EFR3B

EFR3B is a palmitoylated peripheral plasma membrane protein that serves as the membrane anchor recruiting the lipid kinase PI4KA to the plasma membrane, where it governs phosphoinositide homeostasis (PMID:34663815, PMID:39705356). It does so as a component of the plasma membrane PI4KA complex containing PI4KA, TTC7B, and FAM126A, with its C-terminus undergoing a disorder-to-order transition upon binding to make direct contacts with both TTC7B and FAM126A; complex-disrupting mutations in EFR3, TTC7B, or FAM126A reduce PI4KA recruitment to the plasma membrane (PMID:39705356). This recruitment is regulated by two layers of post-translational control: differential palmitoylation of a tri-cysteine motif (Cys5/Cys7/Cys8) creates distinct lipoforms that control both EFR3B partitioning between liquid-ordered and liquid-disordered membrane domains and its interaction with TMEM150A to tune PI(4,5)P2 resynthesis after PLC signaling (PMID:34569608), and phosphorylation of EFR3B markedly decreases its affinity for TTC7–FAM126, providing a switch that downregulates PI4KA membrane recruitment (PMID:41197736). Through control of plasma membrane phosphoinositide signaling, EFR3B (with EFR3A) contributes to the desensitization and phosphorylation state of AT1a angiotensin receptors and the sustained Ca2+ response to angiotensin II (PMID:25380825). In the brain, EFR3B acts cell-autonomously to maintain the excitability of CA2 hippocampal pyramidal neurons required for social novelty recognition (PMID:38190534).

1. 2014 Medium

   Established a cellular function for EFR3 proteins in GPCR signaling, showing they constrain receptor desensitization rather than acting as inert membrane proteins.

   Evidence siRNA double-knockdown of EFR3A/EFR3B with Ca2+, receptor phosphorylation, and Gq desensitization readouts in HEK293 cells

   PMID:25380825

   Open questions at the time

   • Did not resolve the molecular intermediary linking EFR3 to receptor phosphorylation state
   • Redundancy between EFR3A and EFR3B not dissected
   • Direct binding partners not identified
2. 2021 High

   Placed EFR3B within the plasma membrane PI4KA complex and linked its assembly to palmitoylation and to calcineurin-mediated dephosphorylation of FAM126A, defining a regulated lipid-kinase recruitment module.

   Evidence Palmitoylation-dependent Co-IP, HDX-MS, calcineurin substrate assay, and PI4P production measurement during GPCR signaling

   PMID:34663815

   Open questions at the time

   • Structural basis of EFR3B contacts within the complex not yet resolved
   • Did not establish EFR3B's own phosphoregulation
3. 2021 High

   Demonstrated that differential palmitoylation of an EFR3B tri-cysteine motif encodes distinct lipoforms controlling membrane-domain partitioning and TMEM150A interaction, connecting lipid modification to PI(4,5)P2 resynthesis.

   Evidence Mutagenesis of palmitoylation sites, Co-IP with TMEM150A, membrane partitioning and phosphoinositide homeostasis assays

   PMID:34569608

   Open questions at the time

   • Enzymes setting the differential palmitoylation pattern not identified
   • Quantitative coupling between lipoform and downstream PI4P output not fully defined
4. 2024 High

   Resolved the structural mechanism of recruitment, showing the EFR3 C-terminus folds upon binding to contact both TTC7B and FAM126A and that interface mutations reduce PI4KA membrane targeting.

   Evidence Cryo-EM, HDX-MS, mutational interface analysis, and plasma membrane recruitment assays (peer-reviewed PMID:39705356; preprint PMID:38746453)

   PMID:38746453 PMID:39705356

   Open questions at the time

   • Structural work conducted largely on EFR3A with extension to EFR3B by homology
   • Does not address how palmitoylation modulates the ordered C-terminal contact
5. 2024 High

   Defined a cell-autonomous in vivo role for EFR3B in maintaining CA2 pyramidal neuron excitability and social novelty recognition, linking the molecular module to a circuit-level behavior.

   Evidence Conditional knockout, region-specific knockdown, re-expression rescue, chemogenetic activation, electrophysiology and behavioral testing in mouse

   PMID:38190534

   Open questions at the time

   • Did not directly tie the behavioral phenotype to PI4KA/phosphoinositide signaling in CA2 neurons
   • Effector channels or pathways downstream of EFR3B in CA2 neurons unidentified
6. 2025 High

   Identified phosphorylation of EFR3B as a regulatory switch that lowers its affinity for TTC7–FAM126, and quantified isoform-specific binding hierarchies governing PI4KA recruitment strength.

   Evidence Binding affinity measurements across EFR3/TTC7/FAM126 combinations, phosphorylation assays, cryo-EM, HDX-MS, nanobody competition, and bilayer/cell-based PI4P assays

   PMID:41197736

   Open questions at the time

   • Kinase(s) phosphorylating EFR3B in vivo not identified
   • Physiological context where this switch operates not defined

• How EFR3B's palmitoylation-, phosphorylation-, and TMEM150A-dependent regulation of PI4KA is integrated to produce the neuronal excitability and behavioral phenotypes remains unresolved.
• No demonstration that phosphoinositide signaling underlies the CA2 excitability defect
• Tissue-specific upstream regulators of EFR3B modification unknown