β-propellers that bind polyphosphoinositides (PROPPINs) are conserved autophagy effectors that recognize PI3P and PI(3,5)P2 to coordinate membrane remodeling. In budding yeast, Atg18 and Atg21 function at the phagophore/isolated membrane during macroautophagy, whereas the role of the less characterized PROPPIN Hsv2 has remained unclear. Here we demonstrate that Hsv2 is required for rapamycin-induced bulk microautophagy and for micronucleophagy. Loss of HSV2 attenuated processing of the vacuolar membrane reporter GFP-Pho8 and impaired the nucleolar protein reporter Nop1-GFP degradation under Atg1-deficient conditions. Upon TORC1 inactivation, Hsv2 accumulated as puncta on the vacuolar membrane where it colocalized with ESCRT components. An amphipathic-helix deletion mutant of Hsv2 failed to localize to the vacuolar membrane and exhibited diminished microautophagy, highlighting the importance of helix-dependent membrane association. Hsv2 also colocalized with the bridge-like lipid transfer protein Atg2, and deletion of ATG2, but not ATG1, reduced bulk microautophagy, suggesting a specific requirement for the Hsv2-Atg2 axis. These findings uncover a role for Hsv2 in microautophagy and suggest that the Hsv2-Atg2 complex promotes lipid supply to ESCRT-deforming sites on the vacuolar membrane, thereby sustaining membrane invagination and substrate engulfment.

• PMID: 41806572
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Journal Article | Research Support, Non-U.S. Gov't

Authors

Yasumori K, Ushimaru T

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