Amino acid selective 'unlabelling' for residue-specific NMR assignments inproteins

A novel methodology for sequence-specific resonance assignments in proteins , using amino acid selective 'unlabelling' is presented. The strategy is ba sed on selective unlabelling of amino acid residues in uniformly or fractio nally C-13 or/and N-15 labeled proteins, which simplify the multi-dimension al heteronuclear NMR spectra. This aids in sequence-specific resonance assi gnments of both backbone and side-chain nuclei, The methodology has been de monstrated by unlabelling Lys residues in a 15 kDa calcium-binding protein from Entamoeba histolytica (Eh-CaBP).