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Publications of the Week

Insights on Autophagosome–Lysosome Tethering from Structural and Biochemical Characterization of Human Autophagy Factor EPG5

By March 23, 2021No Comments

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This week we profile a recent publication in Communications Biology from the
laboratory of Dr. Calvin Yip (pictured, second from right) at UBC.

Can you provide a brief overview of your lab’s current research focus?

One of our lab’s current research focuses is to delineate the molecular mechanism of an evolutionarily conserved pathway called autophagy. As the major pathway for the removal and recycling of intracellular materials and organelles, autophagy plays a central role in the maintenance of cellular homeostasis. Autophagy malfunction has been linked to neurodegeneration, cancers, inflammatory bowel diseases, and other chronic human diseases. Autophagy degradation operates in a multi-step fashion. It begins with the sequestration of cargo into a double-membrane transport vesicle called the autophagosome. This cargo-laden autophagosome is subsequently delivered to the “cellular incinerator”, the lysosome, for breakdown. Since the inception of our lab in 2011, we have been using a multi-pronged approach combining protein biochemistry, structural biology, and cell biology to characterize different proteins and protein complexes that mediate the different steps of autophagy.

What is the significance of the findings in this publication?

The focus of this publication is a recently identified metazoan autophagy factor known as EPG5. This an extraordinarily large protein (at ~290kDa) has been implicated to play a key role in terminal step of autophagy where the cargo-laden autophagosome docks and fuses with the lysosome. However, precisely how EPG5 exerts its physiological function is not fully understood. Interestingly, mutations to the gene encoding EPG5 in humans lead to a severe multi-system disorder known as Vici syndrome. Yet, how these mutations disrupt the molecular function of EPG5 remains poorly defined. To address these questions, our lab established a procedure to produce recombinant human EPG5 and this enabled us to characterize the structural and biochemical properties of this large-sized protein. Using electron microscopy, we were able to visualize the overall architecture of human EPG5 which has an overall shape resembling a shepherd’s staff. We also uncovered that human EPG5 preferentially binds to a group of proteins known as GABARAP’s which localize to the surface of autophagosomes. Using X-ray crystallography, we visualized how at the atomic level how the so-called LIR domain of human EPG5 engages in interaction with GABARAP. Lastly, with the assistance from our collaborator Dr. Michael Lazarou at Monash University, we demonstrated that EPG5-GABARAP interaction is critical to mitophagy or the specifically removal of damaged mitochondria by autophagy.

Briefly, what are the next steps for this research?

The studies described in this publication enabled us to establish an experimental platform for investigating the effects of how Vici syndrome mutations affect the structure and function of EPG5. Using an exhaustive list of Vici syndrome mutations compiled from our clinical collaborators, we will begin generating and characterizing the biochemical and structural properties of a series of mutant human EPG5. Knowledge gained from this work will help us obtain a more comprehensive understanding of the molecular ethology of Vici syndrome and pave the way for developing therapeutic approaches against this devastating rare disease.

This research was supported by:

A CIHR Foundation Grant and a CIHR Project Grant.

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