@article {2018|2136, title = {Forcing the reversibility of a mechanochemical reaction}, journal = {Nat Commun}, volume = {9}, year = {2018}, month = {08}, pages = {3155}, abstract = {

Mechanical force modifies the free-energy surface of chemical reactions, often enabling thermodynamically unfavoured reaction pathways. Most of our molecular understanding of force-induced reactivity is restricted to the irreversible homolytic scission of covalent bonds and ring-opening in polymer mechanophores. Whether mechanical force can by-pass thermodynamically locked reactivity in heterolytic bimolecular reactions and how this impacts the reaction reversibility remains poorly understood. Using single-molecule force-clamp spectroscopy, here we show that mechanical force promotes the thermodynamically disfavored SN2 cleavage of an individual protein disulfide bond by poor nucleophilic organic thiols. Upon force removal, the transition from the resulting high-energy unstable mixed disulfide product back to the initial, low-energy disulfide bond reactant becomes suddenly spontaneous, rendering the reaction fully reversible. By rationally varying the nucleophilicity of a series of small thiols, we demonstrate how force-regulated chemical kinetics can be finely coupled with thermodynamics to predict and modulate the reversibility of bimolecular mechanochemical reactions.

}, doi = {10.1038/s41467-018-05115-6}, author = {Beedle, Amy E M and Mora, Marc and Davis, Colin T and Snijders, Ambrosius P and Guillaume Stirnemann and Garcia-Manyes, Sergi} } @article {2017|2026, title = {Tailoring protein nanomechanics with chemical reactivity}, journal = {Nat Commun}, volume = {8}, year = {2017}, month = {Jun}, pages = {15658}, abstract = {

The nanomechanical properties of elastomeric proteins determine the elasticity of a variety of tissues. A widespread natural tactic to regulate protein extensibility lies in the presence of covalent disulfide bonds, which significantly enhance protein stiffness. The prevalent in vivo strategy to form disulfide bonds requires the presence of dedicated enzymes. Here we propose an alternative chemical route to promote non-enzymatic oxidative protein folding via disulfide isomerization based on naturally occurring small molecules. Using single-molecule force-clamp spectroscopy, supported by DFT calculations and mass spectrometry measurements, we demonstrate that subtle changes in the chemical structure of a transient mixed-disulfide intermediate adduct between a protein cysteine and an attacking low molecular-weight thiol have a dramatic effect on the protein\&$\#$39;s mechanical stability. This approach provides a general tool to rationalize the dynamics of S-thiolation and its role in modulating protein nanomechanics, offering molecular insights on how chemical reactivity regulates protein elasticity.

}, doi = {10.1038/ncomms15658}, author = {Beedle, Amy E M and Mora, Marc and Lynham, Steven and Guillaume Stirnemann and Garcia-Manyes, Sergi} } @article {2015|1729, title = {The mechanochemistry of copper reports on the directionality of unfolding in model cupredoxin proteins.}, journal = {Nature Comm.}, volume = {6}, year = {2015}, pages = {7894}, abstract = {

Understanding the directionality and sequence of protein unfolding is crucial to elucidate the underlying folding free energy landscape. An extra layer of complexity is added in metalloproteins, where a metal cofactor participates in the correct, functional fold of the protein. However, the precise mechanisms by which organometallic interactions are dynamically broken and reformed on (un)folding are largely unknown. Here we use single molecule force spectroscopy AFM combined with protein engineering and MD simulations to study the individual unfolding pathways of the blue-copper proteins azurin and plastocyanin. Using the nanomechanical properties of the native copper centre as a structurally embedded molecular reporter, we demonstrate that both proteins unfold via two independent, competing pathways. Our results provide experimental evidence of a novel kinetic partitioning scenario whereby the protein can stochastically unfold through two distinct main transition states placed at the N and C termini that dictate the direction in which unfolding occurs.

}, isbn = {doi:10.1038/ncomms8894}, issn = {2041-1723}, doi = {10.1038/ncomms8894}, url = {http://www.nature.com/ncomms/2015/150803/ncomms8894/abs/ncomms8894.html}, author = {Beedle, Amy E M and Lezamiz, Ainhoa and Guillaume Stirnemann and Garcia-Manyes, Sergi} }