The Local Environment of Iron Determines the Rupture Force of Rubredoxin and Not Hydrogen Bond Networks

The surprisingly low rupture force and remarkable mechanical anisotropy of rubredoxin have been known for several years. Exploiting the first combination of steered molecular dynamics and the quantum chemical Judgement of Energy DIstribution (JEDI) analysis, the distribution of strain energy in the central part of rubredoxin is elucidated in real-time with unprecedented detail. In contrast to common belief that hydrogen bonds between neighboring amino acid backbones and the sulfur atoms of the central FeS4 unit in rubredoxin determine the low mechanical resistance of the protein, we demonstrate that structural anisotropy as well as the contribution of angle bendings in the FeS4 unit are instead the key factors responsible for the low rupture force in rubredoxin. In addition to clarifying the structural basis for the mechanical unfolding of an important metalloprotein, this study paves the way for in-depth investigations of an intriguing new class of mechanophores involving metal ions.