Question

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?

Short answer

The intact peptide will have the sequence:

Ile-Ala-Tyr-Val-Arg-Gly-trp-asn-Lys-Leu-Glu

Step-by-step solution

Protein sequencing

For sequencing a protein, the protein must first be broken down into small fragments.Endopeptidases like pepsin, trypsin, chymotrypsin, etc. can be used to cleave the peptide into smaller fragments. The peptide is cleaved using two different peptidases to yield two different sets of fragments. Then the amino acid sequence of each of the fragments is determined. After this, the fragments are overlapped to reconstruct the sequence of the whole polypeptide.

Explanation

The small peptides obtained through cleavage with trypsin and chymotrypsin are overlapped to determine the sequence of the polypeptide.

Thus, the sequence of the intact polypeptide is:

Ile-Ala-Tyr-Val-Arg-Gly-trp-asn-Lys-Leu-Glu