EMC4

UniProt ID: Q5J8M3
Organism: Homo sapiens
Review Status: COMPLETE
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Gene Description

EMC4 (ER membrane protein complex subunit 4; also TMEM85) is a small (~183-residue, ~20 kDa) polytopic ER membrane protein and a constitutive structural subunit of the ER membrane protein complex (EMC), a conserved nine- to ten-subunit transmembrane-domain insertase and membrane-protein chaperone of the endoplasmic reticulum. Cryo-EM structures resolve EMC4 with a cytoplasmic N-terminus, transmembrane segments, and a lumenal C-terminus, packing against the other membrane subunits to help form and stabilize the complex. EMC4 is not part of the catalytic insertase core, which is formed by the EMC3 and EMC6 subunits that build the membrane-embedded hydrophilic substrate vestibule; instead EMC4 is an accessory/scaffold subunit. As part of the EMC it contributes to the energy-independent insertion of newly synthesized membrane proteins into the ER membrane, with a preference for transmembrane domains that are weakly hydrophobic or carry destabilizing charged or aromatic residues. The complex mediates post-translational insertion of tail-anchored proteins and cotranslational insertion and N-exo topogenesis of multipass membrane proteins, including transporters and G protein-coupled receptors, in cooperation with the Sec61 translocon. EMC4 is broadly expressed and resides in the ER membrane.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0072546 EMC complex
IBA
GO_REF:0000033
ACCEPT
Summary: Phylogenetic (PAN-GO) assignment of EMC complex membership across the EMC4 family, matching direct experimental and structural evidence. Core structural identity of EMC4.
Reason: EMC complex membership is the core cellular-component identity of EMC4 and is supported by IDA, cryo-EM structures, and the conserved EMC4 family.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
Component of the ER membrane protein complex (EMC).
GO:0005789 endoplasmic reticulum membrane
IEA
GO_REF:0000044
ACCEPT
Summary: Electronic transfer of the ER membrane subcellular location from UniProt; the correct and core compartment for the multipass ER membrane subunit EMC4.
Reason: Correct core location; redundant with experimental EXP/IDA evidence.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0005515 protein binding
IPI
PMID:31695625
Interaction Between ITM2B and GLUT9 Links Urate Transport to...
KEEP AS NON CORE
Summary: IntAct interaction of EMC4/TMEM85 with the multipass urate transporter GLUT9/SLC2A9 (Q9NRM0). In the functional assay TMEM85 (unlike ITM2B) did not affect GLUT9-mediated urate uptake; the interaction most plausibly reflects EMC4 engaging GLUT9 as an EMC client (consistent with the EMC's transporter-client preference). Bare protein binding is uninformative.
Reason: Plausible EMC-client (transporter) interaction, but bare protein binding is uninformative per curation guidelines and the functional assay showed no role of TMEM85 in urate transport itself; not elevated to core.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
Q5J8M3; Q9NRM0-1: SLC2A9
GO:0005515 protein binding
IPI
PMID:33845483
Multilevel proteomics reveals host perturbations by SARS-CoV...
KEEP AS NON CORE
Summary: High-throughput SARS-CoV-2/SARS-CoV proteomics interactome capturing EMC4 with the viral replicase polyprotein (P0DTD1, rep). Bare protein binding is uninformative and the partner is a viral xenobiotic protein unrelated to EMC4's core function.
Reason: Real virus-host interactome capture but bare protein binding is uninformative; the viral partner does not inform EMC4's core ER insertase scaffolding role.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
Q5J8M3; PRO_0000449624 [P0DTD1]: rep
GO:0005515 protein binding
IPI
PMID:34232536
Interactomes of SARS-CoV-2 and human coronaviruses reveal ho...
KEEP AS NON CORE
Summary: Comparative coronavirus interactome screen capturing the EMC4-viral replicase (P0DTD1, rep) interaction. Bare protein binding is uninformative and the partner is a viral protein.
Reason: Real virus-host interactome capture; bare protein binding is uninformative and the viral partner is not part of EMC4's core function.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
Q5J8M3; PRO_0000449624 [P0DTD1]: rep
GO:0005515 protein binding
IPI
PMID:36217030
A comprehensive SARS-CoV-2-human protein-protein interactome...
KEEP AS NON CORE
Summary: Comprehensive SARS-CoV-2-human interactome capturing the EMC4-viral replicase (P0DTD1, rep) interaction. Bare protein binding is uninformative and the partner is a viral protein.
Reason: Real virus-host interactome capture; bare protein binding is uninformative and the viral partner does not reflect EMC4's core insertase scaffolding role.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
Q5J8M3; PRO_0000449624 [P0DTD1]: rep
GO:0005789 endoplasmic reticulum membrane
NAS
PMID:29242231
The ER membrane protein complex is a transmembrane domain in...
ACCEPT
Summary: ComplexPortal NAS annotation of ER membrane localization for the EMC, consistent with the experimental evidence and core compartment of EMC4.
Reason: Correct core location; consistent with EXP/IDA evidence.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0045050 protein insertion into ER membrane by stop-transfer membrane-anchor sequence
IDA
PMID:29242231
The ER membrane protein complex is a transmembrane domain in...
ACCEPT
Summary: The EMC inserts transmembrane domains, including stop-transfer membrane-anchor sequences of multipass clients; EMC4 is a constitutive subunit. Core complex-level process.
Reason: Core EMC-mediated process; the EMC is a demonstrated transmembrane-domain insertase and EMC4 is a structural subunit.
Supporting Evidence:
PMID:29242231
transmembrane domain insertase
GO:0071816 tail-anchored membrane protein insertion into ER membrane
IDA
PMID:29242231
The ER membrane protein complex is a transmembrane domain in...
ACCEPT
Summary: The EMC mediates post-translational insertion of tail-anchored proteins with moderately hydrophobic TMDs, demonstrated directly in this study; EMC4 is a constitutive subunit. Core complex-level process.
Reason: Core EMC-mediated process; directly demonstrated for the complex.
Supporting Evidence:
PMID:29242231
tail-anchored membrane proteins with moderately hydrophobic transmembrane
GO:0072546 EMC complex
IPI
PMID:32439656
Structural basis for membrane insertion by the human ER memb...
ACCEPT
Summary: ComplexPortal IPI assignment of EMC complex membership based on the cryo-EM structure of the human EMC, which resolves EMC4 as a membrane subunit. Core structural identity.
Reason: Structurally demonstrated core EMC membership.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
Component of the ER membrane protein complex (EMC).
GO:0005789 endoplasmic reticulum membrane
EXP
PMID:22119785
Defining human ERAD networks through an integrative mapping ...
ACCEPT
Summary: Experimental ER membrane localization from the foundational ERAD-network mapping study that first identified the EMC (TMEM85). Core compartment.
Reason: Experimentally supported core location.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0032977 membrane insertase activity
IMP
PMID:29809151
The ER membrane protein complex interacts cotranslationally ...
ACCEPT
Summary: IMP evidence (cotranslational multipass biogenesis study) that the EMC has membrane insertase activity, to which EMC4 contributes as a structural subunit. The contributes_to qualifier is appropriate because EMC4 is not catalytic (the vestibule is EMC3/EMC6).
Reason: Complex-level MF correctly qualified contributes_to; EMC4 supports the insertase activity of the EMC as an accessory membrane subunit but is not itself catalytic.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
enables the energy-independent insertion into endoplasmic
GO:0032977 membrane insertase activity
IMP
PMID:30415835
EMC Is Required to Initiate Accurate Membrane Protein Topoge...
ACCEPT
Summary: IMP evidence (topogenesis study) supporting the EMC's membrane insertase activity, to which EMC4 contributes as a structural subunit. contributes_to correctly reflects that EMC4 is non-catalytic.
Reason: Complex-level MF correctly qualified contributes_to; EMC4 supports the insertase activity of the EMC.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
enables the energy-independent insertion into endoplasmic
GO:0045050 protein insertion into ER membrane by stop-transfer membrane-anchor sequence
IMP
PMID:29809151
The ER membrane protein complex interacts cotranslationally ...
ACCEPT
Summary: The EMC is required for cotranslational insertion of multipass proteins in which stop-transfer membrane-anchor sequences become membrane-spanning helices; EMC4 is a constitutive subunit. Core EMC process.
Reason: Core EMC-mediated process; supported by IMP of EMC subunits.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
stop-transfer membrane-anchor sequences become ER membrane spanning
GO:0005789 endoplasmic reticulum membrane
IDA
PMID:32439656
Structural basis for membrane insertion by the human ER memb...
ACCEPT
Summary: Direct (cryo-EM structural) evidence placing EMC4 in the ER membrane as a membrane subunit of the EMC. Core compartment.
Reason: Experimentally supported core location.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0045050 protein insertion into ER membrane by stop-transfer membrane-anchor sequence
IMP
PMID:30415835
EMC Is Required to Initiate Accurate Membrane Protein Topoge...
ACCEPT
Summary: IMP evidence (topogenesis study) that the EMC inserts stop-transfer membrane-anchor sequences and sets the N-exo topology of multipass clients such as GPCRs; EMC4 is part of the insertase complex. Core EMC process.
Reason: Core EMC-mediated process.
Supporting Evidence:
PMID:30415835
G protein-coupled receptors
GO:0016020 membrane
IDA
PMID:22119785
Defining human ERAD networks through an integrative mapping ...
KEEP AS NON CORE
Summary: Direct generic membrane localization from the EMC-discovery study; a parent of the specific ER membrane term.
Reason: Correct but generic; the ER membrane term captures the informative localization.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0072546 EMC complex
IDA
PMID:22119785
Defining human ERAD networks through an integrative mapping ...
ACCEPT
Summary: Direct experimental identification of EMC4/TMEM85 in the EMC by the foundational ERAD-network mapping study. Core structural identity.
Reason: Core EMC membership; directly demonstrated.
Supporting Evidence:
file:human/EMC4/EMC4-uniprot.txt
Component of the ER membrane protein complex (EMC).

