Enzymatic labeling of arbitrary proteins.

This paper describes an enzymatic labeling technique (ELT), using transglutaminases. On the basis of the ELT, isotopic nuclei are easily incorporated into the gamma-carboxyamide groups of glutamine residues in arbitrary proteins, without changing their chemical structures. We have also shown that, by using ELT, protein aggregation was easily checked for NMR studies and that it can be applicable for the screening of weakly bound ligands for proteins. Owing to the simple preparation of the isotope-labeled proteins, ELT should be useful for speeding up various structural and functional analyses of arbitrary proteins.