The Role of the Lipid Flippase Drs2 in Regulating the Transport of Atg9 Vesicles during Selective Autophagy

Core Concepts

The lipid flippase Drs2 interacts with the multisubunit tethering complex TRAPPIII to stabilize it on membranes loaded with the autophagy protein Atg9, which is essential for the biogenesis of Atg9 vesicles and the progression of selective autophagy.

Abstract

The content explores the interplay between multisubunit tethering complexes (MTCs) and lipid flippases, focusing on the role of the P4-ATPase Drs2 in regulating the transport of Atg9 vesicles during selective autophagy.
The key highlights are:

A systematic screen identified interactions between MTCs involved in Golgi trafficking and P4-ATPases, a family of lipid transporters.
The interaction between the TRAPPIII complex and the lipid flippase Drs2 is essential for the biogenesis of Atg9 vesicles and the progression of the CVT pathway, a model for selective autophagy.
The I(S/R)TTK motif in the N-terminal tail of Drs2 mediates the binding to TRAPPIII and is required for Drs2's role in Atg9 trafficking, independent of Drs2's known functions in lipid translocation.
Drs2 stabilizes TRAPPIII on membranes loaded with Atg9, which is necessary for the release of Atg9 vesicles from Atg9 reservoirs, a step that precedes the delivery of Atg9 to the pre-autophagosomal structure.
The interaction between Drs2 and TRAPPIII is regulated by temperature, suggesting that the cell modulates this interplay in response to environmental cues.

Stats

The processing of the aminopeptidase Ape1 is inhibited by 88.5% in drs2Δ cells compared to wild-type cells at 23°C.
In pep4Δdrs2Δ cells, no CVT body-like structures could be detected in the vacuole, unlike in 89.3% of pep4Δ cells.
91.4% of Ape1-GFP aggregates in drs2Δ cells correlated with ribosome exclusion areas devoid of double membrane or CVT vesicle-like structures.

Quotes

"Binding to the N-terminal tail of Drs2 stabilizes TRAPPIII on membranes loaded with Atg9 and it is required for the delivery of Atg9 during selective autophagy, a role that is independent of previously reported functions of the P4-ATPase."
"The I(S/R)TTK motif is conserved in other flippases and is crucial to sustain the network of interactions between Drs2 and MTCs, including GARP, TRAPPII and TRAPPIII."
"The enhancement of the Drs2-TRAPPIII module assembly in response to temperature decrease indicates that the interaction between Drs2 and TRAPPIII is subjected to regulation in response to environmental cues."

Key Insights Distilled From

Drs2 regulates TRAPPIII in Atg9 transport: exposing the interplay of P4-ATPases and Multisubunit Tethering Complexes

by Pazos Capell... at www.biorxiv.org 12-26-2020

https://www.biorxiv.org/content/10.1101/2020.12.25.417865v3

Deeper Inquiries

How might the regulation of the Drs2-TRAPPIII interaction in response to temperature changes be integrated with other cellular pathways to modulate selective autophagy

The regulation of the Drs2-TRAPPIII interaction in response to temperature changes could be integrated with other cellular pathways to modulate selective autophagy through a coordinated response to environmental cues. For example, cells might sense temperature variations as a stress signal, leading to the activation of specific signaling pathways that modulate the interaction between Drs2 and TRAPPIII. This could involve the activation of temperature-sensitive kinases or phosphatases that directly phosphorylate or dephosphorylate key residues in Drs2 or TRAPPIII, influencing their binding affinity. Additionally, temperature changes could alter the lipid composition of membranes, affecting the localization and activity of Drs2 and TRAPPIII. This dynamic regulation of the Drs2-TRAPPIII interaction in response to temperature fluctuations could fine-tune the transport of Atg9 vesicles, ensuring efficient selective autophagy under varying environmental conditions.

What other cellular processes beyond selective autophagy could be impacted by the interplay between Drs2 and MTCs, and how might this contribute to our understanding of lipid homeostasis and vesicle trafficking

The interplay between Drs2 and MTCs, including TRAPPIII, could impact various cellular processes beyond selective autophagy, contributing to our understanding of lipid homeostasis and vesicle trafficking. One such process could be the regulation of membrane biogenesis and maintenance, as the interaction between Drs2 and MTCs likely influences lipid composition and distribution within cellular membranes. This could have implications for organelle identity, membrane dynamics, and intracellular trafficking pathways. Additionally, the coordination between Drs2 and MTCs may play a role in protein sorting and vesicle targeting, affecting the efficiency of intracellular transport and secretion. The modulation of lipid transport and vesicle trafficking by the interplay between Drs2 and MTCs could have broad implications for cellular homeostasis and organelle function.

Given the conservation of the I(S/R)TTK motif in P4-ATPases, could this structural feature play a broader role in coordinating lipid transport with the activity of other trafficking machineries across eukaryotes

The conservation of the I(S/R)TTK motif in P4-ATPases suggests that this structural feature may play a broader role in coordinating lipid transport with the activity of other trafficking machineries across eukaryotes. This motif could serve as a key determinant for the interaction between P4-ATPases and MTCs, facilitating the regulation of vesicle trafficking and lipid homeostasis in various cellular contexts. The presence of the I(S/R)TTK motif in multiple P4-ATPases implies a conserved mechanism for mediating protein-protein interactions and membrane dynamics in different organisms. This motif may act as a molecular switch that modulates the function of P4-ATPases in response to specific cellular signals or environmental cues, allowing for the precise control of lipid transport and vesicle trafficking pathways. The broader role of the I(S/R)TTK motif in coordinating lipid transport and membrane dynamics highlights its significance in cellular physiology and organelle function.