# The Interaction Between Orientin and the Spike of SARS-CoV-2: An In Silico and Experimental Approach

## TL;DR

This study explores how Orientin, a flavonoid, interacts with the SARS-CoV-2 Spike protein and may help inhibit viral replication.

## Contribution

The study is the first to investigate Orientin's interaction with the SARS-CoV-2 Spike protein using both computational and experimental methods.

## Key findings

- Orientin binds to key residues in the Spike protein's receptor-binding domain.
- Orientin moderately inhibits SARS-CoV-2 replication in Vero cells without cytotoxicity.
- Fluorescence data suggest direct interaction between Orientin and the Spike protein.

## Abstract

SARS-CoV-2, the causative agent of COVID-19, has led to over seven million deaths worldwide prior to May 2025. Despite widespread vaccination programs, COVID-19 remains a persistent global health challenge, underscoring the urgent need for new therapeutic approaches. Orientin is a flavonoid with reported antiviral activity, though its potential against SARS-CoV-2 remains poorly explored. This study aimed to investigate whether Orientin interacts with the viral Spike protein and impacts viral replication. Molecular docking simulations using DockThor were employed to predict the binding affinity between Orientin and the receptor-binding domain (RBD) of the Spike protein. Fluorescence spectroscopy assays were performed to assess direct interactions between Orientin and the trimeric form of the Spike protein. Additionally, cytotoxicity and viral replication assays were carried out in Vero cells to evaluate Orientin’s antiviral effects. Docking results indicated that Orientin likely binds to key RBD residues involved in ACE2 receptor recognition. Spectroscopic analyses showed a decrease in intrinsic tryptophan fluorescence, suggesting direct interaction. Orientin demonstrated no cytotoxicity in Vero cells and exhibited moderate inhibition of viral replication. These findings suggest that Orientin interacts with critical regions of the Spike protein and may act as a moderate in vitro inhibitor of SARS-CoV-2, warranting further investigation into its therapeutic potential.