# The catalytic tetrad of Aedes aegypti argonaute 2 is critical for the antiviral activity of the exogenous siRNA pathway

## TL;DR

Aedes aegypti mosquitoes use a protein called Argonaute 2 to fight viruses, and a specific group of amino acids is essential for this defense.

## Contribution

The study confirms the role of a catalytic tetrad in Aedes aegypti Ago2 for antiviral activity via the exo-siRNA pathway.

## Key findings

- The catalytic tetrad (D740, E780, D812, H950) in Ae. aegypti Ago2 is essential for antiviral activity.
- Absence of the tetrad leads to accumulation of siRNA duplexes and loss of pathway function.
- The tetrad is necessary for degradation of siRNA passenger strands.

## Abstract

Viruses transmitted by biting arthropods, arboviruses, pose a significant global health and economic threat. Climate change is exacerbating this issue by expanding the range of disease-carrying vectors. Effective control of arbovirus transmission often relies on targeting the vectors, making it crucial to understand the interactions between the virus and its vector. The exogenous siRNA (exo-siRNA) pathway is a key antiviral defense mechanism in mosquitoes such as Aedes aegypti. Argonaute 2 (Ago2) is a central protein in this pathway, responsible for antiviral activity. While the PIWI domain of Ago proteins is known to mediate slicing activity, not all Ago proteins possess this slicing function. To understand the antiviral mechanism of Ago2 in Ae. aegypti, we aimed to confirm the presence of the catalytic tetrad, a group of amino acids known to be crucial for slicing activity. Here, we confirmed the tetrad (D740, E780, D812, and H950) in Ae. aegypti Ago2 and demonstrated its essential role in antiviral and siRNA pathway activity. Our findings show that the catalytic tetrad is necessary for the degradation of siRNA passenger strands. When the tetrad is absent, siRNA duplexes accumulate, leading to a loss of siRNA pathway function. This underscores the critical role of the tetrad in the antiviral defense mechanism of Ae. aegypti.