Acetyl-terminated and template-assembled collagen-based polypeptides composed of Gly-Pro-Hyp sequences .2. Synthesis and conformational analysis by circular dichroism, ultraviolet absorbance, and optical rotation

Template-assembled collagen-based polypeptides KTA-[Gly-(Gly-Pro-Hyp)(n)-NH2](3) (n = 1, 3, 5, 6; KTA is cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid, also known as the Kemp triacid) and acetyl-terminated single-chain collagen-based analogs Ac-(Gly-Pro-Hyp)(n)-NH2 (n = 1, 3, 5, 6, 9) were synthesized by solid phase segment condensation methods. The triple-helical propensities of these collagen analogs were investigated using circular dichroism, ultraviolet absorbance, optical rotation, and nuclear magnetic resonance measurements. The acetyl analogs, Ac-(Gly-Pro-Hyp)(n)-NH2(n = 6, 9), assume a stable triple-helical conformation in H2O (0.2 mg/mL) at room temperature. By contrast, Ac-(Gly-Pro-Hyp)(5)-NH2 adopts a triple-helical conformation in H2O only below 18 degrees C at a concentration of 0.2 mg/mL. For the template-assembled collagen analogs, results show that KTA-[Gly-(Gly-Pro-Hyp)(n)-NH2](3) (n = 5, 6) peptides form triple-helical structures which have melting temperatures above 70 degrees C in H2O. These melting temperatures are much higher than those of the corresponding acetyl analogs, demonstrating the significant triple-helix-stabilizing effects of the KTA template. In addition, the KTA template facilitates triple-helical structures by dramatically accelerating triple-helix formation.