Affinity chromatography on immobilized anhydrotrypsin: general utility for selective isolation of C-terminal peptides from protease digests of proteins.

Recently we have succeeded in the efficient isolation of the C-terminal peptides from tryptic digests of the tail sheath protein (with C-terminal Gly) and the tube protein (with C-terminal Glu) of bacteriophage T4, by taking advantage of a unique property of immobilized anhydrotrypsin, that is, a strong specific affinity for peptides containing Arg or Lys residues at their C-termini. In this study, the utility of affinity chromatography on immobilized anhydrotrypsin was further demonstrated in the cases of Streptomyces subtilisin inhibitor (as a reduced and S-carboxymethylated form, with C-terminal Phe) and alpha 1-antitrypsin (with C-terminal Lys). By subjecting a tryptic digest of the former protein and a chymotryptic digest of the latter protein to the affinity chromatography, the C-terminal peptides were specifically recovered in the breakthrough fraction and in the adsorbed fraction, respectively. It was further shown that immobilized anhydrotrypsin can also adsorb peptides with C-terminal S-aminoethyl-Cys residues and exerts adsorptive ability even toward the peptides in solution containing urea at a high concentration if appropriate precautions are taken. These findings suggest the general utility of this simple method for C-terminal peptide isolation, which is extremely helpful for studies to confirm amino acid sequences deduced from nucleotide sequences of the cDNA (or genomic DNA) of proteins.