# Cryo-electron tomography structure of Arp2/3 complex in cells reveals new insights into the branch junction

## TL;DR

This study uses cryo-electron tomography to reveal the structure of the Arp2/3 complex in cells, providing new insights into how it forms branched actin networks.

## Contribution

The paper presents the first 9.0 Å resolution structure of the Arp2/3 complex branch junction in cells, revealing new interactions and the role of the ArpC3 subunit.

## Key findings

- A new model of the Arp2/3 complex interacting with actin filaments was generated.
- Previously unknown interactions between the Arp2/3 complex and the mother filament were identified.
- The ArpC3 subunit plays a central role in stabilizing the active Arp2/3 complex conformation.

## Abstract

The actin-related protein (Arp)2/3 complex nucleates branched actin filament networks pivotal for cell migration, endocytosis and pathogen infection. Its activation is tightly regulated and involves complex structural rearrangements and actin filament binding, which are yet to be understood. Here, we report a 9.0 Å resolution structure of the actin filament Arp2/3 complex branch junction in cells using cryo-electron tomography and subtomogram averaging. This allows us to generate an accurate model of the active Arp2/3 complex in the branch junction and its interaction with actin filaments. Notably, our model reveals a previously undescribed set of interactions of the Arp2/3 complex with the mother filament, significantly different to the previous branch junction model. Our structure also indicates a central role for the ArpC3 subunit in stabilizing the active conformation.

The actin-related protein (Arp)2/3 complex nucleates branched actin filament networks pivotal for cell migration, endocytosis and pathogen infection. Here, authors report a 9.0 Å resolution structure of the actin filament Arp2/3 complex branch junction in cells using cryo-electron tomography and subtomogram averaging.