Analysis of sequence requirements for protein tyrosine sulfation.

We analyzed sequences surrounding known tyrosine sulfation sites to determine the characteristics that distinguish these sites from those that do not undergo sulfation. Tests evaluated the number and position of acidic, basic, hydrophobic, and small amino acids, as well as disulfide and N-glycosylation (sugar) sites. We determined that composition-based tests that select close to 100% of known tyrosine sulfation sites reject 97% of the non-sulfated tyrosines. The acidic test, by far the most selective, eliminated 95% of the non-sulfated tyrosine residues and none of the sulfated tyrosines. Including the basic, hydrophobic, and disulfide tests increased the elimination rate to 97%. Whereas no position flanking the tyrosine residues had the same amino acid always present, imperfectly conserved amino acids found in some positions will improve the specificity of the tests.