US chemists have used a virus capsule to package and release molecules, which could lead to targeted delivery of therapeutic compounds.

Stefan Franzen and his colleagues at North Carolina State University in Raleigh used the red clover necrotic mosaic virus as a vehicle for dye molecules that can be loaded and unloaded on demand.

Red clover necrotic mosaic virus is a plant virus with a protein shell, or capsid, of multiple subunits that self-assemble to form a cage. Franzen explained that, 'these protein cages offer a rigid structure with an interior cavity that can function as an ideal container for cargo encapsulation'.

To explore its versatility for nano-packaging and delivery, Franzen first worked on capturing dye molecules into the capsid. As divalent ions are integral to the virus structure, Ca²⁺ and Mg²⁺ depletion in the solution induces significant conformational changes.  This leads to surface pores forming, allowing dye molecules to infuse into the interior cavity. Restoring the ion balance closes the pores, trapping the dye inside the virus.  When Franzen lowered the ion concentration, the pores reopened and the dye molecules were released.

Franzen's final aim is to use the capsids for intracellular drug delivery - the next stage is to study their ability to package and deliver cargo into a target cell, he explained.    The idea is that loaded viruses should be triggered to open their surface pores and release their package inside a cell where the divalent ion concentrations are low. This concept is 'advantageous because the virus capsid will be able to act as container to protect a cargo until it reaches the targeted cell to be released', explained Franzen.

Michael Spencelayh