# Precise Mapping of the Proteasome Interaction Region (PIR) of p62/SQSTM1: Decoupling Condensate Formation from Proteasome Recruitment

## TL;DR

This study identifies a six-amino-acid region in the p62 protein that is crucial for recruiting the proteasome, separating this function from other roles like condensate formation.

## Contribution

The study precisely maps a proteasome-interacting region in p62 and shows it is distinct from regions involved in condensate formation.

## Key findings

- A six-amino-acid stretch (residues 84–89) in p62 is essential for proteasome recruitment.
- Loss of this region impairs proteasome-dependent degradation in p62 condensates.
- The PIR is distinct from regions responsible for condensate assembly and signaling.

## Abstract

What are the main findings?
This study uncovered a discrete and minimal proteasome-interacting region (PIR) within p62, precisely mapped to a six–amino acid stretch (residues 84–89; TMAMSY).The study demonstrates that loss of the PIR selectively disrupts the ability of p62 liquid–liquid phase–separated (LLPS) condensates to recruit 26S proteasome, resulting in impaired proteasome-dependent substrate degradation.

This study uncovered a discrete and minimal proteasome-interacting region (PIR) within p62, precisely mapped to a six–amino acid stretch (residues 84–89; TMAMSY).

The study demonstrates that loss of the PIR selectively disrupts the ability of p62 liquid–liquid phase–separated (LLPS) condensates to recruit 26S proteasome, resulting in impaired proteasome-dependent substrate degradation.

What are the implications of the main finding?
These findings establish p62-mediated LLPS as a critical organizational hub for UPS activity, implying that perturbation of this mechanism may facilitate pathological processes, including neurodegeneration and malignant transformation.Precise identification of the PIR provides a molecular framework for dissecting the multifunctional roles of p62, enabling future studies to uncouple proteasome recruitment from other p62-dependent processes such as autophagy and signaling.

These findings establish p62-mediated LLPS as a critical organizational hub for UPS activity, implying that perturbation of this mechanism may facilitate pathological processes, including neurodegeneration and malignant transformation.

Precise identification of the PIR provides a molecular framework for dissecting the multifunctional roles of p62, enabling future studies to uncouple proteasome recruitment from other p62-dependent processes such as autophagy and signaling.

p62/SQSTM1 is a multifunctional scaffold protein central to selective autophagy and, more recently, recognized as a regulator of ubiquitin–proteasome system-mediated degradation of intracellular proteins. Within phase-separated condensates, p62 has been shown to recruit and sequester the proteasome, yet the molecular basis for this interaction has remained largely unknown. Our previous study demonstrated that the ‘PB1’ domain (residues 1–123) of p62 is necessary for proteasome binding. However, this long stretch is also responsible for other functions of p62, such as condensate assembly and signal transduction. Thus, it was important to define more precisely the region responsible for interaction with the proteasome. In this study, we used systematic deletion variants of p62 and biochemical assays to delineate the minimal sequence within the PB1 domain responsible for proteasome binding. Our analyses revealed a small stretch of six amino acids (residues 84–89) that bind the proteasome and are distinct from the region responsible for condensate formation. Such a precise variant can serve as a useful tool to dissect how p62–proteasome interaction affects selective degradation and probably stress response, separating it from other p62 functions. Overall, this work advances our understanding of the structural determinants underlying p62’s dual role in autophagy and UPS regulation.