Core Functions

Constitutive accessory/structural membrane subunit of the ER membrane protein complex (EMC); packs against the other membrane subunits to help form and stabilize the complex and contributes to its energy-independent membrane insertase activity, while the catalytic vestibule is formed by EMC3 and EMC6.

Molecular Function:
membrane insertase activity
In Complex:
EMC complex
Supporting Evidence:
  • file:human/EMC4/EMC4-uniprot.txt
    Component of the ER membrane protein complex (EMC).
  • file:human/EMC4/EMC4-uniprot.txt
    enables the energy-independent insertion into endoplasmic
  • PMID:37199759
    EMC4 is resolved as a three-TMD subunit that, with EMC7/EMC10, partially encloses the hydrophilic insertase vestibule and contacts substrates at the client-facing surface.
  • PMID:38517390
    EMC4 forms an ordered three-TMH bundle adjacent to the EMC3/EMC6 core, constituting a sidewall of the hydrophilic vestibule.

As part of the EMC, contributes to post-translational insertion of tail-anchored proteins and cotranslational insertion and N-exo topogenesis of multipass membrane proteins (including transporters and GPCRs) at the ER membrane.

Supporting Evidence:
  • file:human/EMC4/EMC4-uniprot.txt
    post-translational insertion of tail-anchored/TA proteins in
  • PMID:37196677
    EMC4 participates in the client-engaging cytoplasmic chaperone module and lumenal EMC1/EMC4/EMC7/EMC10 subassembly during assembly of the multipass CaV1.2 channel.

