# A Rab1 interactome illuminates a dual role in autophagy and membrane trafficking

## TL;DR

This study reveals new roles for Rab1 in autophagy and membrane trafficking by identifying its interacting proteins, including a dynein motor adaptor and autophagy cargo receptors.

## Contribution

The paper expands the Rab1 interactome and shows that Rab1 interacts with dynein and autophagy cargo receptors, revealing its dual role in membrane trafficking and autophagy.

## Key findings

- Rab1 interacts with dynein adaptor FHIP2A, which is membrane-dependent and explains dynein recruitment to the ER-Golgi intermediate compartment.
- Rab1 interacts with autophagy cargo receptors, including optineurin, which is essential for mitophagy in vivo.
- Proximity biotinylation (MitoID) identified novel Rab1 interactors, highlighting limitations of conventional methods in capturing GTPase effectors.

## Abstract

The small GTPase Rab1 is a master regulator of Golgi traffic and autophagy. A proteomic screen identifies novel Rab1 effectors, including a dynein motor adaptor and cargo receptors for autophagy.

The small GTPase Rab1 is found in all eukaryotes and acts in both ER-to-Golgi transport and autophagy. Several Rab1 effectors and regulators have been identified, but the mechanisms by which Rab1 orchestrates these distinct processes remain incompletely understood. We apply MitoID, a proximity biotinylation approach, to expand the interactome of human Rab1A and Rab1B. We identify new interactors among known membrane traffic and autophagy machinery, as well as previously uncharacterized proteins. One striking set of interactors are the cargo receptors for selective autophagy, indicating a broader role for Rab1 in autophagy than previously supposed. Two cargo receptor interactions are validated in vitro, with the Rab1-binding site in optineurin being required for mitophagy in vivo. We also find an interaction between Rab1 and the dynein adaptor FHIP2A that can only be detected in the presence of membranes. This explains the recruitment of dynein to the ER-Golgi intermediate compartment and demonstrates that conventional methods can miss a subset of effectors of small GTPases.