Orphan Spin Polarization: A Catalyst for High-Throughput Solid-State NMR Spectroscopy of Proteins

Magic-angle spinning solid-state NMR (MAS ssNMR) spectroscopy is a powerful method for structure determination of biomacromolecules that are recalcitrant to crystallization (membrane proteins and fibrils). Relatively low sensitivity and poor resolution of protein samples require long acquisition times for multidimensional ssNMR experiments. Conventional multidimensional ssNMR pulse sequences acquire one experiment at a time, which is time consuming and often discards orphan (unused) spin operators. Here, we describe our recent progress in the development of multiple acquisition ssNMR methods for protein structure determination. A family of experiments called polarization optimized experiments (POE) was designed, in which we utilized the orphan spin operators that are discarded in classical NMR experiments to recover them and acquire simultaneously multiple 2D and 3D experiments using conventional probes and spectrometers with one receiver. Three strategies namely, DUMAS, MEIOSIS, and MAeSTOSO were used for the concatenation of various 2D and 3D pulse sequences. These methods open up new avenues for reducing the acquisition time of multidimensional experiments for biomolecular ssNMR spectroscopy.