Chymotrypsin catalyses hydrolysis reactions. Like other enzymes, chymotrypsin has a natural tendancy to degrade at air–water surfaces, losing its structure and catalytic activity. Rotello and colleagues say the enzyme can be stabilised by surrounding it with monolayer-protected gold nanoparticles (MPNs). MPNs are spherical nano-structures in which gold nanoparticles are surrounded by a negatively-charged shell of tetra(ethylene glycol) carboxylate ligands.
According to Rotello, MPNs are roughly the same size as chymotrypsin (about six nanometres in diameter), and bind electrostatically to the enzyme in water. This stabilises the enzyme by restricting its ability to unfold at the air-water surface.
‘The key finding is that we can stabilise proteins under conditions that would normally reduce or eliminate their activity,’ explained Rotello. ‘At the moment, each protein is a special case that requires a new answer. Once we understand the process, it should be much easier to tailor particles to stabilise specific proteins.’
Rotello said the findings are significant for technologies that use enzymes to catalyse reactions at air–water surfaces.
Qun Huo, an expert in nanomaterials at the Universtiy of Central Florida, US, noted the potential applications of Rotello’s research. ‘This is a very elegant approach of using nanotechnology to solve one of the long-standing problems in the biotechnology area,’ said Huo. ‘This work from Rotello’s group will have a significant impact in many areas such as biosensor development, where the stablilisation of enzymes and proteins has been one of the key limiting factors in the field.’