WIPI2

WIPI2 is a PI3P-binding β-propeller protein that serves as the central effector linking PI3P generation to LC3/ATG8 lipidation during autophagosome biogenesis (PMID:20505359, PMID:24954904). Upon autophagy induction, PI3P produced on phagophore-associated membranes recruits WIPI2, which directly binds ATG16L1 and recruits the ATG12–5–16L1 E3-like complex to the phagophore to drive LC3 conjugation; ATG16L1 mutants that retain FIP200 binding but cannot bind WIPI2 fail to support starvation-induced autophagy (PMID:24954904). Complete reconstitution on giant unilamellar vesicles established that this recruitment is strictly PI3P-dependent and that WIPI2 allosterically activates the E3 complex—simply targeting the E3 to membranes is insufficient—while PI3KC3-C1 and WIPI2 reinforce each other's membrane recruitment in a positive feedback loop that accelerates lipidation kinetics (PMID:32437499, PMID:38324698). Structurally, the ATG16L1 W2IR helix docks in an electropositive groove between WIPI2 β-propeller blades 2 and 3, and a second binding site (WBS2) conserved from yeast to mammals contributes to the interaction; both sites are required for normal autophagic flux (PMID:34505572, PMID:37165562). WIPI2 is recruited to multiple membrane platforms including omegasomes and RAB11A-positive recycling endosomes, the latter serving as a primary platform for autophagosome formation and mitophagy (PMID:20505359, PMID:29634932). WIPI2 abundance is tightly regulated: mTORC1 phosphorylates WIPI2 at Ser395 to direct it to the HUWE1 E3 ligase for proteasomal degradation, coupling nutrient status to autophagic capacity, and during mitosis CRL4–DDB1 ubiquitinates WIPI2 to suppress autophagy (PMID:30340022, PMID:30898011). Beyond canonical starvation autophagy, WIPI2 mediates antibacterial autophagy of Salmonella downstream of TBK1 (PMID:24954904, PMID:27370208), is engaged by STING via competitive binding to its FRRG motif to drive PI3P-independent autophagy and cytoplasmic DNA clearance (PMID:36872914), and promotes mitophagy by recruiting VCP/p97 to damaged mitochondria and interacting with the Nix MER domain (PMID:35389758, PMID:37621214). A homozygous WIPI2 missense mutation in its phosphoinositide-binding region causes a neurodevelopmental disorder, with patient fibroblasts showing reduced ATG16L1 binding, LC3 lipidation, and autophagic flux (PMID:30968111).

1. 2004 Medium

   Established the pathway position of the WIPI2 ortholog by showing it is required for ATG8 lipidation and recruitment of the conjugation machinery, defining a conserved role upstream of ATG8 conjugation.

   Evidence Genetic deletion, GFP-Atg8 imaging, and lipidation assays in yeast Atg21

   PMID:15155809

   Open questions at the time

   • Did not define the direct binding partner mediating recruitment
   • Yeast Cvt pathway context, not mammalian starvation autophagy
2. 2010 High

   Placed mammalian WIPI2 downstream of PI3P synthesis and upstream of autophagosome maturation, showing its loss arrests omegasome-stage structures.

   Evidence siRNA knockdown and co-localization imaging with autophagy markers in mammalian cells

   PMID:20505359

   Open questions at the time

   • Direct molecular partner of WIPI2 not yet identified
   • Mechanism of E3 recruitment unresolved
3. 2010 Medium

   Demonstrated the FRRG phosphoinositide-binding motif is required for ortholog function and that it scaffolds Atg8 and Atg16 localization while protecting Atg8-PE from premature Atg4 cleavage.

   Evidence FRRG motif mutagenesis and lipidation assays in yeast Atg21

   PMID:20154084

   Open questions at the time

   • Direct vs indirect recruitment of Atg16 not distinguished here
   • Yeast ortholog, mammalian relevance inferred
4. 2014 High

   Identified the direct WIPI2b–ATG16L1 interaction as the mechanism by which a PI3P effector recruits the E3-like conjugation complex, the key molecular link between PI3P and LC3 lipidation.

   Evidence Co-IP, pulldown, interface mutagenesis, ectopic membrane targeting, and depletion phenotypes for both starvation and Salmonella autophagy

   PMID:24954904

   Open questions at the time

   • Whether WIPI2 merely tethers or allosterically activates the E3 not yet resolved
   • Structural basis of interface unknown
5. 2015 High

   Defined how the ortholog scaffolds both the E3 complex and Atg8 simultaneously, binding Atg16 via its coiled-coil and Atg8 via a non-AIM motif that leaves the AIM site free for Atg3.

   Evidence Co-IP, pulldown, yeast two-hybrid, and mutagenesis in yeast Atg21

   PMID:25691244

   Open questions at the time

   • Membrane orientation of the scaffold not defined
   • Mammalian Atg8 binding not directly tested
6. 2018 High

   Connected nutrient signaling to WIPI2 stability by showing mTORC1 phosphorylates Ser395 to trigger HUWE1-mediated degradation, providing a switch that gates autophagic capacity.