References

The architecture of EMC reveals a path for membrane protein insertion.
Annotation inferences using phylogenetic trees
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
Defining human ERAD networks through an integrative mapping strategy.
  • Affinity-MS ERAD-network mapping that first identified the EMC (including TMEM85/EMC4) in human cells and localized it to the ER membrane.
The ER membrane protein complex is a transmembrane domain insertase.
  • EMC is a transmembrane domain insertase that post-translationally inserts tail-anchored membrane proteins with moderately hydrophobic TMDs.
The ER membrane protein complex interacts cotranslationally to enable biogenesis of multipass membrane proteins.
  • The EMC engages multipass membrane protein clients cotranslationally, with a particular enrichment for transporters, to enable their biogenesis.
EMC Is Required to Initiate Accurate Membrane Protein Topogenesis.
  • The EMC sets the N-exo topology of the first TMD of GPCRs and other multipass proteins, initiating accurate topogenesis in cooperation with Sec61.
Interaction Between ITM2B and GLUT9 Links Urate Transport to Neurodegenerative Disorders.
  • TMEM85/EMC4 interacts with GLUT9/SLC2A9, but ITM2B (not TMEM85) inhibited GLUT9-mediated urate uptake.
Structural basis for membrane insertion by the human ER membrane protein complex.
  • Cryo-EM structure of the human EMC; substrate insertion occurs via an enclosed hydrophilic vestibule formed by EMC3 and EMC6, with EMC4 resolved as a membrane subunit of the complex.
Multilevel proteomics reveals host perturbations by SARS-CoV-2 and SARS-CoV.
Interactomes of SARS-CoV-2 and human coronaviruses reveal host factors potentially affecting pathogenesis.
A comprehensive SARS-CoV-2-human protein-protein interactome reveals COVID-19 pathobiology and potential host therapeutic targets.
A selectivity filter in the ER membrane protein complex limits protein misinsertion at the ER.
  • Improved cryo-EM model of human EMC assigns three transmembrane domains to EMC4; EMC4/EMC7/EMC10 TMDs partially enclose the hydrophilic insertase vestibule, and substrate photocrosslinking/disulfide crosslinking detects contacts with EMC4 as well as EMC3.
EMC chaperone-Ca(V) structure reveals an ionΒ channel assembly intermediate.
  • Cryo-EM of an EMC-bound CaV1.2 assembly intermediate shows the EMC acts as a holdase/chaperone during voltage-gated calcium channel assembly; EMC4 participates in the client-engaging cytoplasmic chaperone module and in a lumenal EMC1/EMC4/EMC7/EMC10 subassembly.
Structural insights into human EMC and its interaction with VDAC.
  • Cryo-EM structures of human EMC in apo and VDAC-bound states; EMC4 forms an ordered three-TMH bundle adjacent to the EMC3/EMC6 core that constitutes a sidewall of the hydrophilic vestibule, and the EMC engages VDAC at mitochondria-ER contact sites.
Lipid scrambling is a general feature of protein insertases.
  • Reconstitution and coarse-grained MD indicate lipid scrambling is a general feature of protein insertases, with EMC scrambling activity localized to EMC3 and EMC4; scrambling occurs in the same hydrophilic channel used for protein insertion.
Dual roles for the ER membrane protein complex in flavivirus infection: viral entry and protein biogenesis.
  • EMC4 is a proviral host factor for dengue, yellow fever, and Zika viruses, acting both at an early entry/uncoating step and in biogenesis of viral multipass membrane proteins; EMC4 knockout/knockdown strongly reduces infectivity and viral titers.
The ER Membrane Protein Complex Promotes Biogenesis of Dengue and Zika Virus Non-structural Multi-pass Transmembrane Proteins to Support Infection.
  • The EMC promotes biogenesis of flavivirus non-structural multipass transmembrane proteins (e.g., NS4B); EMC associates with these viral clients, consistent with a direct role in viral membrane-protein biogenesis.
Selective EMC subunits act as molecular tethers of intracellular organelles exploited during viral entry.
  • EMC4 and EMC7 promote late endosome-to-ER targeting of polyomavirus SV40 during entry; EMC4 engages Rab7 and syntaxin18 and is proposed to act as a tether stabilizing late endosome-ER contacts, with EMC4-FLAG rescue supporting specificity.
file:human/EMC4/EMC4-uniprot.txt
UniProt entry Q5J8M3 (EMC4_HUMAN), ER membrane protein complex subunit 4
  • Small polytopic ER membrane accessory subunit of the EMC (TMEM85); structural/scaffold subunit, not part of the EMC3/EMC6 catalytic vestibule; interacts with the EMC client transporter GLUT9/SLC2A9.

Suggested Questions for Experts

Q: What specific structural role does EMC4 play in EMC assembly and stability, and does loss of EMC4 selectively impair insertion of particular client classes (e.g. multipass transporters)?

Q: Does the EMC4-GLUT9 interaction represent a productive client-engagement event during GLUT9 biogenesis, and is GLUT9 surface expression EMC4-dependent?

Suggested Experiments

Experiment: Knock out EMC4 in human cells and perform quantitative membrane proteomics with rescue to define the EMC4-dependent client repertoire and distinguish it from clients tolerant of EMC4 loss.

Experiment: Test EMC4 dependence of GLUT9 and other candidate transporter clients by measuring their folding, ER export and plasma-membrane levels in EMC4-depleted versus rescued cells.

Deep Research

Falcon

(EMC4-deep-research-falcon.md)
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 62 citations 2 artifacts 2026-06-12T01:40:22.867189

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research report: Human EMC4 (UniProt Q5J8M3; gene EMC4; synonyms TMEM85, PIG17) β€” functional annotation

0) Target verification (mandatory)

The literature and database evidence retrieved here consistently match the UniProt-provided identity: human EMC4 = β€œER membrane protein complex subunit 4”, encoded by EMC4 (Ensembl ENSG00000128463), and functioning as a subunit of the ER membrane protein complex (EMC). This aligns with UniProt Q5J8M3 (ER membrane protein complex subunit 4; TMEM85/ PIG17) and with Open Targets target metadata. (OpenTargets Search: -EMC4)


1) Key concepts and current understanding

1.1 What is EMC and what does it do?

The endoplasmic reticulum membrane protein complex (EMC) is an ER-localized, multi-subunit membrane protein biogenesis factor that acts as a co- and post-translational insertase for certain transmembrane helices (TMDs). Structural and biochemical evidence supports a model in which EMC provides a hydrophilic vestibule within the bilayer to reduce the energetic barrier for insertion of challenging TMDs (e.g., weakly hydrophobic tail-anchors), while also supporting later steps of folding/assembly for complex multipass clients. (pleiner2020structuralbasisfor pages 7-11, pleiner2020structuralbasisfor pages 1-3, odonnell2020thearchitectureof pages 1-2)

A central mechanistic concept is that EMC contains intramembrane cavities/surfaces that engage substrate TMDs and provide an β€œenergy-independent” insertion route without nucleotide-binding domains. (odonnell2020thearchitectureof pages 1-2, odonnell2020thearchitectureof pages 2-4)

1.2 What is EMC4 specifically?

EMC4 is a membrane-embedded EMC subunit that (i) contributes to the architecture enclosing the insertase vestibule and (ii) participates in EMC’s client-facing surfaces.

