# Proximity Labeling Reveals RNA-Binding Proteins Associating with the Human Mitochondrial Import Receptor TOMM20

## TL;DR

This study uses proximity labeling to identify RNA-binding proteins that associate with the mitochondrial receptor TOMM20 in human cells.

## Contribution

The novel use of APEX2-based proximity labeling reveals specific RNA-binding proteins linked to TOMM20, suggesting a role in translation stress response.

## Key findings

- Several RNA-binding proteins preferentially associate with TOMM20 over TOMM70 in HeLa cells.
- Inhibiting translation increases the association of these proteins with TOMM20.
- TOMM20 may help maintain cellular homeostasis during translation stress by retaining protective proteins at the mitochondrial membrane.

## Abstract

The import of most mitochondrial proteins requires that
their precursor
proteins be bound by the peripheral receptor proteins TOM20, TOM22,
and TOM70. Budding yeast TOM20 and TOM70 have been extensively studied
regarding their interaction partners and recognized substrates; however,
little data is available for metazoan cells. Using APEX2-based proximity
labeling, we created association profiles for human TOMM20 and TOMM70
in HeLa cells. We focused particularly on their interactions with
RNA-binding proteins (RBPs) because there is evidence of RNA association
with the mitochondrial outer membrane (MOM) and of local translation
at the mitochondrial surface, however, these processes are poorly
understood. Our results demonstrate that several RBPs and translation
factors preferentially associate with TOMM20 rather than TOMM70. These
include SYNJ2BP, a previously identified membrane-bound RBP that binds
and protects mRNA encoding mitochondrial proteins. Inhibiting translation
with puromycin increased the association of these RBPs with TOMM20
compared to TOMM70. This suggests that TOMM20, but not TOMM70, may
play a role in maintaining cellular homeostasis during translation
stress by retaining protective RBPs and translation-related proteins
at the MOM.