# Structural insights into SetA-mediated Rab1 glucosylation and PI3P-guided localization during early Legionella infection

## TL;DR

This paper reveals how the bacterial protein SetA modifies a host protein (Rab1) and targets specific membranes during early stages of Legionella infection, helping the bacteria create a safe environment to replicate.

## Contribution

The study provides new structural and mechanistic insights into how SetA simultaneously glucosylates Rab1 and localizes to PI3P-rich membranes during Legionella infection.

## Key findings

- SetA selectively modifies GDP-bound Rab1 and targets PI3P-enriched membranes during LCV maturation.
- Structural analysis shows how SetA integrates Rab1 modification with membrane localization to disrupt Golgi and ER dynamics.
- The dual mechanisms of SetA provide a spatiotemporal framework for understanding Legionella's early infection strategy.

## Abstract

Legionella pneumophila remodels host membrane trafficking to establish a replication-permissive niche, yet the molecular basis of this process is not fully understood. Here, we elucidate the structural basis by which the effector SetA couples Rab1 glucosylation with PI3P-guided membrane localization during early Legionella-containing vacuole (LCV) maturation. By determining multiple structures of SetA and combining with biochemical and cellular analyses, we reveal how SetA selectively modifies GDP-bound Rab1 and targets PI3P-enriched membranes, thereby influencing early membrane remodeling events associated with LCV development. These findings uncover an integrated mechanism through which a single bacterial effector orchestrates both spatial positioning and enzymatic activity to modulate host organelle dynamics, providing an insight into early stages of Legionella infection.

The bacterial pathogen Legionella pneumophila secretes effector proteins that remodel host endomembranes to establish a replication-permissive niche known as the Legionella-containing vacuole (LCV). Among these, SetA disrupts vesicle trafficking by glucosylating the small GTPase Rab1, essential for ER-to-Golgi transport. Here, we report comprehensive structural and mechanistic insights into SetA-mediated Rab1 glucosylation and its PI3P-dependent membrane targeting. Crystal structures of its N-terminal glycosyltransferase and C-terminal lipid-binding domains, captured in multiple ligand-bound states, reveal how SetA specifically recognizes GDP-bound Rab1 and the head group of phosphatidylinositol 3-phosphate (PI3P), which is enriched on early LCV membranes. SAXS-based full-length modeling, biochemical assays, and cellular imaging analyses demonstrate that SetA integrates Rab1 modification with membrane localization, thereby perturbing Golgi integrity and ER morphology. Together, these findings define the dual structural mechanisms underlying SetA’s coordination of substrate glucosylation and membrane association, providing a spatiotemporal framework for understanding Legionella’s early infection strategy.