Assigning the NMR spectra of aromatic amino acids in proteins: analysis of two Ets pointed domains.

The measurement of interproton nuclear Overhauser enhancements (NOEs) and dihedral angle restraints of aromatic amino acids is a critical step towards determining the structure of a protein. The complete assignment of the resonances from aromatic rings and the subsequent resolution and identification of their associated NOEs, however, can be a difficult task. Shown here is a strategy for assigning the 1H, 13C, and 15N signals from the aromatic side chains of histidine, tryptophan, tyrosine, and phenylalanine using a suite of homo- and hetero-nuclear scalar and NOE correlation experiments, as well as selective deuterium isotope labelling. In addition, a comparison of NOE information obtained from homonuclear NOE spectroscopy (NOESY) and 13C-edited NOESY-heteronuclear single quantum correlation experiments indicates that high-resolution homonuclear two-dimensional NOESY spectra of selectively deuterated proteins are invaluable for obtaining distance restraints to the aromatic residues.