A major update from 2023 is that improved cryo-EM maps unambiguously assign three transmembrane domains (TMDs) in human EMC4; EMC4, together with the single TMDs of EMC7 and EMC10, helps enclose the insertase vestibule. (pleiner2023aselectivityfilter pages 4-6)

Mechanistically, EMC4 is not merely a passive scaffold: EMC4 is found at the client-interaction environment (vestibule side) and can be crosslinked to substrates, consistent with a direct role in substrate handling. (pleiner2023aselectivityfilter pages 2-4, pleiner2023aselectivityfilter pages 19-23)


2) Structure, localization, and mechanistic role of EMC4

2.1 Subcellular localization

EMC (including EMC4) is localized to the endoplasmic reticulum membrane. This is directly supported by multiple human EMC structural studies performed on purified/reconstituted complexes and by functional assays in cells where EMC supports ER membrane insertion events. (pleiner2020structuralbasisfor pages 7-11, pleiner2020structuralbasisfor pages 1-3, odonnell2020thearchitectureof pages 1-2)

2.2 EMC architecture and where EMC4 sits

High-resolution cryo-EM defines the EMC as a tripartite assembly with cytosolic, membrane, and lumenal domains. In one foundational structure, the human EMC map was reported at ~3.4 Γ… overall resolution, with a prominent intramembrane hydrophilic vestibule formed by the conserved insertase core (EMC3/EMC6). (pleiner2020structuralbasisfor pages 1-3)

EMC4 is positioned adjacent to this insertase core and contributes to the vestibule enclosure:
* Pleiner et al. (J Cell Biol, 2023-05) show that the hydrophilic vestibule is partially enclosed by dynamic TMDs from EMC4/7/10, and that three EMC4 TMDs can be assigned in an improved reconstruction. (pleiner2023aselectivityfilter pages 4-6)
* Li et al. (Aging, 2024-03) likewise describe EMC4 as an ordered three-TMH bundle adjacent to EMC3/EMC6 that forms part of the sidewall of the hydrophilic vestibule, reinforcing EMC4’s direct role in shaping the substrate-binding/insertion environment. (li2024structuralinsightsinto pages 1-3)

2.3 Insertase mechanism and the EMC4 contribution

The EMC insertase is centered on the EMC3/EMC6 module that provides a hydrophilic vestibule for insertion. (pleiner2020structuralbasisfor pages 1-3, pleiner2023aselectivityfilter pages 4-6)

EMC4 contributes in three experimentally supported ways:
1. Vestibule enclosure and geometry: the vestibule is β€œpartially enclosed” by EMC4/7/10 TMDs; EMC4 loss can impair incorporation of EMC7 and EMC10 into EMC, consistent with EMC4’s architectural role. (pleiner2023aselectivityfilter pages 4-6)
2. Direct substrate proximity: in substrate mapping, site-specific photocrosslinking and disulfide crosslinking detect substrate contacts not only with EMC3 but also with EMC4, consistent with EMC4 forming part of the client-facing surface of the vestibule. (pleiner2023aselectivityfilter pages 2-4, pleiner2023aselectivityfilter pages 19-23)
3. Functional requirement for tail-anchored biogenesis: EMC4 is required for biogenesis/insertion of the tail-anchored substrate squalene synthase (SQS/FDFT1) in the Pleiner et al. reporter systems. (pleiner2023aselectivityfilter pages 19-23, pleiner2023aselectivityfilter pages 23-26)

2.4 EMC selectivity filter (2023 mechanistic development)

Pleiner et al. (J Cell Biol, 2023-05) propose that the EMC hydrophilic vestibule acts as a selectivity filter that limits misinsertion/mislocalization by using charge-based discrimination.

Key points supported by experiments:
* The vestibule is positively charged and can repel substrates with positively charged soluble domains, helping enforce correct topology (β€œpositive-inside” considerations) and preventing inappropriate ER insertion of mitochondrial tail-anchored proteins. (pleiner2023aselectivityfilter pages 6-8, pleiner2023aselectivityfilter pages 8-10)
* This work includes a sequence-scale analysis of 709 human GPCR sequences, and shows that even one added positive charge to an SQS reporter C-terminus can markedly reduce ER integration in cells and in vitro. (pleiner2023aselectivityfilter pages 6-8)

EMC4’s role here is primarily structural (enclosing the vestibule and contributing substrate-facing surfaces), whereas the most explicitly tested selectivity residues in text are on EMC3 (e.g., R31/R180). (pleiner2023aselectivityfilter pages 4-6, pleiner2023aselectivityfilter pages 8-10)


3) Recent developments (prioritizing 2023–2024)

3.1 2023: EMC4 resolved as a 3-TMD vestibule-enclosing subunit and mapped in substrate crosslinking

The 2023 J Cell Biol study improved assignment of EMC4 TMDs and provides multiple crosslinking modalities showing substrates can contact EMC4 at the vestibule side. (pleiner2023aselectivityfilter pages 4-6, pleiner2023aselectivityfilter pages 2-4, pleiner2023aselectivityfilter pages 19-23)

3.2 2023: EMC acts as a chaperone/holdase during CaV channel assembly; EMC4 participates

Chen et al. (Nature, 2023-05-) determined cryo-EM structures of an EMC-bound assembly intermediate for voltage-gated calcium channel CaV1.2, concluding that EMC functions as a holdase/chaperone during assembly. The EMC–CaV1.2(Ξ”C)–CaVΞ²3 complex is reported as ~0.6 MDa and solved at 3.4 Γ… and 3.3 Γ… overall. (chen2023emcchaperone–cavstructure pages 3-4, chen2023emcchaperone–cavstructure pages 1-3)

EMC4 is part of EMC’s client-engaging architecture in this system:
* The cytoplasmic chaperone module that engages CaV includes EMC2, EMC3, EMC4, EMC5 and EMC8. (chen2023emcchaperone–cavstructure pages 3-4)
* A lumenal subassembly comprising EMC1/EMC4/EMC7/EMC10 is implicated in supporting a transmembrane docking region during channel assembly. (chen2023emcchaperone–cavstructure pages 11-13)

3.3 2024: EMC4 and ER–mitochondria contact-site biology (VDAC interaction)

Li et al. (Aging, 2024-03) report cryo-EM structures of human EMC and a VDAC-bound state, suggesting EMC can engage VDAC proteins at mitochondria–ER contact sites and that a β€œgating plug” inside the vestibule changes conformation between apo and VDAC-bound conditions. In that analysis, EMC4 forms part of the ordered three-TMH bundle shaping the vestibule sidewall. (li2024structuralinsightsinto pages 1-3)

3.4 2024: Lipid scrambling hypothesisβ€”Emc4 implicated among insertases

Li et al. (PNAS, 2024-04) propose that lipid scrambling is a general feature of protein insertases, and report coarse-grained MD evidence localizing EMC scrambling activity specifically to Emc3 and Emc4. They tested >150 proteins/complexes in silico and quantified lipid scrambling with an angular criterion (>125Β° for upper-leaflet lipids; <55Β° for lower-leaflet lipids). (li2024lipidscramblingis pages 3-5, li2024lipidscramblingis pages 7-8)

