Plant compounds in muscadine grapes block coronavirus replication

Chemical compounds that plants use to protect themselves may also help to protect people from COVID-19 infection, according to a new study from at North Carolina State University.

Plant compounds found in muscadine grapes, dark chocolate, and green tea can bind to and inhibit the coronavirus’ main protease (Mpro), which plays a key role in viral gene expression and replication.

Study co-author and plant biologist Professor De-Yu Xie explained that proteases are important to the health and viability of cells and viruses. For example, cells cannot perform many important functions like replication if proteases are inhibited. 

“One of our lab’s focuses is to find nutraceuticals in food or medicinal plants that inhibit either how a virus attaches to human cells or the propagation of a virus in human cells,” said Professor Xie.

The researchers set out to investigate how Mpro in the SARS-CoV-2 virus would react when it encountered a number of different plant chemical compounds that are known for having powerful antioxidant properties. 

Using computer simulations, the experts demonstrated that chemical compounds from green tea, two varieties of muscadine grapes, cacao powder and dark chocolate were able to bind to different portions of Mpro.

“Mpro in SARS-CoV-2 is required for the virus to replicate and assemble itself. If we can inhibit or deactivate this protease, the virus will die,” said Professor Xie. “Mpro has a portion that is like a ‘pocket’ that was ‘filled’ by the chemical compounds. When this pocket was filled, the protease lost its important function.”

Lab experiments conducted in Professor Xie’s lab by PhD student Yue Zhu confirmed the results of the computer simulations. The chemical compounds in green tea and muscadine grapes were very successful at blocking the function of Mpro. In addition, plant compounds in cacao powder and dark chocolate reduced Mpro activity by about half.

“Green tea has five tested chemical compounds that bind to different sites in the pocket on Mpro, essentially overwhelming it to inhibit its function,” said Professor Xie. “Muscadine grapes contain these inhibitory chemicals in their skins and seeds. Plants use these compounds to protect themselves, so it is not surprising that plant leaves and skins contain these beneficial compounds.”

The study is published in the journal Frontiers in Plant Science.

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By Chrissy Sexton, Earth.com Staff Writer