Controlling nanocapsules with biovalves

 

 

At a neutral pH, the biovalve opens, chemical compounds can enter the capsule, and are enzymatically converted. As soon as the pH in the environment changes and becomes slightly sour, the biovalve closes (Image: Departement of Chemistry, University of Basel).

The group run by Professor Cornelia Palivan and Professor Wolfgang Meier from the Department of Chemistry at the University of Basel has recently produced synthetic nanocapsules that allow enzymatic reactions to be controlled externally. To achieve this, the team integrated biovalves into the capsule membrane that can be switched on and off once a certain pH value is reached. This creates the conditions required to activate and deactivate a controlled enzymatic reaction inside the capsule. This innovative technology, used for the first time, has great potential for medical applications, catalysis, and analytical chemistry.

Cells of higher organisms are divided into compartments with different functions (mitochondria, peroxisome, nucleus, etc). These compartments are separated from the cytoplasm by membranes. Proteins integrated into these membranes control the active and passive passage of chemical compounds in and out of the different compartments. Often, passage is triggered by external stimuli such as pH, membrane potential, specific chemical substances, or light.

Nature as a role model
Researchers led by Professor Cornelia Palivan and Professor Wolfgang Meier from the SNI and Department of Chemistry at the University of Basel have taken nature as their role model in developing controllable compartments. First, they created robust, synthetic compartments using synthetic membranes that enclose natural enzymes. They then combined modified channel proteins with a peptide that is sensitive to pH changes in the environment, and integrated these into the polymer membranes. At a neutral pH, the biovalve opens, chemical compounds can enter the capsule, and are enzymatically converted. Afterwards, the products of the enzymatic reaction can leave the capsule again. As soon as the pH in the environment changes and becomes slightly sour, the biovalve closes. As the passage of the essential substrates is blocked, no enzymatic reaction takes place in the compartment.

Basis for numerous applications
With this innovative strategy, scientists from Basel have developed synthetic nanocapsules with reversible “gates” through which enzymatic activity is triggered by external stimuli. They have combined the advantages of the robust and variable polymer capsules with those of genetically modified natural channel proteins by attaching a stimuli-responsive peptide to the channel protein. “In comparison to other strategies, our approach is technically simple,” says Palivan. The capsules are formed by self-assembly. As the enclosed and well-protected enzymes in the capsules can be varied, and the properties of the polymer membranes can be changed according to specific needs, this strategy has great potential for applications in medicine, catalysis and analytic chemistry.