While this is not yet a definitive demonstration of human EMC4 scramblase activity in cells, it is a mechanistically coherent proposal because the same hydrophilic pathway used for protein insertion could allow lipid flip-flop. (li2024lipidscramblingis pages 3-5)


4) Biological processes, pathways, and client/substrate classes (functional annotation)

4.1 Primary function (best-supported)

The best-supported β€œprimary” function for EMC4 is as a structural and mechanistic subunit of the EMC insertase/chaperone machinery that promotes membrane protein biogenesis in the ER by:
* shaping/enclosing the hydrophilic vestibule used for insertion, and
* participating in client engagement surfaces (crosslinking evidence), and
* enabling downstream folding/assembly steps for complex multipass clients (e.g., CaV channels). (pleiner2023aselectivityfilter pages 4-6, pleiner2023aselectivityfilter pages 2-4, chen2023emcchaperone–cavstructure pages 3-4)

EMC4 is not an enzyme with a known catalytic reaction; rather, it is a membrane biogenesis factor contributing to a proteinaceous insertion/chaperone environment.

4.2 Substrate/client examples and classes

Across the retrieved sources, EMC clients include:
* Tail-anchored proteins with weakly hydrophobic TMDs, including SQS/FDFT1 (a canonical EMC-dependent TA in multiple studies). (pleiner2020structuralbasisfor pages 7-11, pleiner2023aselectivityfilter pages 19-23)
* Multipass membrane proteins, enriched for transporters in proteomic datasets, and including ion channels. (shurtleff2018theermembrane pages 8-10, chen2023emcchaperone–cavstructure pages 3-4)
* Voltage-gated calcium channels: EMC binds an assembly intermediate and supports maturation/functional expression. (chen2023emcchaperone–cavstructure pages 3-4)

Quantitative proteomics in mammalian cells reported 11 proteins decreased β‰₯2-fold upon both EMC2 and EMC4 depletion (10/11 with at least one TMD), consistent with an effect on a subset of membrane proteins rather than global translation changes. (shurtleff2018theermembrane pages 8-10)


5) Real-world applications and implementations

5.1 Antiviral biology: EMC4 as a host dependency factor

Multiple viruses exploit ER biogenesis machinery. EMC4 is experimentally validated as a proviral host factor for several viruses:

Flaviviruses (dengue, yellow fever, Zika)
* EMC4 knockout/targeting reduces infectivity and virus production, with effects reported as ~5–20-fold reductions in infectivity (YFV imaging assays) and up to 3 log10 reduced extracellular YFV titers at 33.5 h post infection; for DENV2/DENV4, virus output fell below detection in EMC4 KO lines in the described assays. (barrows2019dualrolesfor pages 3-5)
* EMC4 depletion in a ZIKV replicon context reduced replicon RNA by ~54–55% and EMC4 protein levels by 73% or 94% (two siRNAs), with downstream reductions in multiple viral proteins. (barrows2019dualrolesfor pages 9-10)
* Biochemically, EMC4 is used for co-immunoprecipitation assays in which EMC associates with flavivirus non-structural multipass proteins such as NS4B, consistent with a direct role in viral membrane-protein biogenesis. (lin2019theermembrane pages 13-14)

Polyomavirus SV40 entry
EMC4 and EMC7 promote late endosome-to-ER targeting of SV40 during entry. EMC4 engages Rab7 (late endosome) and syntaxin18 (ER fusion machinery) and is proposed to act as a tether stabilizing LE–ER contacts that facilitate viral transport; EMC4-FLAG rescue experiments support specificity. (bagchi2020selectiveemcsubunits pages 1-2)

These findings create a plausible translational directionβ€”targeting host insertion/trafficking dependenciesβ€”although the retrieved evidence does not yet provide a clinically validated EMC4-specific inhibitor or trial.

5.2 Membrane-protein proteostasis engineering

Structural mechanistic definition of EMC (including EMC4’s vestibule enclosure and CaV chaperone role) informs biotechnological strategies aimed at improving expression/assembly of difficult multipass proteins (e.g., channels and GPCRs) in cell systems by modulating EMC function. (pleiner2023aselectivityfilter pages 4-6, chen2023emcchaperone–cavstructure pages 3-4)


6) Expert opinions / authoritative synthesis

A recurring expert view is that EMC is built around a deeply conserved insertase core and has additional roles in folding/assembly that extend beyond insertion alone. Structural and mechanistic studies emphasize that distinct EMC regions contribute to different client classes (tail-anchored vs multipass), consistent with EMC being a multifunctional membrane biogenesis machine. (millervedam2020structuralandmechanistic pages 7-10, pleiner2020structuralbasisfor pages 7-11, millervedam2020structuralandmechanistic pages 18-21)

In this context, EMC4 is best interpreted as a β€œperipheral-but-mechanistically-relevant” subunit: depletion of EMC4 may leave other EMC subunits largely stable (suggesting it is not the sole assembly scaffold), yet it is required for specific biogenesis functions and contributes to the vestibule/client interface. (shurtleff2018theermembrane pages 8-10, pleiner2023aselectivityfilter pages 4-6)


7) Disease associations and human genetics (current evidence limits)

Direct, well-established monogenic human diseases caused by EMC4 variants were not identified in the retrieved full-text evidence. However, aggregated evidence in Open Targets links EMC4 to multiple disease categories (including neurodegenerative diseases and dengue disease) with modest scores and evidence size = 5 for each shown association; this should be interpreted as hypothesis-generating and often driven by functional genomics screens rather than causal human genetics. (OpenTargets Search: -EMC4)


8) Visual evidence supporting EMC4’s structural role

The following retrieved figure crops from Pleiner et al. (J Cell Biol, 2023) visually support the claim that EMC4’s 3 TMDs enclose the EMC3/6 insertase core hydrophilic vestibule and that EMC10 contributes additional enclosure density. (pleiner2023aselectivityfilter media 2fbee94e, pleiner2023aselectivityfilter media bf0f9cf4, pleiner2023aselectivityfilter media ac5195ae)


Evidence map (compact summary)

