SH3GLB2

SH3GLB2 (endophilin B2) is an N-BAR domain-containing endophilin family protein that functions as a positive regulator of endosome maturation and intracellular membrane trafficking (PMID:28455444). It was first identified as a binding partner of endophilin B1 (SH3GLB1), forming homo- and heterodimers through a core coiled-coil region rather than its SH3 domain, and localizes to the cytoplasm where it is excluded from the nucleus (PMID:11161816). Through its N-BAR domain-mediated control of membrane curvature, SH3GLB2 promotes endosome acidification and downstream events including EGFR degradation, autophagic flux, and influenza A viral RNA nuclear entry, while leaving endocytic internalization and lysosomal function intact (PMID:28455444). Despite a localization and tissue distribution resembling endophilin B1 and colocalization with Bax, SH3GLB2 is dispensable for mitochondrial and Bax-mediated apoptosis (PMID:11161816, PMID:28455444). In vivo, loss of SH3GLB2 enhances recovery from severe H1N1 influenza infection, accompanied by induction of surfactant and alveolar genes and restoration of alveolar macrophages and CD4+ lymphocytes, indicating a role in lung homeostasis and alveolar immune cell recovery (PMID:28779131).

1. 2001 Medium

   Established that SH3GLB2 is a cytoplasmic endophilin-family protein that dimerizes with SH3GLB1 through a defined structural element, framing it as a partner within the endophilin B system rather than an SH3-dependent adaptor.

   Evidence Yeast two-hybrid screen with domain mapping and subcellular localization

   PMID:11161816

   Open questions at the time

   • Functional consequence of the B1–B2 dimer not addressed
   • No biochemical reconstitution of the coiled-coil interaction
   • Cellular process served by the dimer unknown
2. 2001 Medium

   Tested and excluded an apoptotic role despite Bax colocalization, ruling out a direct effect of SH3GLB2 on Bax-mediated cell death.

   Evidence Overexpression in HeLa and 293T cells with apoptosis assay (negative result)

   PMID:11161816

   Open questions at the time

   • Overexpression may not reflect endogenous function
   • Did not exclude apoptosis roles in other contexts
3. 2017 High

   Defined the core cellular function of SH3GLB2 as a positive regulator of endosome maturation, linking its N-BAR membrane-curvature activity to acidification, receptor degradation, autophagy, and viral replication.

   Evidence Genetic knockout cells/mice with endosome acidification, EGFR degradation, autophagic flux, and viral RNA nuclear entry assays

   PMID:28455444

   Open questions at the time

   • Direct demonstration of N-BAR membrane binding/curvature on endosomal membranes not shown
   • Molecular partners coupling SH3GLB2 to the acidification machinery unidentified
   • Whether the B1–B2 dimer mediates this function untested
4. 2017 Medium

   Confirmed via genetic knockout that SH3GLB2 is dispensable for mitochondrial apoptosis, distinguishing it functionally from endophilin B1 despite shared localization.

   Evidence Genetic knockout with apoptosis assay (negative result)

   PMID:28455444

   Open questions at the time

   • Functional divergence from endophilin B1 not mechanistically explained
5. 2017 High

   Extended SH3GLB2 function to organismal physiology, showing that its loss improves recovery from influenza and restores alveolar homeostasis and immune cells, implicating it in lung tissue and immune recovery.

   Evidence B2-deficient mouse model with intranasal H1N1 infection, flow cytometry, gene expression analysis, and respiratory mechanics

   PMID:28779131

   Open questions at the time

   • Whether the protective phenotype derives from the endosome-maturation/viral-entry role is not directly connected
   • Cell-type responsible for the lung phenotype not resolved
6. 2022 Low

   Placed SH3GLB2 aggregation within neurodegeneration-associated protein cascades downstream of TRAPPC6AΔ and TIAF1 in neurotoxin-treated neurons, and in AD models.

   Evidence MPP+ treatment and aggregation assays in SK-N-SH cells; 3xTg AD mouse aggregation studies

   PMID:29067327 PMID:36498839

   Open questions at the time

   • Pathway placement inferred from co-aggregation without direct epistasis
   • Mechanism of SH3GLB2 itself in aggregation not dissected
   • Causal contribution to neurodegeneration unestablished

• How SH3GLB2's N-BAR membrane-remodeling activity mechanistically drives endosome acidification, and whether its dimerization with SH3GLB1 is required for this function, remain unresolved.
• No structural model of SH3GLB2 on membranes
• Effectors linking SH3GLB2 to V-ATPase/acidification unknown
• Functional role of the B1–B2 dimer in endosome maturation untested