Abstract
Collagen is an important structural component of tissues in animals. It has an unique right-handed triple helix consisted of three left-handed polyproline II like chains which are composed of X-Y-Gly repeats in the sequence. TypeⅠcollagen, a heterotrimer, is the most abundant form, and thus using heterotrimeric helices can be more appropriate to mimic nature collagen. In this work, we used cation-π interactions to assist collagen-related peptides to fold into heterotrimers. CD and NMR measurements indicate that (POGPRG)3(POG) & (POGFOG)3(POG), (POGPRG)3(POG) & (POGFOG)3(POG) & (POG)7 mixed peptide solution could form a single heterotrimeric helices with Tm values of 26 and 27.5 ºC respectively, and no homotrimers were found. The results demonstrate that heterotrimers could be formed by interchain cation-π interactions. We have previously shown that terminal cation-π interactions can promote RG(POG)10F to rapidly assemble into fibrils. Here we further synthesized (POG)4(PRG)(FOG)(POG)4, (POG)3(PRG)(POG)2(FOG)(POG)3, (POG)2(PRG) (POG)4(FOG)(POG)2, and RG(POG)3(PRG)(POG)2(FOG)(POG)3F to study the position dependent effects of cation-π interactions on their self-assembly process. Turbility and dynamic light scattering measurements showed that such designs and arrangements do not significantly promote the assembly process. The results imply that the PRG and FOG triplets in place of POG in the middle of a collagen related peptide may impose steric effects through the bulky side chains of arginine and phenylalanine residues, which prevent the formation of strong cation-π interactions and retard the packing between collagen triple helices.