9.A.79. The Autophagosomal Phospholipid Transmembrane Translocase (Atg9) Family
Orii et al. 2021 found that Atg9 translocates phospholipids across liposomal membranes and proposed that this function plays an essential role in the expansion of membranes. The distribution of phosphatidylinositol 3-phosphate in both leaflets of yeast autophagosomal membranes supports this proposal, but if Atg9-mediated lipid transport is crucial, symmetrical distribution in autophagosomes should be found broadly for other phospholipids. Therefore, Orii et al. 2021 analyzed the distributions of phosphatidylcholine, phosphatidylserine, and phosphatidylinositol 4-phosphate by freeze-fracture electron microscopy and found that these phospholipids are distributed with comparable densities in the two leaflets of autophagosomes and autophagic bodies. Moreover, de novo-synthesized phosphatidylcholine is incorporated into autophagosomes preferentially and shows a symmetrical distribution in autophagosomes within 30 min after synthesis, whereas this symmetrical distribution is compromised in yeast expressing an Atg9 mutant. Thus, transbilayer phospholipid movement that is mediated by Atg9 is involved in the biogenesis of autophagosomes. Backbone NMR assignments of the nucleotide binding domain of BmrA in the post-hydrolysis state have been determined (Coudevylle et al. 2022).