Recent studies have shown that the diffusivity of enzymes increases in a substrate-dependent manner during catalysis1,2. Although this observation has been reported and characterized for several different systems3–10, the precise origin of this phenomenon is unknown. Calorimetric methods are often used to determine enthalpies from enzyme-catalysed reactions and can therefore provide important insight into their reaction mechanisms11,12. The ensemble averages involved in traditional bulk calorimetry cannot probe the transient effects that the energy exchanged in a reaction may have on the catalyst. Here we obtain single-molecule fluorescence correlation spectroscopy data and analyse them within the framework of a stochastic theory to demonstrate a mechanistic link between the enhanced diffusion of a single enzyme molecule and the heat released in the reaction. We propose that the heat released during catalysis generates an asymmetric pressure wave that results in a differential stress at the protein–solvent interface that transiently displaces the centre-of-mass of the enzyme (chemoacoustic effect). This novel perspective on how enzymes respond to the energy released during catalysis suggests a possible effect of the heat of reaction on the structural integrity and internal degrees of freedom of the enzyme.

Single-molecule measurements combined with a novel mathematical strategy were applied to accurately characterize how bimolecular interactions respond to mechanical force, especially when protein purification is not possible. Specifically, we studied the effect of force on Thy-1/αvβ3 integrin interaction, a mediator of neuron-astrocyte communication.

BiP (Immunoglobulin Binding Protein) is a member of the Hsp70 chaperones that participates in protein folding in the endoplasmic reticulum. The function of BiP relies on cycles of ATP hydrolysis driving the binding and release of its substrate proteins. It still remains unknown how BiP affects the protein folding pathway and there has been no direct demonstration showing which folding state of the substrate protein is bound by BiP, as previous work has used only peptides. Here, we employ optical tweezers for single molecule force spectroscopy experiments to investigate how BiP affects the folding mechanism of a complete protein and how this effect depends on nucleotides. Using the protein MJ0366 as the substrate for BiP, we performed pulling and relaxing cycles at constant velocity to unfold and refold the substrate. In the absence of BiP, MJ0366 unfolded and refolded in every cycle. However, when BiP was added, the frequency of folding events of MJ0366 significantly decreased, and the loss of folding always occurred after a successful unfolding event. This process was dependent on ATP and ADP, since when either ATP was decreased or ADP was added, the duration of periods without folding events increased. Our results show that the affinity of BiP for the substrate protein increased in these conditions, which correlates with previous studies in bulk. Therefore, we conclude that BiP binds to the unfolded state of MJ0366 and prevents its refolding, and that this effect is dependent on both the type and concentration of nucleotides.