A 15n-filtered 2D 1H TOCSY experiment for assignment of aromatic ring resonances and selective identification of tyrosine ring resonances in proteins: Description and application to Photoactive Yellow Protein

A new method to selectively detect the ring resonances of the aromatic residues in 15N-labelled proteins is presented. The experiment consists of a 2D 1H TOCSY sequence withremoval of the amide signals via 15N-filtering. Experiments are acquired in the absence andpresence of water inversion; combining the two spectra allows selective observation of thetyrosine ring resonances and enables the identification of their delta andepsilon ring protons. The experiment is demonstrated on a 15N-labelled sample of Photoactive Yellow Protein and isshown to give good selectivity for tyrosine ring resonances under a wide range oftemperatures and pH values.