Effects of terminal tripeptide units on mechanical properties of collagen triple helices

Collagen, a vital protein that provides strength to various body tissues, has a triple helix structure containing three polypeptide chains. The chains are composed mostly of a tripeptide of glycine (G), proline (P), and hydroxyproline (O). Using molecular dynamics simulations and theoretical analysis, the study examines the mechanical response of collagen triple helix structures, made up of three different tripeptide units, when subjected to different fracture loading modes. The results show that collagen with GPO tripeptide units at their C-terminal are mechanically stronger than the POG and OGP units with a single amino acid frame shift. Our work shows that the N-terminal has less effect on collagen fracture than the C-terminal. The differences in mechanical response are explained by the heterogeneous rigidity of the amino acid backbone and the resulting shear lag effect near the terminal. The findings have potential applications in developing tough synthetic collagen for building materials and may stimulate further studies on the connection between terminal repeats and the mechanical–thermal behavior of other structural proteins such as silk, elastin, fibrin, and keratin.