Answer the following questions regarding the polypeptides shown below.Note that

Question

Answer the following questions regarding the polypeptides shown below.Note that Hyp stands for hydroxyproline – an amino acid formed by the vitamin-C dependent post-translational modification of proline.

Which polypeptide will most likely form a disulfide bond within the length of this peptide? What type of chemistry is involved in the formation of a disulfide bond – acid/base, redox or precipitation?

Which polypeptide will most likely be found in a collagen helix? What intermolecular forces are most important in stabilizing this structure? What do you expect for typical psi (y) and phi (f) angles for this type of structure?

Which polypeptide will have the lowest pI? Show your calculation.What does the pI tell you about the chemical and physical characteristics of this peptide?

Will the polypeptide in “c” be most easily separated from the other polypeptides by cation-exchange or anion-exchange chromatography? What pH would be best for this separation and why?

Which polypeptide will most likely be part of a membrane-spanning region of an integral membrane protein? If in the core of the membrane this peptide forms a classic a-helix and a typical membrane width is 30 angstroms, does this peptide have enough amino acids to span the membrane? Show your calculation as justification for your answer.

Answer the following questions regarding the polypeptides shown below. Note that Hyp stands for hydroxyproline an amino acid formed by the vitamin-C dependent post-translational modification of proline (1) Gly-Ile-Phe-Leu-Ile-Ile-Trp-Gly-Val-Val-Ala-Tyr-Val-Ile-Gly-Trp-Ile-Leu-Leu-Ile (2) Gly-Pro-Hyp-Gly-Pro-Met-Gly-Pro-Ser-Gly-Pro-Arg-Gly-Pro-Hyp-Gly-Pro-Hyp-Gly (3) Gly-Met-Asn-Pro-Gly-Asp-Cys-Gly-Glu-Pro-Ala-His-Val-Asp-Asp-Tyr-Pro-Leu-Leu (4) Gly-Met-Trp-Pro-Lys-Met-Cys-Gly-Arg-Pro-Ala-His-Val-Arg-Lys-Tyr-Cys-Leu-Leu a. Which polypeptide will most likely form a disulfide bond within the length of this peptide? What type of chemistry is involved in the formation of a disulfide bond - acid/base, redox or precptation? b. Which polypeptide will most likely be found in a collagen helix? What intermolecular forces are most important in stabilizing this structure? What do you expect for typical psi (v) and phi (O) angles for this type of structure? Which polypeptide will have the lowest pl? Show your calculation. What does the pl tell you about the chemical and physical characteristics of this peptide? d. Will the polypeptide in "c be most easily separated from the other polypeptides by cation why? exchange or anion-exchange chromatography? What pH would be best for this separation and Which polypeptide will most likely be part of a membrane-spanning region of an integral membrane protein? If in the core of the membrane this peptide forms a classic -helix and a typical membrane width is 30 angstroms, does this peptide have enough amino acids to span the membrane? Show your calculation as justification for your answer

Explanation / Answer

(4) Disulfide bond formation requires participation of two cysteines. Only chain (4) has two cysteines in it. Disulfide bonds are covalent bonds formed by oxidation of sulfhydryl groups of two cysteines, the two oxidized cysteines are linked together. Thus the reaction is a redox reaction.

(2). Collagen is typically composed of repeated tripeptide Gly-Pro-Hyp. The polypeptide chain (2) has this repeat. The molecule is stabilized by interchain Hydrogen bonds. The psi and phi angles are expected to be 154 and -57.

(3). this polypeptide has a pI of 3.62, whereas the other chains have pI of 5.55 for peptide (1), 5.94 for peptide (2), 9.9 for peptide (4).

The peptide is best separated by anion-exchange resin. When the pH of buffer is higher than pI of the peptide of interest, the peptide will bear a negative charge, and can be attached to a positively charged anion exchange resin.

(1) It has more hydrophobic amino acids compared to any other polypeptide chain. Yes. The peptide can span the membrane. Each amino acid in an alpha helix has a pitch of 1.5 Ao. The polypeptide chain is composed of 20 amino acids, and so, the helix forms a pitch of 30 Ao.

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