Sparsely-sampled, high-resolution 4-D omit spectra for detection and assignment of intermolecular NOEs of protein complexes.

Unambiguous detection and assignment of intermolecular NOEs are essential for structure determination of protein complexes by NMR. Such information has traditionally been obtained with 3-D half-filtered experiments, where scalar coupling-based purging of intramolecular signals allows for selective detection of intermolecular NOEs. However, due to the large variation of (1)JHC scalar couplings and limited chemical shift dispersion in the indirect proton dimension, it is difficult to obtain reliable and complete assignments of interfacial NOEs. Here, we demonstrate a strategy that combines selective labeling and high-resolution 4-D NOE spectroscopy with sparse sampling for reliable identification and assignment of intermolecular NOEs. Spectral subtraction of component-labeled complexes from a uniformly-labeled protein complex yields an "omit" spectrum containing positive intermolecular NOEs with little signal degeneracy. Such a strategy can be broadly applied to unbiased detection, assignment and presentation of intermolecular NOEs of protein complexes.