# CLDN3 inhibits rotavirus attachment by targeting residue 74 of VP7

## TL;DR

This study shows how the protein CLDN3 blocks rotavirus from attaching to cells by interacting with a specific part of the virus's VP7 protein.

## Contribution

The study reveals a novel antiviral mechanism where CLDN3 inhibits rotavirus attachment via interaction with VP7 residue E74.

## Key findings

- CLDN3 mislocalization and reduced protein levels during rotavirus infection promote viral binding and entry.
- The CLDN3 EC1 loop interacts with VP7's N-terminal domain, with E74 being critical for this interaction.
- The E74K mutation in VP7 disrupts CLDN3 binding and increases viral pathogenicity in vivo.

## Abstract

Rotavirus (RV) VP8* peptide-induced CLDN3 mislocalization supports the hypothesis that CLDN3 negatively regulates viral binding, while the molecular basis of this inhibitory function remains unresolved. To counteract the CLDN3 defense strategies, RV infection indeed disrupts its localization to the plasma membrane. We also found that RV infection could reduce its protein levels in both in vitro and animal models. Knockdown or knockout of CLDN3 effectively promotes RV binding and entry. Further, we found that CLDN3 EC1 loop could interact with the N-terminal domain of VP7 and structural studies reveal a conserved glutamic acid at position 74 (E74) in VP7 as critical for the CLDN3-VP7 interaction. Mechanistically, VP7 is involved in viral attachment. Binding of the CLDN3 EC1 loop to VP7 reduces viral adsorption, whereas the E74K mutation disrupts the CLDN3-VP7 interaction and consequently enhances viral attachment. More importantly, a single E74K mutation enhances viral pathogenicity in vivo, confirming this interaction’s biological significance. Our results demonstrate for the first time that the tight junction protein CLDN3 acts as a decoy receptor that specifically counters the VP7-mediated viral attachment. This highlights the antiviral mechanisms utilized by CLDN3.

Rotavirus (RV) is a major global pathogen, and understanding the intricate battle between the virus and host defenses is critical. While it is known that RV infection disrupts tight junction proteins like claudins (CLDNs) to facilitate its entry, the specific protective mechanisms of these proteins remain unknown. Our study demonstrated that VP7 glycoprotein is involved in RV adsorption, and CLDN3 as a decoy receptor that directly counters its attachment function. VP7 E74 residue is a key site responsible for association with CLDN3 EC1 loop. The conservation and functional essentiality of the VP7 E74 residue, validated by its profound impact on viral binding and pathogenicity, underscore that VP7 is also an important virulence factor. We elucidate a novel mechanism by which CLDN3 inhibits rotavirus adsorption. This work not only reveals a new front in the host-virus arms race but also identifies a potential target for the development of broad-spectrum antiviral strategies.