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

Florian Fäßler,Florian K M Schur,Georgi Dimchev,Victor-Valentin Hodirnau,William Wan

doi:10.1038/s41467-020-20286-x

Florian Fäßler, Florian K M Schur + Show 3 more

Open Access

https://doi.org/10.1038/s41467-020-20286-x

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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.

Highlights

The actin-related protein (Arp)2/3 complex nucleates branched actin filament networks pivotal for cell migration, endocytosis and pathogen infection
Due to the large number of actin filament Arp2/3 complex branch junctions within lamellipodia, we considered them the optimal target to determine the structure of branch junctions in their native environment at the highest possible resolution, and to provide the outstanding answers to the important aforementioned open points on branch junction formation and stability
We report, using cryo-electron tomography (ET) and subtomogram averaging (STA) on lamellipodia of fibroblast cells, a 9 Å structure of the actin filament Arp2/3 complex branch junction. This allows us to obtain an accurate model of the active Arp2/3 complex in the branch junction, which reveals a new set of interactions within the complex and with the mother filament, different to previous models

Summary

Introduction

The actin-related protein (Arp)2/3 complex nucleates branched actin filament networks pivotal for cell migration, endocytosis and pathogen infection. Due to the low resolutions (~25 Å) of the previously determined branch junction model, the currently suggested molecular contacts of the active Arp2/3 complex in the branch junction and the associated changes in the mother filament remain ambiguous.

Results

Conclusion