Abstract
Collagen is a right-handed triple helix, and each helix is a left-handed polyproline type II structure containing many (X-Y-Gly) repeats. Many natural collagens consist of two or three different peptide chains. Type I collagen, the most abundant protein in the human body, is an AAB-type heterotrimer. Many forces were shown to have great contributions to collagen triple helix stability. Cation-π interaction, one of the forces, was found to be important in our previous studies. In this work, we prepared the collagen-mimetic peptides containing cationic or aromatic residues by incorporating Lys or Phe into the C-terminal end of the peptide chains. We attempted to use cation-π interactions to assist the folding of heterotrimers. Circular dichroism (CD), differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR) measurements showed that the cation-π interactions could effectively induced the formation of AAB-type heterotrimers. Compared to the results of Arg-containing CR3/CF3 series, (CK3)2(CF3)1 heterotrimers were less stable due to the weaker cation-π interactions between Lys and Phe. In addition, we prepared CR3_Sar and CK3_Sar in which a Gly residue near the center of CR3 and CK3 was substituted to sarcosine (Sar). Our results revealed that CR3_Sar could form homotrimers and AAB-type heterotrimers with CF3. The existence of cation-π interactions between chains has been confirmed by NMR measurements. Due to the weaker cation-π interactions between Lys and Phe, CK3_Sar, by contrast, could form neither homotrimers nor AAB-type heterotrimers with CF3.