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1-a) The peptide bond cleaved by ETA is located on the amino-side of Ser and Thr residues.

Question

Recently, scientists have demonstrated that several chemicals can be used for the selective cleavage of peptide bonds in proteins. For example, ethyl trifluoroacetate (ETA) selectively cleaves the peptide bond located on the amino-side of Ser and Thr residues. Similarly, pentafluoropropionic acid (PFPA) selectively cleaves the peptide bonds located on the carboxyl-side of Asp residues. The α-melanocyte stimulating hormone is a short peptide whose sequence is: NH2-SYSMEHFRWGKPV-COOH. The peptide was submitted to chemical cleavage with ETA and the products of cleavage were sequenced by Edman degradation. 1-a) Predict the sequence of all the peptides formed by chemical cleavage. 1-b) The HPLC profiles (Figure [1]) show the derivatized amino acids produced after each round of Edman degradation. Is your previous prediction confirmed by these profiles? Briefly explain. The heat shock protein tetradecapeptide has the following sequence: NH2-CLNROLSSGVSEIR-COOH. This protein was treated with ETA and the cleavage fragments were analyzed by MALDI. 2-a) Predict the sequence of all the cleaved peptides (assuming complete cleavage). 2-b) The MALDI spectrum (Figure 2) shows that only peaks were produced. Identify the sequence of these peptides using their measured mass and the table of masses that you got in one of your lecture handouts. Note: One peak may be produced by a post-translationally modified form of the uncleaved peptide. Question 3: The heat shock tetradecapeptide was also treated with PFPA and 15% of the original peptide (Mass: 1642 Da) was converted into a smaller peptide (mass: 1562.8 Da). 3-a) Did you expect any cleavage with PFPA? Briefly explain. 3-b) Provide an explanation for this observation using the mass difference between the original and the smaller peptide and what you have learned in class about protein phosphorylation. 3-c) Suggest one method to confirm your hypothesis.

Recently, scientists have demonstrated that several chemicals can be used for the selective cleavage of peptide bonds in proteins. For example, ethyl trifluoroacetate (ETA) selectively cleaves the peptide bond located on the amino-side of Ser and Thr residues. Similarly, pentafluoropropionic acid (PFPA) selectively cleaves the peptide bonds located on the carboxyl-side of Asp residues.

The α-melanocyte stimulating hormone is a short peptide whose sequence is: NH2-SYSMEHFRWGKPV-COOH. The peptide was submitted to chemical cleavage with ETA and the products of cleavage were sequenced by Edman degradation.

1-a) Predict the sequence of all the peptides formed by chemical cleavage.
1-b) The HPLC profiles (Figure [1]) show the derivatized amino acids produced after each round of Edman degradation. Is your previous prediction confirmed by these profiles? Briefly explain.

The heat shock protein tetradecapeptide has the following sequence: NH2-CLNROLSSGVSEIR-COOH. This protein was treated with ETA and the cleavage fragments were analyzed by MALDI.

2-a) Predict the sequence of all the cleaved peptides (assuming complete cleavage).
2-b) The MALDI spectrum (Figure 2) shows that only peaks were produced. Identify the sequence of these peptides using their measured mass and the table of masses that you got in one of your lecture handouts. Note: One peak may be produced by a post-translationally modified form of the uncleaved peptide.

Question 3: The heat shock tetradecapeptide was also treated with PFPA and 15% of the original peptide (Mass: 1642 Da) was converted into a smaller peptide (mass: 1562.8 Da).

3-a) Did you expect any cleavage with PFPA? Briefly explain.
3-b) Provide an explanation for this observation using the mass difference between the original and the smaller peptide and what you have learned in class about protein phosphorylation.
3-c) Suggest one method to confirm your hypothesis.

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