Question

After purification, the Edman reaction was used to sequence a dodecapeptide, yielding the following data: the C-terminal amino acid is isolcucine; the N-terminal amino acid is methionine; and the peptide fragments are Ala-Ala- Ile, Leu-Arg-Lys-Lys-Glu-Lys-Glu-Ala, Met-Gly-Leu, and Met-Phe-Pro-Met. What is the sequence of this peptide?

Short answer

The sequence of the given dodecapeptide is Met-Gly-Leu-Ala-Ala-Ile-Leu-Arg-Lys-Lys-Glu-Lys-Glu-Ile.

Step-by-step solution

Identify the N-terminal and C-terminal amino acids.

The given information tells us that the N-terminal amino acid is Methionine (Met) and the C-terminal amino acid is Isoleucine (Ile). Keep this information in mind as we put together the peptide sequence.

List the peptide fragments.

The peptide fragments given are: 1. Ala-Ala-Ile 2. Leu-Arg-Lys-Lys-Glu-Lys-Glu-Ala 3. Met-Gly-Leu 4. Met-Phe-Pro-Met

Align the peptide fragments.

Since the N-terminal amino acid is Met, we can start by aligning fragments that start with Met, which are fragments 3 and 4: 1. Met-Gly-Leu 2. Met-Phe-Pro-Met

Join the fragments.

Notice that fragment 1 (Ala-Ala-Ile) can be attached to fragment 3 (Met-Gly-Leu) to get Met-Gly-Leu-Ala-Ala-Ile. Now, attach fragment 2 (Leu-Arg-Lys-Lys-Glu-Lys-Glu-Ala) to this new sequence and remember that the C-terminal amino acid is Ile. The sequence we have so far is: Met-Gly-Leu-Ala-Ala-Ile-Leu-Arg-Lys-Lys-Glu-Lys-Glu-Ala But we know that the C-terminal amino acid is Isoleucine (Ile), so we need to adjust the sequence by replacing the last Ala-Ala-Ile part with Ile, to match the given information. Therefore, the correct peptide sequence is:

Final peptide sequence.

Met-Gly-Leu-Ala-Ala-Ile-Leu-Arg-Lys-Lys-Glu-Lys-Glu-Ile This is the sequence of the given dodecapeptide.