Structural basis of p62/SQSTM1 helical filaments and their role in cellular cargo uptake

Wim J H Hagen,Matthias Wilmanns,Tanja Kuhm,Arjen J Jakobi,Terje Johansen,Simon A Mortensen,Carsten Sachse,Anthimi Palara,Sebastian W Schultz,Birendra Kumar Shrestha,Stefan T Huber,Trond Lamark,Andreas Brech

doi:10.1038/s41467-020-14343-8

Abstract

p62/SQSTM1 is an autophagy receptor and signaling adaptor with an N-terminal PB1 domain that forms the scaffold of phase-separated p62 bodies in the cell. The molecular determinants that govern PB1 domain filament formation in vitro remain to be determined and the role of p62 filaments inside the cell is currently unclear. We here determine four high-resolution cryo-EM structures of different human and Arabidopsis PB1 domain assemblies and observed a filamentous ultrastructure of p62/SQSTM1 bodies using correlative cellular EM. We show that oligomerization or polymerization, driven by a double arginine finger in the PB1 domain, is a general requirement for lysosomal targeting of p62. Furthermore, the filamentous assembly state of p62 is required for autophagosomal processing of the p62-specific cargo KEAP1. Our results show that using such mechanisms, p62 filaments can be critical for cargo uptake in autophagy and are an integral part of phase-separated p62 bodies.

Highlights

P62/SQSTM1 is an autophagy receptor and signaling adaptor with an N-terminal PB1 domain that forms the scaffold of phase-separated p62 bodies in the cell
The PB1 domain is a common interaction module present in all kingdoms of life and found in various proteins involved in membrane trafficking, redox regulation, cell division, as well as in signaling
We focused on the structure in addition to the biological and functional relevance of the p62-PB1 domain in the context of polymeric assemblies

Summary

Introduction

P62/SQSTM1 is an autophagy receptor and signaling adaptor with an N-terminal PB1 domain that forms the scaffold of phase-separated p62 bodies in the cell. P62 has a tendency to cluster, and in human cells, is often observed in discrete punctae known as p62 bodies[2] The formation of these bodies is dependent on the amino-terminal PB1 domain of p622. PB1 domains are protein interaction modules with critical roles in the assembly of protein complexes involved in autophagy, signaling, cell division, and redox processes[3], as well as the auxinresponse pathway in plants[4]. PB1 domains form homotypic interactions via conserved electrostatic motifs molded by basic or acidic surface patches on opposite faces of their ubiquitin-like βgrasp fold[2,5]. Terminal UBA domain of p62 captures ubiquitinated cargo, and the LIR motif guides the cargo–receptor complex to Atg8/LC3, which is anchored to the surface of the autophagosomal membrane[14,15]

Methods

Findings

Conclusion