Question

A protein biochemist attempted to determine the amino acid sequence of a decapeptide. Use the results from the trypsin, chymotrypsin, and cyanogen bromide treatments to suggest the amino acid sequence of this decapeptide. Trypsin digestion gave two fragments with the following residues (not in order): T1: Ala, Arg, Phe, Pro, Thr, Trp, Tyr T2: Lys, Met, Val Chymotrypsin digestion gave three fragments with the following residues (not in order): CT1: Ala, Arg, Phe, Pro CT2: Thr, Trp CT3: Lys, Met, Tyr, Val N‑terminal analysis of the CT1 tetrapeptide indicated that the N‑terminal amino acid was Ala. The cyanogen bromide gave only one single amino acid, methionine, and a nonapeptide. What is a possible sequence of the decapeptide? Use three‑letter abbreviations in your answer, and add a dash between each residue.

Answer 1

The possible sequence of the decapeptide is Met-Val-Lys-Tyr-Thr-Trp-Ala-Arg-Pro-Phe.

Step-by-step explanation:

The cyanogen bromide cleaves the carboxyl end of Met (methionine and non-peptide). Trypsin cleaves on the C-terminal of Arg and Lys, however, not on the N-terminal of Pro, which signifies that Lys is the last amino acid in T2. Hence, Met-Val-Lys----. The middle part of the sequence can be predicted from the digestion done by chymotrypsin.

The chymotrypsin cleaves on the C terminal of Phe, Trp, Tyr, however, not on the N side of Pro. CT3 exhibit Lys, Met, Tyr, Val, as Met-Val and Tyr are the initial three amino acids, therefore, Tyr must be the fourth one. Now the sequence will be Met-Val-Lys-Tyr...

CT1 possesses Ala, Arg, Phe, Pro, as chymotrypsin cleaves the C side of the Phe, thus, the last amino acid should be Phe. Also, CT1 has Ala as the first amino acid. Also, trypsin does not cleave on the N-end of Pro. Thus, the sequence of CT1 strands will be Ala-Arg-Pro-Phe.

In CT2, chymotrypsin cleaves on the C-side of trp. Thus, the sequence of CT2 strands as Thr-Trp is found in the middle. Thus, the whole sequence of the decapeptide strand will be:

Met-Val-Lys-Tyr-Thr-Trp-Ala-Arg-Pro-Phe.