title: Continuous observation of the stochastic motion of an individual small-molecule walker.
abstract: Motion--whether it the ability to change shape, rotate or translate--is an important potential asset for functional nanostructures. For translational motion, a variety of DNA-based and small-molecule walkers have been created, but observing the translational motion of individual molecules in real time remains a significant challenge. Here, we show that the movement of a small-molecule walker along a five-foothold track can be monitored continuously within a protein nanoreactor. The walker is an organoarsenic(III) molecule with exchangeable thiol ligands, and the track a line of cysteine residues 6 Å apart within an α-haemolysin protein pore that acts as the nanoreactor. Changes in the flow of ionic current through the pore reflect the individual steps of a single walker, which require the making and breaking of As-S bonds, and occur in aqueous solution at neutral pH and room temperature. The walker moves considerably faster (∼0.7 s per step) than previous walkers based on covalent chemistry and is weakly processive (6 ± 1 steps per outing). It shows weak net directional movement, which can be described by a thermodynamic sink arising from the different environments of the cysteines that constitute the track.
authors.affiliation: Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK.
authors.forename: Gökçe Su
authors.initials: GS
authors.lastname: Pulcu
authors.affiliation: Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK.
authors.forename: Ellina
authors.initials: E
authors.lastname: Mikhailova
authors.affiliation: Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK.
authors.forename: Lai-Sheung
authors.initials: LS
authors.lastname: Choi
authors.affiliation: Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK.
authors.forename: Hagan
authors.initials: H
authors.lastname: Bayley
mesh_terms: D001151:Arsenic / Q000737:chemistry*; D001427:Bacterial Toxins / Q000737:chemistry*; D003198:Computer Simulation; D003545:Cysteine / Q000737:chemistry*; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000648:ultrastructure; D008422:Materials Testing; D008956:Models, Chemical; D015233:Models, Statistical; D009038:Motion; D058608:Nanopores / Q000648:ultrastructure; D013269:Stochastic Processes
chemical_list: D001427:Bacterial Toxins; D006460:Hemolysin Proteins; C021091:staphylococcal alpha-toxin; D003545:Cysteine; D001151:Arsenic