   Evidence In vitro kinase assay, phosphosite mapping, ubiquitination assay, and in vivo mouse liver fasting/HUWE1 silencing

   PMID:30340022

   Open questions at the time

   • How Ser395 phosphorylation promotes HUWE1 binding structurally unknown
   • Other kinases/phosphatases not explored
7. 2018 High

   Identified RAB11A-positive recycling endosomes as a direct membrane platform for WIPI2 recruitment and autophagosome formation, broadening the membrane sources for canonical autophagy.

   Evidence Reciprocal Co-IP, live-cell imaging, and RAB11A knockout phenotyping

   PMID:29634932

   Open questions at the time

   • Relative contribution of RAB11A vs omegasome platforms unquantified
   • Whether RAB11A binding is direct or PI3P-mediated not fully resolved
8. 2020 High

   Reconstitution proved that WIPI2 allosterically activates the ATG12-5-16L1 E3 and engages PI3KC3-C1 in positive feedback, distinguishing active catalysis from passive tethering.

   Evidence Complete LC3 lipidation reconstitution on GUVs with ectopic E3 targeting and feedback assays

   PMID:32437499

   Open questions at the time

   • Structural basis of allosteric activation not defined here
   • In vivo feedback kinetics not measured
9. 2020 High

   Localized the ortholog to the phagophore edge at the vacuole–isolation membrane contact site and established Atg16 binds the bottom face of the propeller, fixing the scaffold's membrane orientation.

   Evidence Crystal structure of Atg21–Atg16 coiled-coil, FRAP/FCCS imaging, and Vac8 deletion in yeast

   PMID:32515645

   Open questions at the time

   • Mammalian VICS equivalent not established
   • Vac8 mammalian counterpart unknown
10. 2021 High

    Provided the atomic structure of the WIPI2d–ATG16L1 W2IR interface in the groove between blades 2 and 3, defining the WIPI1/2 W2IR subclass distinct from the WIPI3/4 ATG2-binding subclass.

    Evidence 1.85 Å crystal structure with interface mutagenesis validated in vitro and in cells

    PMID:34505572

    Open questions at the time

    • Second binding site not yet characterized
    • Conformational changes upon membrane binding not captured
11. 2023 High

    Revealed a second ATG16L1 binding site (WBS2) conserved across evolution, showing the WIPI2–ATG16L1 interaction is bipartite and both sites are needed for flux.

    Evidence Crystal structures of both WBS1 and WBS2 complexes, ITC, and cell-based flux assays

    PMID:37165562

    Open questions at the time

    • Functional cooperativity between the two sites not quantified
    • Whether both engage simultaneously on membranes unknown
12. 2023 High

    Established a non-canonical, PI3P-independent recruitment route via STING competing with PI3P for the WIPI2 FRRG motif, linking WIPI2 to innate immune DNA clearance.

    Evidence Co-IP, FRRG mutagenesis, competition binding, and cytoplasmic DNA clearance assays

    PMID:36872914

    Open questions at the time

    • Structural basis of STING–FRRG binding not solved
    • In vivo relevance of mutual inhibition not tested
13. 2023 Medium

    Identified direct recruitment of WIPI2 to mitochondria by the Nix MER domain independent of the LIR motif, defining a receptor-driven route for WIPI2 in mitophagy.

    Evidence Chemically induced dimerization, Co-IP, imaging, and mitophagy assays

    PMID:37621214

    Open questions at the time

    • Single lab, not independently confirmed
    • Structural basis of MER–WIPI2 binding unknown
14. 2024 Medium

    Resolved the stepwise mechanics of LC3 lipidation downstream of WIPI2 recruitment, defining membrane engagement by ATG16L1 and ATG3 and PE concentration at the catalytic site.

    Evidence Molecular dynamics simulations combined with in vitro reconstitution and cell-based assays

    PMID:38324698

    Open questions at the time

    • Mechanistic details partly computational
    • Catalytic histidine roles not validated by structure
15. 2019 Medium

    Linked WIPI2 dysfunction to human disease, showing a phosphoinositide-binding region mutation impairs ATG16L1 binding and autophagy and causes a neurodevelopmental disorder.

    Evidence Whole-exome sequencing, GFP pulldown of disease mutant, and patient fibroblast functional assays

    PMID:30968111

    Open questions at the time

    • Single family/patient cohort
    • Tissue-specific mechanism of neurodevelopmental phenotype unresolved

• How the multiple competing recruitment routes (PI3P, STING, RAB11A, Nix MER), the dual ATG16L1 sites, and the layered degradation controls are integrated to set the timing and location of autophagosome formation in different physiological contexts remains unresolved.
• No unified quantitative model coordinating recruitment platforms
• Crosstalk between mTORC1/HUWE1 and CRL4 degradation pathways unknown
• Cell-type-specific contributions, e.g. in neurons, not mechanistically dissected