Date of Award
Spring 5-3-2024
Document Type
Thesis
Degree Name
Master of Arts (MA)
Department
Chemistry
First Advisor
Yujia Xu
Second Advisor
Wayne Harding
Academic Program Adviser
YuJia Xu
Abstract
Collagen mimetic peptides are used broadly for collagen research and biomedical applications. Unlike the synthetic peptides obtained by solid phase chemical synthesis, recombinant peptides have more than 100 amino acid residues in length and are expressed in E. coli using designed genes. These longer peptides can offer improved, more native-like functions of native collagen for biomedical applications. One major challenge is the intrinsically low stability of native collagen, which has a melting temperature just above the physiological temperature of the organism. To understand how to enhance the thermostability of the peptides, I investigated the effects of amino acid sequences on the stability of the triple helix using peptides modeling a 60-residue segment from the ɑ1 or ɑ2 chains of the type I collagen of the connective tissues. Type I collagen is the predominant form of collagen in connective tissues, and its natural form is a heterotrimer composed of two ɑ1 chains and one ɑ2 chain. Despite the high sequence homology, the homotrimeric form of the ɑ1 chain is thermally more stable than that of the ɑ2 chain by about 2.5℃. This variation in thermal stability persists in a wide range of pH and is independent of ionic strength. A point mutation replacing an Ile residue by a Pro in the ɑ2 peptide increased the thermal stability by about 2.5 ℃. The addition of Gly-Pro-Pro sequences at the N- and C-termini of the peptides also increased the thermal stability. The inclusion of residues that are purported to form the interchain salt bridges, however, failed to improve thermal stability in both the ɑ2 and the ɑ1 peptides. The latter finding contradicts the results of synthesized peptides showing a 15 °C improvement in thermal stability by the interchain salt bridges. Taken together, my study shows that the stabilizing effects of amino acid residues are highly dependent on the length of the peptides and the sequence context. Furthermore, the impacts of individual residues appear to diminish as the peptide becomes longer, possibly due to the trade-off between entropy loss and enthalpy gain of protein folding.
Recommended Citation
Xu, Zhenxun, "A study of the effects of an amino acid residue on the thermal stability of a collagen triple helix in varied sequence context, pH, and ionic strength of the buffer" (2024). CUNY Academic Works.
https://academicworks.cuny.edu/hc_sas_etds/1140