Sulphation of tyrosine residues-a widespread modification of proteins.

Abstract

Of the many known covalent modifications of proteins1, few have been recognized as widespread. Among these modifications, protein phosphorylation has been extensively studied2–4. Recently, phosphorylation of tyrosine residues has been implicated in regulatory events such as cell transformation and hormone-induced cell growth5–7. The present study explores the possibility that another modification of tyrosine residues in proteins, tyrosine sulphation, may be widespread. This modification is particularly interesting because of the molecular resemblance of tyrosine-O-sulphate and tyrosine-O-phosphate. Protein sulphation on tyrosine residues was found to occur in all cell types in culture and all tissues in situ so far examined. Moreover, for each cell type and tissue, proteins containing tyrosine-O-sulphate were found in distinct electrophoretic patterns throughout the molecular weight range studied. Thus, protein sulphation on tyrosine residues appears to be a widespread covalent modification, and may have an important role in cell function.