You wish to determine the sequence of a short peptide Cleava

You wish to determine the sequence of a short peptide. Cleavage with trypsin yields three smaller peptides with the sequences Leu–Glu, Gly–Tyr–Asn–Arg, and Gln–Ala–Phe– Val–Lys. Cleavage with chymotrypsin yields three peptides with the sequences Gln–Ala–Phe, Asn–Arg–Leu–Glu, and Val–Lys–Gly–Tyr. What is the sequence of the intact peptide?

Solution

The intact protein should be

Gln-Ala-Phe-Val-Lys-Gly-Tyr-Asn-Arg-Leu-Gly

Now if we observe the segments from chymotrypsin digestion, we can understand that Asn-Arg-leu-glu should be together , Val-lys-gly-Tyr should also be together and Gln-Ala-Phe should also be together. Now looking at trypsin digested parts, Gln-Ala-Phe should continue with Val-Lys which again should continue as Gly-Tyr (as all four amino acid should be together observed from chymotrypsin digestion. Now again from trypsin digested parts, Gly-Tyr should continue as Asn-Arg which again should be with Leu-Gly.