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

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