Topic Key findings Key quantitative/statistical details Key sources with publication year and URL Citation IDs
Identity / localization Human EMC4 is ER membrane protein complex subunit 4, encoded by EMC4 (ENSG00000128463), matching UniProt Q5J8M3. EMC is an ER-localized multi-subunit insertase/chaperone complex required for membrane protein biogenesis. Human EMC described as 9-subunit; complex dimensions reported at ~200 Γ— 70 Γ— 100 Γ… in one cryo-EM study. Open Targets EMC4 target entry; Pleiner et al., 2020, Science, https://doi.org/10.1126/science.abb5008; O'Donnell et al., 2020, eLife, https://doi.org/10.7554/elife.57887 (OpenTargets Search: -EMC4, pleiner2020structuralbasisfor pages 1-3, odonnell2020thearchitectureof pages 1-2)
Structure / topology of EMC4 EMC4 is a membrane subunit adjacent to the EMC3/EMC6 insertase core. Improved human cryo-EM maps assigned 3 EMC4 transmembrane helices, and EMC4 also contributes a C-terminal Ξ²-strand that completes an EMC1 membrane-proximal Ξ²-propeller, indicating structural roles in both the membrane and lumenal domains. 3 TMDs assigned to EMC4 in 2023 human structure; vestibule partly enclosed by 5 dynamic TMDs from EMC4/7/10. Pleiner et al., 2023, J Cell Biol, https://doi.org/10.1083/jcb.202212007; Li et al., 2024, Aging (Albany NY), https://doi.org/10.18632/aging.205660; Pleiner et al., 2020, Science, https://doi.org/10.1126/science.abb5008 (pleiner2023aselectivityfilter pages 4-6, pleiner2023aselectivityfilter pages 2-4, pleiner2023aselectivityfilter pages 19-23, li2024structuralinsightsinto pages 1-3, pleiner2020structuralbasisfor pages 1-3)
Insertase mechanism EMC acts as a co- and post-translational insertase for transmembrane helices, especially weakly hydrophobic tail-anchored TMDs and some multipass membrane proteins. Mechanistically, EMC3/EMC6 form a hydrophilic vestibule that lowers the energetic barrier to membrane insertion, while EMC4 helps shape/enclose this insertion environment. Cryo-EM resolutions reported at 3.4 Γ… overall for human EMC; vestibule includes conserved positive charges and a methionine-rich capture loop; membrane proteins comprise ~20–25% of eukaryotic/human genes according to review/background. Pleiner et al., 2020, Science, https://doi.org/10.1126/science.abb5008; O'Donnell et al., 2020, eLife, https://doi.org/10.7554/elife.57887; Bai et al., 2020, Nature, https://doi.org/10.1038/s41586-020-2389-3; Hegde, 2022, Annu Rev Biochem, https://doi.org/10.1146/annurev-biochem-032620-104553 (pleiner2020structuralbasisfor pages 7-11, pleiner2020structuralbasisfor pages 1-3, bai2020structureofthe pages 1-2, odonnell2020thearchitectureof pages 1-2)
EMC4 role in vestibule architecture / substrate contacts EMC4 partially encloses only the hydrophilic vestibule side of EMC, and substrate photocrosslinking/disulfide-crosslinking showed contacts with EMC4 as well as EMC3. EMC4 loss also impairs incorporation of EMC7 and EMC10, indicating EMC4 helps assemble the vestibule-enclosing module. Disulfide formation interpreted at ~3–5 Γ… proximity; crosslinking detected for EMC3 and EMC4; complete EMC4 loss impaired EMC7/EMC10 assembly. Pleiner et al., 2023, J Cell Biol, https://doi.org/10.1083/jcb.202212007 (pleiner2023aselectivityfilter pages 4-6, pleiner2023aselectivityfilter pages 2-4, pleiner2023aselectivityfilter pages 19-23)
Selectivity filter / topology control EMC contains a positively charged hydrophilic vestibule that acts as a selectivity filter, repelling substrates with positively charged soluble domains and limiting misinsertion of mitochondrial TA proteins while helping enforce correct topology of multipass substrates. EMC4 contributes the sidewall/enclosure of this vestibule rather than the key charged residues themselves. Analysis included 709 human GPCR sequences; even a single added positive charge to an SQS reporter strongly reduced ER insertion; electrostatic potential mapped from βˆ’3 to +3 kT/e; EMC3 R31/R180 mutants altered selectivity. Pleiner et al., 2023, J Cell Biol, https://doi.org/10.1083/jcb.202212007 (pleiner2023aselectivityfilter pages 4-6, pleiner2023aselectivityfilter pages 6-8, pleiner2023aselectivityfilter pages 8-10)
Chaperone / assembly role for multipass proteins Beyond insertase activity, EMC also functions as a holdase/chaperone for complex multipass clients. In the CaV1.2 assembly intermediate, EMC4 participates in the EMC client-binding/chaperone architecture and in the lumenal EMC1/4/7/10 module that supports a transmembrane docking site during channel assembly. EMC–CaV1.2(Ξ”C)–CaVΞ²3 complex mass ~0.6 MDa; cryo-EM maps at 3.4 Γ… and 3.3 Γ…; Cyto dock ~1,500 Γ…Β² with EMC8 site 962 Γ…Β² and EMC2 site 550 Γ…Β². Chen et al., 2023, Nature, https://doi.org/10.1038/s41586-023-06175-5; Miller-Vedam et al., 2020, eLife, https://doi.org/10.1101/2020.09.02.280008 (chen2023emcchaperone–cavstructure pages 11-13, chen2023emcchaperone–cavstructure pages 3-4, chen2023emcchaperone–cavstructure pages 1-3, millervedam2020structuralandmechanistic pages 18-21)
Peripheral versus structural-essential subunit behavior EMC4 is not as globally assembly-critical as EMC2, but it is not merely dispensable: EMC4 depletion leaves many other EMC subunits stable, yet phenocopies client defects and contributes directly to insertion/chaperone functions. Reviews and knockdown studies therefore place EMC4 among more peripheral subunits with specific mechanistic importance. In one proteomic study, 11 proteins decreased β‰₯2-fold in both EMC2- and EMC4-depleted cells, and 10/11 had at least one TMD; EMC4 knockdown had no effect on abundance of other EMC members in that dataset. Shurtleff et al., 2018, eLife, https://doi.org/10.7554/elife.37018; Chitwood & Hegde, 2019, Trends Cell Biol, https://doi.org/10.1016/j.tcb.2019.01.007 (shurtleff2018theermembrane pages 8-10, chitwood2019theroleof pages 2-4)
Client/substrate classes and pathways EMC/EMC4 support biogenesis of tail-anchored proteins (e.g., SQS/FDFT1), sterol-related enzymes, GPCRs, ion channels, and diverse multipass transporters/secretory membrane proteins. EMC-dependent biology therefore connects EMC4 to membrane protein proteostasis, sterol/cholesterol homeostasis, and ER quality-control pathways. Yeast TMT proteomics identified 38 likely EMC clients; mammalian depletion studies found 11 proteins reduced β‰₯2-fold in both EMC2 and EMC4 knockdown backgrounds. Bai et al., 2020, Nature, https://doi.org/10.1038/s41586-020-2389-3; Volkmar et al., 2019, J Cell Sci, https://doi.org/10.1242/jcs.223453; Shurtleff et al., 2018, eLife, https://doi.org/10.7554/elife.37018 (bai2020structureofthe pages 1-2, shurtleff2018theermembrane pages 8-10)
Lipid scrambling hypothesis Recent computational/biophysical work suggests lipid scrambling may be a general property of insertases and localizes EMC scrambling activity specifically to Emc3 and Emc4 in silico. This supports a model in which EMC4 helps create a hydrophilic pathway used for both protein insertion and lipid flip-flop. >150 proteins/complexes tested in silico; scrambling criterion used lipid angle >125Β° (upper leaflet) or <55Β° (lower leaflet); BSA back-extraction assay typically reduced NBD fluorescence by ~50% (practically 35–45%). Li et al., 2024, PNAS, https://doi.org/10.1073/pnas.2319476121 (li2024lipidscramblingis pages 3-5, li2024lipidscramblingis pages 7-8, li2024lipidscramblingis pages 2-3)
Viral host-factor role: flaviviruses EMC4 is a validated proviral host factor for dengue, yellow fever, and Zika viruses. EMC4 supports infection at least at two stages: an early step at or before uncoating and a later step in viral membrane-protein biogenesis, including NS4B-associated processes. EMC4-targeting sgRNAs reduced YFV infectivity ~5–20-fold; EMC4 KO caused up to 3 log10 lower YFV titers by 33.5 hpi; DENV2/DENV4 production fell below detection; anti-EMC4 siRNAs reduced ZIKV replicon RNA by ~54–55% with 73% or 94% EMC4 knockdown. Barrows et al., 2019, Sci Rep, https://doi.org/10.1038/s41598-019-45910-9; Lin et al., 2019, Cell Reports, https://doi.org/10.1016/j.celrep.2019.04.051; Verhaegen & Vermeire, 2024, npj Viruses, https://doi.org/10.1038/s44298-024-00031-7 (barrows2019dualrolesfor pages 3-5, lin2019theermembrane pages 13-14, barrows2019dualrolesfor pages 1-2, barrows2019dualrolesfor pages 9-10)
Viral host-factor role: SV40 / organelle tethering EMC4 also has a more selective EMC-independent or EMC-submodule-like role in SV40 entry, where EMC4 and EMC7 promote late endosome-to-ER transport. EMC4 engages Rab7 and syntaxin18 and was proposed to act as a molecular tether stabilizing LE–ER contacts needed for viral trafficking. EMC4 knockdown blocked SV40 infection; siRNA-resistant EMC4-FLAG fully rescued infection in the reported assays. Bagchi et al., 2020, Nat Commun, https://doi.org/10.1038/s41467-020-14967-w (bagchi2020selectiveemcsubunits pages 1-2)
Disease / phenotype associations Direct monogenic human disease attribution for EMC4 itself remains limited in the retrieved evidence, but EMC4 is linked through EMC biology to neurodegeneration-related screening signals, lysosomal storage disease, Alzheimer disease, Parkinson disease, and dengue disease in Open Targets evidence aggregation. Expert reviews emphasize broader EMC involvement in membrane-protein folding diseases and cholesterol-homeostasis phenotypes rather than EMC4-specific clinical syndromes. Open Targets evidence sizes shown as 5 for the listed EMC4 disease associations; no clinical trials were retrieved. Open Targets EMC4 associations; Hegde, 2022, Annu Rev Biochem, https://doi.org/10.1146/annurev-biochem-032620-104553; Volkmar et al., 2019, J Cell Sci, https://doi.org/10.1242/jcs.223453 (OpenTargets Search: -EMC4, chitwood2019theroleof pages 2-4)

