Asymptotic strength limit of hydrogen-bond assemblies in proteins at vanishing pulling rates.

We develop a fracture-mechanics-based theoretical framework that considers the free energy competition between entropic elasticity of polypeptide chains and rupture of peptide hydrogen bonds, which we use here to provide an explanation for the intrinsic strength limit of protein domains at vanishing rates. Our analysis predicts that individual protein domains stabilized only by hydrogen bonds cannot exhibit rupture forces larger than approximately 200 pN in the asymptotic limit. This result explains earlier experimental and computational observations that indicate an asymptotical strength limit at vanishing pulling rates.