Question

CASE 6. A Collection of Collagen Cases Case 2 A group of investigators synthesized a series of collagen-like peptides each containing 30 amino acid residues in order to study the important interactions among the three chains in the triple helix. The following peptides were synthesized: (1) (Pro-Hyp-Gly)., (2) (Pro-Hyp-Gly).-Glu-Lys-Gly-(Pro-Hyp- Gly), and (3) Gly-Lys-Hyp-Gly-Glu-Hyp-Gly-Pro-Lys-Gly-Asp-Ala-(Gly-Ala-Hyp),-(Gly-Pro-Hyp),GV. These peptides are abbreviated (1) (POG)... (2) EK-containing peptide and (3) T3-487 in the table below. (Note that "0" is the one-letter abbreviation for hydroxyproline.) Table 6-2:Stability of three collagen-like peptides, Peptide T°C Forms trimers? Imino acid content (1) (POG), yes 67% pH-1 pH = 7 pH = 13 (2) EK-containing peptide yes 60% pH = 1 pH-7 pH - 13 pH-1 pH = 7 pH-13 (3) T3-487 yes 41% 18 26 19 (a) Rank the stability of the three collagen-like peptides (POG).., EK-containing peptide and T3-487 at pH = 7. What is the reason for the observed stability? (b) Compare the T. values of T3-487 at the various pH values. At what pH does T3-487 have a maximum T. value? What interactions are primarily responsible for this? (C) Compare the T, values of (POG), at the various pH values. Why is there less of a difference of T. values at different pH values for (POG), than for T3-487? (d) Consider the answers to the above questions. Which factor is more important in stabilizing the structure of the collagen-like peptides?

Answer 1

Solution :

a) The three collagen like peptides are ranked in increasing order of stability is mentioned below

T3-487 < EK containing peptides < (POG)₁₀ . The stability recorded here is due to its amino acid contents, Hydroxyproline is highly present in these amino acids and it modulates the thermal stability of this peptides by increasing due to its Stereoelectronic effects.

b) By comparing the T_m values of T3-487 at the various pH values, these are low at 18⁰C at low pH1 and also decreases at 19^oC at high pH13 and the stability is higher at 26^oC at pH7. The peptide has maximum T_m 26^oC results in higher levels of H- bond interactions possible near physiological pH present in Peptide T3-487. This assumption explains the structural importance of collagen like peptides in their funtions at physiological pH in body.

c)   The T_m values are comparatively closer at different pH than T3-487 in (POG)₁₀  are as follows

pH 1 - 61^oC >    pH 13 - 60^oC > pH 7 - 58^oC . Here the differences between T_m values are significantly less at various pH values in (POG)₁₀ because of the similarity in content of the peptide. In (POG)₁₀ 67% of the content is imino acid ( 33.3% Pro and 33.3% of Hyp, a derivative of Pro). So similar T_m values are observed in the peptide homology.

d) The amino acid content and their non-covalent interactions play a most significant role in stabilizing the structure of the collagen like peptides .This factor is observed from the above answers.