# Molecular structure of the ESCRT-III-based archaeal CdvAB cell division machinery

## TL;DR

This study reveals the molecular structure of the archaeal CdvAB cell division machinery, showing how it uses ESCRT-III-like proteins to drive cytokinesis.

## Contribution

The study provides the first detailed molecular architecture of archaeal Cdv proteins and their role in membrane remodeling during cell division.

## Key findings

- CdvA forms antiparallel helical filaments with a PRC-domain/coiled-coil fold.
- CdvB proteins adopt the canonical ESCRT-III fold and transition to an active state on membranes.
- N-terminal helices in CdvB mediate membrane binding and are essential for liposome recruitment.

## Abstract

Membrane remodeling by ESCRT-III proteins is a fundamental and conserved process across the tree of life. The archaeal ESCRT-III-based cell division system (Cdv) drives cytokinesis in many archaeal groups, yet the molecular architecture of its components remained unknown, making it difficult to decipher the molecular mechanisms employed for cell division and cytokinesis in these organisms. We present structures of the Cdv machinery in Sulfolobus organisms that have been used previously to study the cell division process. We show that CdvA forms unexpected antiparallel helical filaments, while the ESCRT-III homologues retain the canonical fold they share with eukaryotic proteins. We demonstrate that N-terminal helices mediate membrane binding and that membrane contact, rather than polymerization alone, likely triggers activation of Cdv ESCRT-IIIs.

Most prokaryotes divide using filaments of the tubulin-like FtsZ protein, while some archaea employ instead ESCRT-III-like proteins and their filaments for cell division and cytokinesis. The alternative archaeal system comprises Cdv proteins and is thought to bear some resemblance to ESCRT-III-based membrane remodeling in other domains of life, including eukaryotes, especially during abscission. Here, we present biochemical, crystallographic, and cryo-EM studies of the Sulfolobus Cdv machinery. CdvA, an early non-ESCRT component, adopts a PRC‐domain/coiled-coil fold and polymerizes into long double-stranded helical filaments, mainly via hydrophobic interfaces. Monomeric CdvB adopts the canonical ESCRT-III fold in both a closed and a distinct “semiopen” conformation. Soluble CdvB2 filaments are composed of subunits in the closed state, appearing to transition to the open, active state only when polymerized on membranes. Short N-terminal amphipathic helices in all CdvB paralogues, B, B1, and B2, mediate membrane binding and are required for liposome recruitment in vitro. We provide a molecular overview of archaeal ESCRT-III-based cytokinesis machinery, the definitive demonstration that CdvB proteins are bona fide ESCRT-III homologues, and reveal the molecular basis for membrane engagement. Thus, we illuminate conserved principles of ESCRT-mediated membrane remodeling and extend them to an anciently diverged archaeal lineage.