A protein biochemist attempted to determine the amino acid sequence of a decapep

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, containing 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.

Explanation / Answer

The primary sturcture can be derived by using the following data facts:

Let Rn and Rn-1 denote the functional groups attached to the carbon next to alpha carbon on its right and left respectively.

1. For trypsin digestion, Rn-1 must be negatively charged and Rn must not be proline. Also, tryosine recognises C terminsl lysine.

2.For chymotrypsin digestion, Rn-1 is a bulky residue,like tyrosine,tryptophan or phenylalanine.

3.CNBr treatment recognises C terminal to Methionine.

So the decapeptide has the primary structure,

N Ala, Arg, Phe, Pro, Thr, Trp, Tyr, Val, Lys, Met C

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