Prestress in Protein Disulfide Bonds Tunes their Stabilities

Abstract

Disulfide bonds are ubiquitous covalent links in proteins. By providing a protein fold with additional structural constraints they can tune protein stability and function. We find disulfide bonds to exhibit a varying degree of pre-stress [1]. Using a new Force Distribution Analysis of forces obtained from Molecular Dynamics simulations [2], we identified particularly tensed disulfides, with inter-cysteine forces of 143.34 pN for Cys130-Cys159 in CD4 and 165.47 pN for Cys27-Cys37 in the von Willebrand factor C1 (vWFC1) domain. Remarkably, the order of magnitude of these internal forces is coinciding with those required to unfold or activate proteins, and thus likely to play an important role in the protein's integrity. The pre-stressed disulfide bonds link adjacent strands in the same antiparallel β-sheet, and have been previously classified as ‘allosteric disulfide bonds’ due to their unusual and unfavourable dihedral configuration [3]. We calculate reduction rates of the two disulfide bonds to increase due to the intrinsic tension by a factor of two to three as compared to the other comparably relaxed disulfide bonds in CD4 and vWFC1. This trend is preserved in a survey over all disulfide bonds in protein structures currently deposited in the Protein Data Bank, with disulfide bonds linking two adjacent strands in a β-sheet featuring a significantly larger sulphur-sulphur bond length on average. The decreased thermodynamic and kinetic stability of pre-stressed disulfide bonds as identified in our proteome-wide survey is likely to have functional implications, in particular in the light of mechano-chemical disulfide bond shuffling of von Willebrand factor an other highly disulfide-linked proteins.