| Aspect | Evidence | Key sources (with year) | URL |
|---|---|---|---|
| Identity/domains | Human EMC3 corresponds to UniProt Q9P0I2, also called ER membrane protein complex subunit 3/TMEM111; it is a core transmembrane subunit of the ER membrane protein complex and belongs to the Oxa1/YidC/Alb3 insertase superfamily, consistent with EMC3-family/domain annotation (pqac-00000004, pqac-00000006, pqac-00000007) | Hegde 2022; Pleiner et al. 2020; O'Donnell et al. 2020 | https://doi.org/10.1146/annurev-biochem-032620-104553 ; https://doi.org/10.1126/science.abb5008 ; https://doi.org/10.7554/elife.57887 |
| Localization | EMC3 is an ER membrane protein within the multi-subunit EMC; structurally it sits in the membrane core with EMC6 and contributes to the membrane-embedded insertase. In Drosophila retina, EMC3 co-localizes with the ER marker calnexin, supporting ER localization in vivo (pqac-00000000, pqac-00000005, pqac-00000032) | Pleiner et al. 2020; Hegde 2022; Xiong et al. 2020 | https://doi.org/10.1126/science.abb5008 ; https://doi.org/10.1146/annurev-biochem-032620-104553 ; https://doi.org/10.1038/s41418-019-0378-6 |
| Molecular function/mechanism | EMC3 is a core insertase subunit that, together with EMC6, forms a hydrophilic intramembrane vestibule for insertion of selected transmembrane domains, especially tail-anchored proteins and some N-terminal or terminal helices of multipass proteins. EMC-mediated insertion is energy-independent and aided by membrane thinning and a positively charged patch that lower the energetic barrier for insertion (pqac-00000001, pqac-00000005, pqac-00000007, pqac-00000015) | Pleiner et al. 2020; O'Donnell et al. 2020; Hegde 2022 | https://doi.org/10.1126/science.abb5008 ; https://doi.org/10.7554/elife.57887 ; https://doi.org/10.1146/annurev-biochem-032620-104553 |
| EMC3-specific structural elements | EMC3 is a three-transmembrane, YidC-like bundle that abuts EMC6 at the complex midline; it has a methionine-rich cytosolic loop required for substrate capture/insertion, a conserved hydrophilic vestibule with key basic residues, lumenal-plane helices that may remodel bilayer properties, and a C-terminal three-helix bundle that binds the cytosolic scaffold EMC2 (pqac-00000000, pqac-00000001, pqac-00000006, pqac-00000013) | Pleiner et al. 2020; Hegde 2022; Pleiner et al. 2023 | https://doi.org/10.1126/science.abb5008 ; https://doi.org/10.1146/annurev-biochem-032620-104553 ; https://doi.org/10.1083/jcb.202212007 |
| Client/substrate examples | EMC-dependent clients include tail-anchored SQS/FDFT1 and multipass proteins such as OPRK1, TRAM2, ATP6V0A1, FZD6, SLC43A3, CD9, and SEC61A1; EMC dependence correlates with polar/charged residues in at least one transmembrane domain, and mutagenesis can switch proteins between EMC-dependent and EMC-independent states (pqac-00000005, pqac-00000022, pqac-00000023, pqac-00000024, pqac-00000026) | Pleiner et al. 2020; Tian et al. 2019 | https://doi.org/10.1126/science.abb5008 ; https://doi.org/10.1016/j.celrep.2019.08.006 |
| 2023-2024 key advances | 2023 work showed that EMC selectivity is enforced by a vestibule-entry charge filter centered on conserved EMC3 residues R31 and R180, which repel positively charged tails to reduce ER misinsertion of mitochondrial TA proteins and help enforce the positive-inside rule. 2024 work showed EMC can post-translationally rectify topology of multipass proteins by inserting C-terminal TMDs after ribosome release, expanding EMC function beyond earlier co-/post-translational insertion models (pqac-00000008, pqac-00000009, pqac-00000011, pqac-00000013, pqac-00000016, pqac-00000017, pqac-00000018) | Pleiner et al. 2023; Wu et al. 2024 | https://doi.org/10.1083/jcb.202212007 ; https://doi.org/10.1038/s41594-023-01120-6 |
| Phenotypes/disease relevance | In vivo loss of Emc3 impairs rhodopsin biogenesis and photoreceptor survival across species and causes retinal degeneration phenotypes. In mouse photoreceptors, Emc3 deletion caused rhodopsin mislocalization and rod/cone death; in bipolar-cell conditional knockout mice, Emc3 loss caused age-dependent bipolar-cell degeneration, synaptic disorganization, reduced ERG b-waves, and reactive gliosis, indicating dependence of neural membrane-protein homeostasis on EMC3 (pqac-00000029, pqac-00000030, pqac-00000031, pqac-00000033, pqac-00000034, pqac-00000035) | Xiong et al. 2020; Zhu et al. 2020 | https://doi.org/10.1038/s41418-019-0378-6 ; https://doi.org/10.1371/journal.pone.0238435 |
| Quantitative statistics | Structural studies resolved human EMC at 3.4 Å overall resolution with ~12 TMs in the membrane region; proteomics identified 5,570 proteins total, 4,446 quantified, 3,188 membrane-associated, 971 with transmembrane annotation, and 36 EMC-dependent membrane proteins versus 171 EMC-independent ones. Recent topology work estimated ~250 new putative EMC-sensitive multipass substrates. In bipolar-cell cKO mice, Emc3 deletion affected ~75% of BCs, reduced Emc3 expression by ~40-45%, lowered scotopic b-waves by ~50%, photopic b-waves by ~30%, OPs to ~51-62% of control, caused ~50% loss of PKCα+ rod bipolar cells, and reduced INL thickness to ~55% of control at 12 months (pqac-00000015, pqac-00000023, pqac-00000024, pqac-00000017, pqac-00000034, pqac-00000035) | Pleiner et al. 2020; Tian et al. 2019; Wu et al. 2024; Zhu et al. 2020 | https://doi.org/10.1126/science.abb5008 ; https://doi.org/10.1016/j.celrep.2019.08.006 ; https://doi.org/10.1038/s41594-023-01120-6 ; https://doi.org/10.1371/journal.pone.0238435 |


*Table: This table summarizes verified identity, mechanism, localization, key recent advances, representative clients, phenotypic relevance, and quantitative evidence for human EMC3 (UniProt Q9P0I2). It is useful as a compact evidence-based reference for functional annotation.*