Observing Confined Local Oxygen‐induced Reversible Thiol/Disulfide Cycle with a Protein Nanopore

Abstract Disulfide bonds play an important role in thiol‐based redox regulation. However, owing to the lack of analytical tools, little is known about how local O 2 mediates the reversible thiol/disulfide cycle under protein confinement. In this study, a protein‐nanopore inside a glove box is used to control local O 2 for single‐molecule reaction, as well as a single‐molecule sensor for real‐time monitoring of the reversible thiol/disulfide cycle. The results demonstrate that the local O 2 molecules in protein nanopores could facilitate the redox cycle of disulfide formation and cleavage by promoting a higher fraction of effective reactant collisions owing to nanoconfinement. Further kinetic calculations indicate that the negatively charged residues near reactive sites facilitate proton‐involved oxygen‐induced disulfide cleavage under protein confinement. The unexpectedly strong oxidation ability of confined local O 2 may play an essential role in cellular redox signaling and enzyme reactions.