Question

After undergoing complete hydrolysis, a polypeptide yields the following amino acids: Gly, Leu, Ala, Val, Ser, Thr. Partial hydrolysis yields the following fragments: Ser-Gly-Val, Thr-Val, Ala-Ser, Leu-Thr-Val, Gly-Val-Thr. An experiment using a marker establishes that Ala is the N-terminal amino acid. (a) Establish the amino acid sequence in this polypeptide. (b) What is the name of the polypeptide?

Short answer

The amino acid sequence in this polypeptide is Ala-Ser-Thr-Val-Ser-Gly-Val-Thr-Leu and the name of the polypeptide is alanyl-seryl-threonyl-valyl-seryl-glycyl-valyl-threonyl-leucine

Step-by-step solution

Recognizing the given fragments

We are given the five peptide fragments obtained through partial hydrolysis they are Ser-Gly-Val, Thr-Val, Ala-Ser, Leu-Thr-Val, Gly-Val-Thr. Now all these fragments are to be ordered in such a way that they align along the length of a sequence with overlaps providing the connections.

Arrange fragments to form a sequence

To piece these fragments together into a sequence, let's look for overlaps between the fragments. We know Ala must be the first amino acid since it has been stated as the N-terminal amino acid. From partial hydrolysis data, it is known that Ala is followed by Ser. Thr-Val seems to complete the sequence of Ala-Ser. Ser is followed by Gly-Val from the fragment Ser-Gly-Val. Lastly, Gly-Val-Thr connects with Leu-Thr to complete the sequence.

Confirm the sequence

Now we can formulate the amino acid sequence: It starts with Ala-Ser, which is connected to Thr-Val, in turn connected to Ser. This fragment is then connected to Gly-Val, which is connected to Thr-Leu. Therefore, the full peptide sequence is Ala-Ser-Thr-Val-Ser-Gly-Val-Thr-Leu.

Naming the Polypeptide

The polypeptide name is typically determined by the sequence of the amino acids. In this case, the polypeptide would simply be called: alanyl-seryl-threonyl-valyl-seryl-glycyl-valyl-threonyl-leucine