A sample of an unknown peptide was divided into two aliquots.One Aliquot was tre

Question

A sample of an unknown peptide was divided into two aliquots.One Aliquot was treated with trypsin, and the other with cyanogenbromide. Given the following sequences (N-terminal to C-terminal)of the resulting fragments, deduce the sequence of the originalpolypeptide and write the primary structure in the space betweenN........C down below.               Trypsin treatment                Asn-Thr-Trp-Met-Ile-Lys               Gly-Tyr-Met-Gln-Phe               Val-Leu-Gly-Met-Ser-Arg               Cyanogen bromide treatment                Gln-Phe               Val-Leu-Gly-Met                Ile-Lys-Gly-Tyr-Met                Ser-Arg-Asn-Thr-Trp-Met N.............................................................................................C A sample of an unknown peptide was divided into two aliquots.One Aliquot was treated with trypsin, and the other with cyanogenbromide. Given the following sequences (N-terminal to C-terminal)of the resulting fragments, deduce the sequence of the originalpolypeptide and write the primary structure in the space betweenN........C down below.               Trypsin treatment                Asn-Thr-Trp-Met-Ile-Lys               Gly-Tyr-Met-Gln-Phe               Val-Leu-Gly-Met-Ser-Arg               Cyanogen bromide treatment                Gln-Phe               Val-Leu-Gly-Met                Ile-Lys-Gly-Tyr-Met                Ser-Arg-Asn-Thr-Trp-Met N.............................................................................................C

Explanation / Answer

The procedure is quite simple. From the trypsin treatment we get the followingfragments:             Asn-Thr-Trp-Met-Ile-Lys               Gly-Tyr-Met-Gln-Phe               Val-Leu-Gly-Met-Ser-Arg Trypsin is an enzyme which cleaves on the carboxyl end of theamino acids Lysine and Arginine. Here in these fragments we see that there is a fragment whichends with Phe. This indicates that this amino acid is the C-terminal aminoacid. To know the actual sequence of the peptide we go to theresults of the cyanogen bromide digestion products. From the CN treatment we get the following results:               Gln-Phe               Val-Leu-Gly-Met                Ile-Lys-Gly-Tyr-Met                Ser-Arg-Asn-Thr-Trp-Met We know that CN cleaves at the carboxyl end of the amino acidmethionine. As we can see, the peptides released all have Met except onefragment. This fragment also ends in Phe. So we can confirm that Phe is the C-terminal amino acid. To get to know the primary sequence we just compare theresults of the two digestion processes: From the CN treatment we know that Phe is the C-terminal amino acid. So comparing with the 2nd fragment of trypsin digestionwe get the following sequence: Gly-Tyr-Met-Gln-Phe Trypsin is an enzyme which cleaves on the carboxyl end of theamino acids Lysine and Arginine. Here in these fragments we see that there is a fragment whichends with Phe. This indicates that this amino acid is the C-terminal aminoacid. To know the actual sequence of the peptide we go to theresults of the cyanogen bromide digestion products. From the CN treatment we get the following results:               Gln-Phe               Val-Leu-Gly-Met                Ile-Lys-Gly-Tyr-Met                Ser-Arg-Asn-Thr-Trp-Met We know that CN cleaves at the carboxyl end of the amino acidmethionine. As we can see, the peptides released all have Met except onefragment. This fragment also ends in Phe. So we can confirm that Phe is the C-terminal amino acid. To get to know the primary sequence we just compare theresults of the two digestion processes: From the CN treatment we know that Phe is the C-terminal amino acid. So comparing with the 2nd fragment of trypsin digestionwe get the following sequence: Gly-Tyr-Met-Gln-Phe We know that CN cleaves at the carboxyl end of the amino acidmethionine. As we can see, the peptides released all have Met except onefragment. This fragment also ends in Phe. So we can confirm that Phe is the C-terminal amino acid. To get to know the primary sequence we just compare theresults of the two digestion processes: From the CN treatment we know that Phe is the C-terminal amino acid. So comparing with the 2nd fragment of trypsin digestionwe get the following sequence: Gly-Tyr-Met-Gln-Phe Next we observe the fragment Gly-Tyr-Met in the CN digestion results: WE see the sequence in the 3rd fragment.We also get thesequence of the amino acids before Gly. Ile-Lys-Gly-Tyr-Met. So now the present sequence of the fragment is Ile-Lys-Gly-Tyr-Met-Gln-Phe Now we search the results of the trypsin digestion for thissequence: Ile-Lys- We find it in the first sequence Asn-Thr-Trp-Met-Ile-Lys So now we know the amino acids before Ile. We now search for this sequence-- Asn-Thr-Trp-Met We search the CN digestion results: we get a match in the 4th fragment: Ser-Arg-Asn-Thr-Trp-Met WE now search for the sequence--Ser-Arg-Asn-Thr we search the trypsin results.we get a match in the thirdfragment. Val-Leu-Gly-Met-Ser-Arg so now we know that the N-terminal amino acid is Valine. The sequence of the whole peptide from N-terminal toC-terminal is as follows: N'---Val-Leu-Gly-Met-Ser-Arg-Asn-Thr-Trp-Met-Ile-Lys-Gly-Tyr-Met-Gln-Phe--C'

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