Viral nanoreactor captures single molecules

Researchers in the Netherlands have created a biochemical nanoreactor by cracking open a virus, removing its contents then reassembling the virus’s protein coat around a single molecule of enzyme. 

Marta Comellas-Aragon?s and colleagues from Radboud University Nijmegen, Eindhoven University of Technology and Wageningen University, split open the protein coat of the cowpea chlorotic mottle virus, which can be made to reversibly fall apart or reassemble depending on the pH. They then reassembled the coat proteins in the presence of the enzyme horseradish peroxidise, trapping a single molecule of the enzyme inside each virus. 

The researchers were able to demonstrate that the enzyme remained active within the cage, and that substrate molecules could enter the viral shell and products diffuse out. By changing the pH, the team were also able to alter how easily small molecules passed in and out. 

Single molecules of enzyme can behave very differently to bulk enzyme systems, but they often have to be tethered to a surface physically or chemically to be studied - potentially altering their activity. 

Hans Engelkamp, a member of the research team, believes that the nanoreactor could provide a way of studying a single enzyme molecule without having to pin it down. The enclosed environment within the virus also more closely mimics the small spaces within a cell, Engelkamp added.

Commenting on the work, Raphael Levy, a bionanotechnology researcher at the University of Liverpool, UK, told Chemistry World: ’Enclosing a single molecule in a box seems to be a rather extraordinary challenge. That is, however, what Marta Comellas-Aragon?s and colleagues have achieved using a virus as a box to enclose an enzyme.’

Levy added that the approach could be used to study artificial anzymatic cascades, with the viral cage isolating the enzyme until it is ready to be dropped into the right place.

Adrian Mulholland, an enzymologist at the University of Bristol, UK, said, ’Single-molecule enzyme assays are changing how biochemical reactions are studied. The effects of averaging are removed, allowing direct study of molecular fluctuations and distributions; and short-lived reaction intermediates can be identified. The viral encapsulation approach developed here looks a promising method for single molecule enzyme assays.’ 

Simon Hadlington