Komagataella phaffii Cue5 Piggybacks on Lipid Droplets for Its Vacuolar Degradation during Stationary Phase Lipophagy.

Ravinder Kumar,Ankit Shroff,Taras Y Nazarko

doi:10.3390/cells11020215

Ravinder Kumar, Ankit Shroff + Show 1 more

Open Access

https://doi.org/10.3390/cells11020215

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Abstract

Recently, we developed Komagataella phaffii (formerly Pichia pastoris) as a model for lipophagy, the selective autophagy of lipid droplets (LDs). We found that lipophagy pathways induced by acute nitrogen (N) starvation and in stationary (S) phase have different molecular mechanisms. Moreover, both types of lipophagy are independent of Atg11, the scaffold protein that interacts with most autophagic receptors and, therefore, is essential for most types of selective autophagy in yeast. Since yeast aggrephagy, the selective autophagy of ubiquitinated protein aggregates, is also independent of Atg11 and utilizes the ubiquitin-binding receptor, Cue5, we studied the relationship of K. phaffii Cue5 with differentially induced LDs and lipophagy. While there was no relationship of Cue5 with LDs and lipophagy under N-starvation conditions, Cue5 accumulated on LDs in S-phase and degraded together with LDs via S-phase lipophagy. The accumulation of Cue5 on LDs and its degradation by S-phase lipophagy strongly depended on the ubiquitin-binding CUE domain and Prl1, the positive regulator of lipophagy 1. However, unlike Prl1, which is required for S-phase lipophagy, Cue5 was dispensable for it suggesting that Cue5 is rather a new substrate of this pathway. We propose that a similar mechanism (Prl1-dependent accumulation on LDs) might be employed by Prl1 to recruit another ubiquitin-binding protein that is essential for S-phase lipophagy.

Highlights

Received: 15 December 2021The Cue5 protein belongs to a protein family called CUET
We developed the Komagataella phaffii yeast as a new model for lipophagy, the selective autophagy of lipid droplets (LDs), and showed that, similar to S. cerevisiae lipophagy [14,15,16], the lipophagy in K. phaffii is independent of Atg11 [17]
Since the selective autophagy receptors (SARs) tag their substrates for autophagic degradation, we tested if Cue5 would tag LDs under lipophagy conditions

Summary

Introduction

Received: 15 December 2021The Cue protein belongs to a protein family called CUET. This family includesCue in yeast and toll interacting protein (TOLLIP) in humans. The AIM or LIR (for LC3-interacting region; an acronym commonly used in mammals) is a conserved motif that confers proteins the ability to bind the autophagosomal marker proteins of Atg family, e.g., yeast Atg or human microtubule associated protein 1 light chain 3 beta (MAP1LC3B) [5]. Proteins that possess both the ubiquitin-binding domain and AIM often act as the ubiquitin-binding autophagic receptors or, “ubiquitin-Atg adaptors”, as they facilitate the interaction of ubiquitinated substrates (cargo) with the Atg8-family proteins on the inner surface of autophagosome (vesicular carrier) leading to cargo sequestration and delivery to the vacuole/lysosome for degradation and recycling.

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