(4,2)D projection-reconstruction experiments for protein backbone assignment:: Application to human carbonic anhydrase II and calbindin D28K

Projection -reconstruction NMR experiments have been shown to significantly reduce the acquisition time required to obtain protein backbone assignment data. To date, this concept has only been applied to smaller N-15/C-13-Iabeled proteins. Here, we show that projection- reconstruction NMR techniques can be extended to larger protonated and perdeuterated proteins. We present a suite of (4,2)D triple-resonance experiments for protein backbone assignment and a Hybrid Backprojection/Lower-Value algorithm for reconstructing data with relatively weak signal-to-noise ratios. In addition, we propose a sampling theorem and discuss its implication on the choice of projection angles. We demonstrate the efficacy of this approach using the 29 kDa protein, human carbonic anhydrase 11 and the 30 kDa protein, calbindin D-28K.