Table: This table summarizes the main experimentally supported roles of human EMC4 within the ER membrane protein complex, including structure, mechanism, client classes, and disease-relevant phenotypes. It is useful as a compact evidence map linking EMC4-specific findings to broader EMC biology.


Key source list (URLs; publication dates)

  • Pleiner T. et al. A selectivity filter in the ER membrane protein complex limits protein misinsertion at the ER. J Cell Biol (published 2023-05). https://doi.org/10.1083/jcb.202212007 (pleiner2023aselectivityfilter pages 4-6, pleiner2023aselectivityfilter pages 2-4, pleiner2023aselectivityfilter pages 6-8)
  • Chen Z. et al. EMC chaperone–CaV structure reveals an ion channel assembly intermediate. Nature 619 (published 2023-05). https://doi.org/10.1038/s41586-023-06175-5 (chen2023emcchaperone–cavstructure pages 3-4, chen2023emcchaperone–cavstructure pages 1-3)
  • Li M. et al. Structural insights into human EMC and its interaction with VDAC. Aging (Albany NY) (published 2024-03). https://doi.org/10.18632/aging.205660 (li2024structuralinsightsinto pages 1-3)
  • Li D. et al. Lipid scrambling is a general feature of protein insertases. PNAS (published 2024-04). https://doi.org/10.1073/pnas.2319476121 (li2024lipidscramblingis pages 3-5, li2024lipidscramblingis pages 7-8)
  • Pleiner T. et al. Structural basis for membrane insertion by the human ER membrane protein complex. Science (published 2020-07). https://doi.org/10.1126/science.abb5008 (pleiner2020structuralbasisfor pages 1-3)
  • O’Donnell J.P. et al. The architecture of EMC reveals a path for membrane protein insertion. eLife (published 2020-05). https://doi.org/10.7554/elife.57887 (odonnell2020thearchitectureof pages 1-2)
  • Barrows N.J. et al. Dual roles for the ER membrane protein complex in flavivirus infection: viral entry and protein biogenesis. Sci Rep (published 2019-07). https://doi.org/10.1038/s41598-019-45910-9 (barrows2019dualrolesfor pages 3-5, barrows2019dualrolesfor pages 9-10)
  • Bagchi P. et al. Selective EMC subunits act as molecular tethers of intracellular organelles exploited during viral entry. Nat Commun (published 2020-02). https://doi.org/10.1038/s41467-020-14967-w (bagchi2020selectiveemcsubunits pages 1-2)

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  26. (pleiner2023aselectivityfilter media bf0f9cf4): Tino Pleiner, Masami Hazu, Giovani Pinton Tomaleri, Vy N. Nguyen, Kurt Januszyk, and Rebecca M. Voorhees. A selectivity filter in the er membrane protein complex limits protein misinsertion at the er. The Journal of Cell Biology, May 2023. URL: https://doi.org/10.1083/jcb.202212007, doi:10.1083/jcb.202212007. This article has 28 citations.

