ACETYL-TERMINATED AND TEMPLATE-ASSEMBLED COLLAGEN-BASED POLYPEPTIDES COMPOSED OF GLY-PRO-HYP SEQUENCES .2. SYNTHESIS AND CONFORMATIONAL-ANALYSIS BY CIRCULAR-DICHROISM, ULTRAVIOLET ABSORBENCY, AND OPTICAL-ROTATION

Template-assembled collagen-based polypeptides KTA-[Gly-(Gly-Pro-Hyp)( n)-NH2](3) (n = 1, 3, 5, 6; KTA is cis-1,3,5-trimethylcyclohexane-1,3, 5-tricarboxylic acid, also known as the Kemp triacid) and acetyl-termi nated single-chain collagen-based analogs Ac-(Gly-Pro-Hyp)(n)-NH2 (n = 1, 3, 5, 6, 9) were synthesized by solid phase segment condensation m ethods. The triple-helical propensities of these collagen analogs were investigated using circular dichroism, ultraviolet absorbance, optica l rotation, and nuclear magnetic resonance measurements. The acetyl an alogs, Ac-(Gly-Pro-Hyp)(n)-NH2(n = 6, 9), assume a stable triple-helic al conformation in H2O (0.2 mg/mL) at room temperature. By contrast, A c-(Gly-Pro-Hyp)(5)-NH2 adopts a triple-helical conformation in H2O onl y 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 ha ve melting temperatures above 70 degrees C in H2O. These melting tempe ratures are much higher than those of the corresponding acetyl analogs , demonstrating the significant triple-helix-stabilizing effects of th e KTA template. In addition, the KTA template facilitates triple-helic al structures by dramatically accelerating triple-helix formation.