A study of the role of the Atg8 protein in autophagic vesicle formation

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Autophagy is the term used to refers to an catabolic cellular cleanup process through the lysosomal machinery. During autophagy portions of cytoplasm are non-selectively sequestered in unique double membrane bound vesicles called autophagosomes that are transported to vacuole for degradation. The end products of catabolism are reused by the cell. The formation of autophagosomes is catalyzed by a concerted action of core machinery proteins. Among the core machinery proteins is a ubiquitin like cytosolic protein, Atg8. In yeast, Saccharomyces cerevisiae, Atg8 is induced during starvation. Atg8 is conjugated to a lipid, phosphoethanolamine. (PE). PE conjugated Atg8 tightly binds to the autophagic membrane and is widely used as marker for autophagy. The exact in vivo function of Atg8 is less well understood. In this study, we focused on how Atg8 functions in the formation of autophagosomal membrane and demonstrated that (1) The deconjugation of Atg8 from PE is essential for completion of autophagosome formation (2) Deconjugation of Atg8-PE requires Atg4 protease; (3) presence of Atg18 protein is essential for deconjugation during starvation. Here we present substantial evidence that the delipidation of Atg8 is required for the completion of the formation of autophagosomes. We also show that lipidation and delipidation of Atg8 is a highly dynamic process that is regulated by stress.