Mechanoradicals in tensed tendon collagen as a source of oxidative stress

Christopher Zapp,Reinhard Kappl,Frauke Gräter,Thomas Prisner,Benedikt Rennekamp,Davide Mercadante,David M Hudson,Uladzimir Barayeu,Tobias P Dick,Markus Kurth,Csaba Daday,Marina Bennati,Agnieszka Obarska-Kosinska,Vasyl Denysenkov

doi:10.1038/s41467-020-15567-4

Abstract

As established nearly a century ago, mechanoradicals originate from homolytic bond scission in polymers. The existence, nature and biological relevance of mechanoradicals in proteins, instead, are unknown. We here show that mechanical stress on collagen produces radicals and subsequently reactive oxygen species, essential biological signaling molecules. Electron-paramagnetic resonance (EPR) spectroscopy of stretched rat tail tendon, atomistic molecular dynamics simulations and quantum-chemical calculations show that the radicals form by bond scission in the direct vicinity of crosslinks in collagen. Radicals migrate to adjacent clusters of aromatic residues and stabilize on oxidized tyrosyl radicals, giving rise to a distinct EPR spectrum consistent with a stable dihydroxyphenylalanine (DOPA) radical. The protein mechanoradicals, as a yet undiscovered source of oxidative stress, finally convert into hydrogen peroxide. Our study suggests collagen I to have evolved as a radical sponge against mechano-oxidative damage and proposes a mechanism for exercise-induced oxidative stress and redox-mediated pathophysiological processes.

Highlights

As established nearly a century ago, mechanoradicals originate from homolytic bond scission in polymers
Our joint simulations and experiments show that radicals from primary irreversible bond scission in these crosslink regions migrate to dihydroxyphenylalanine (DOPA), which form by posttranslational modifications from phenylalanine and tyrosine residues
We showed with light absorbance that the DOPA radicals were converted into hydrogen peroxide in the presence of water, putting forward a role of collagen in the conversion of mechanical into oxidative stress in connective tissues

Summary

Introduction

As established nearly a century ago, mechanoradicals originate from homolytic bond scission in polymers. Electronparamagnetic resonance (EPR) spectroscopy of stretched rat tail tendon, atomistic molecular dynamics simulations and quantum-chemical calculations show that the radicals form by bond scission in the direct vicinity of crosslinks in collagen. Our joint simulations and experiments show that radicals from primary irreversible bond scission in these crosslink regions migrate to dihydroxyphenylalanine (DOPA), which form by posttranslational modifications from phenylalanine and tyrosine residues. These aromatic residues cluster in evolutionarily highly conserved regions. We showed with light absorbance that the DOPA radicals were converted into hydrogen peroxide in the presence of water, putting forward a role of collagen in the conversion of mechanical into oxidative stress in connective tissues

Methods

Results

Conclusion