speeded up by a large factor by a projection-reconstruction technique related to that used in X-ray tomography. The limited amount of information recorded in a few suitably-tilted projection planes suffices to recreate the entire four-dimensional spectrum. The method is demonstrated by reference to the 500 MHz spectrum of 1 millimolar aqueous solution of ubiquitin by dispersing the responses of the three-dimensional HNCO spectrum into the C(alpha) dimension of a four-dimensional HNCOCA spectrum obtained by projection-reconstruction.