# Insect I‐Type Lysozymes Function as Antiviral Proteases by Forming Biomolecular Condensates

## TL;DR

Insects use a type of lysozyme to fight viruses by cutting viral proteins and forming droplet-like structures that boost this antiviral activity.

## Contribution

Discovers that insect i-type lysozymes act as antiviral proteases by cleaving viral proteins and forming biomolecular condensates.

## Key findings

- Lyz-I1 cleaves the viral protein Pns9 at Lys180, disrupting viroplasm assembly and viral replication.
- Lyz-I1 forms biomolecular condensates via liquid–liquid phase separation, enhancing antiviral proteolytic efficiency.
- Exogenous Lyz-I1 reduces viral titer and disease symptoms in infected rice plants while inducing plant immune defense.

## Abstract

Lysozymes are well‐known for their ability to cleave bacterial peptidoglycan, but their potential to hydrolyze viral components as a form of antiviral defense remains poorly understood. This study demonstrates that insect i‐type lysozymes (Lyz‐I1), regulated by the Toll signaling pathway, function as proteases that directly cleave viral proteins. Structural and functional analyses reveal that the catalytic dyad Glu34/Asp50 in leafhopper Lyz‐I1, while retaining its essential role in bacterial peptidoglycan hydrolysis, also mediates specific binding to Lys180 on the viroplasm protein Pns9 of rice gall dwarf virus (RGDV). This interaction catalyzes the cleavage of the adjacent peptide bond of Lys180, leading to Pns9 degradation, which disrupts viroplasm assembly and inhibits viral replication. Notably, this proteolytic antiviral mechanism of Lyz‐I1 shows evolutionary conservation across major rice reoviruses and their respective leafhopper or planthopper vectors. Additionally, leafhopper Lyz‐I1 undergoes liquid–liquid phase separation, forming biomolecular condensates that concentrate Pns9 and enhance proteolytic efficiency. Critically, exogenous application of Lyz‐I1 not only effectively reduces viral titer and disease symptoms in RGDV‐infected rice plants but also induces plant immune defense. Consequently, this work provides the evidence that lysozymes can function as specific antiviral proteases, establishing a foundation for innovative control strategies against viral diseases.

Upon rice viral infection, the insect vector activates the Toll–MyD88–Dorsal signaling cascade, inducing i‐type lysozyme (Lyz‐I1) expression. Lyz‐I1 functions as an antiviral protease through its conserved catalytic dyad Glu/Asp (E/D), mediating cleavage of viral proteins at specific Lys (K) residues. This site‐specific proteolysis disrupts essential viral protein functions, thereby inhibiting viral replication.