  27. (pleiner2023aselectivityfilter media ac5195ae): Tino Pleiner, Masami Hazu, Giovani Pinton Tomaleri, Vy N. Nguyen, Kurt Januszyk, and Rebecca M. Voorhees. A selectivity filter in the er membrane protein complex limits protein misinsertion at the er. The Journal of Cell Biology, May 2023. URL: https://doi.org/10.1083/jcb.202212007, doi:10.1083/jcb.202212007. This article has 28 citations.

  28. (bai2020structureofthe pages 1-2): Lin Bai, Qinglong You, Xiang Feng, Amanda Kovach, and Huilin Li. Structure of the er membrane complex, a transmembrane-domain insertase. Jun 2020. URL: https://doi.org/10.1038/s41586-020-2389-3, doi:10.1038/s41586-020-2389-3. This article has 164 citations and is from a highest quality peer-reviewed journal.

  29. (chitwood2019theroleof pages 2-4): Patrick J. Chitwood and Ramanujan S. Hegde. The role of emc during membrane protein biogenesis. Trends in cell biology, 29 5:371-384, May 2019. URL: https://doi.org/10.1016/j.tcb.2019.01.007, doi:10.1016/j.tcb.2019.01.007. This article has 97 citations and is from a domain leading peer-reviewed journal.

  30. (li2024lipidscramblingis pages 2-3): Dazhi Li, Cristian Rocha-Roa, Matthew A. Schilling, Karin M. Reinisch, and Stefano Vanni. Lipid scrambling is a general feature of protein insertases. Proceedings of the National Academy of Sciences of the United States of America, Apr 2024. URL: https://doi.org/10.1073/pnas.2319476121, doi:10.1073/pnas.2319476121. This article has 70 citations and is from a highest quality peer-reviewed journal.

  31. (barrows2019dualrolesfor pages 1-2): Nicholas J. Barrows, Yesseinia Anglero-Rodriguez, Byungil Kim, Sharon F. Jamison, Caroline Le Sommer, Charles E. McGee, James L. Pearson, George Dimopoulos, Manuel Ascano, Shelton S. Bradrick, and Mariano A. Garcia-Blanco. Dual roles for the er membrane protein complex in flavivirus infection: viral entry and protein biogenesis. Scientific Reports, Jul 2019. URL: https://doi.org/10.1038/s41598-019-45910-9, doi:10.1038/s41598-019-45910-9. This article has 62 citations and is from a peer-reviewed journal.

Artifacts

Citations

  1. pleiner2023aselectivityfilter pages 4-6
  2. pleiner2020structuralbasisfor pages 1-3
  3. li2024structuralinsightsinto pages 1-3
  4. pleiner2023aselectivityfilter pages 6-8
  5. li2024lipidscramblingis pages 3-5
  6. shurtleff2018theermembrane pages 8-10
  7. barrows2019dualrolesfor pages 3-5
  8. barrows2019dualrolesfor pages 9-10
  9. lin2019theermembrane pages 13-14
  10. bagchi2020selectiveemcsubunits pages 1-2
  11. odonnell2020thearchitectureof pages 1-2
  12. pleiner2020structuralbasisfor pages 7-11
  13. odonnell2020thearchitectureof pages 2-4
  14. pleiner2023aselectivityfilter pages 2-4
  15. pleiner2023aselectivityfilter pages 19-23
  16. pleiner2023aselectivityfilter pages 23-26
  17. pleiner2023aselectivityfilter pages 8-10
  18. li2024lipidscramblingis pages 7-8
  19. millervedam2020structuralandmechanistic pages 7-10
  20. millervedam2020structuralandmechanistic pages 18-21
  21. bai2020structureofthe pages 1-2
  22. chitwood2019theroleof pages 2-4
  23. li2024lipidscramblingis pages 2-3
  24. barrows2019dualrolesfor pages 1-2
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πŸ“š Additional Documentation

Notes

(EMC4-notes.md)

EMC4 (TMEM85) review notes

UniProt: Q5J8M3 (EMC4_HUMAN). 183 aa. Synonyms TMEM85, PIG17, HSPC184. Gene on chr15.

Identity / overview

  • EMC4 is a small (~20 kDa) accessory transmembrane subunit of the ER membrane protein complex (EMC), the conserved 9-10 subunit ER insertase. It is NOT the catalytic insertase core (that is EMC3 + EMC6).
  • Topology (from structures): cytoplasmic N-terminus (2-66), three TMs (67-87, 99-120, 128-148) and a lumenal C-terminus, or possibly single-pass. [file:human/EMC4/EMC4-uniprot.txt "TRANSMEM 67..87"]
  • 8 cryo-EM structures (PDB 6Z3W, 7ADO, 7ADP, 8EOI, 8J0N, 8J0O, 8S9S, 9C7V) all resolve EMC4 (chain D) as part of the EMC. Membership is structurally unambiguous.

Function (EMC complex membership)

  • EMC mediates energy-independent insertion of newly synthesized membrane proteins into the ER membrane. [file:human/EMC4/EMC4-uniprot.txt "Part of the endoplasmic reticulum membrane protein complex"]
  • EMC = TA (tail-anchored) protein post-translational insertase. PMID:29242231; preferentially accommodates weakly hydrophobic TMDs.
  • EMC engages multipass membrane proteins co-translationally, enriched for transporters. PMID:29809151
  • EMC sets topology of multipass proteins (e.g. GPCRs) via co-translational N-exo insertion of the first TMD. PMID:30415835
  • The catalytic vestibule is formed by EMC3 and EMC6 β€” NOT EMC4. PMID:32439656
  • EMC4 is therefore a structural/scaffold subunit; its catalytic-activity annotations are correctly given with the contributes_to qualifier (it contributes to complex insertase activity, not standalone).

Complex membership / localization

  • Identified in mEMC (mammalian EMC) as TMEM85 by Christianson 2011. PMID:22119785
  • SUBCELLULAR LOCATION: ER membrane, multi-pass membrane protein. [file:human/EMC4/EMC4-uniprot.txt "SUBCELLULAR LOCATION: Endoplasmic reticulum membrane"]

Protein interactions (IPI / bare protein binding)

  • SLC2A9 / GLUT9 (Q9NRM0-1, Q9NRM0-2): TMEM85 was tested as a GLUT9 interactor; in the functional assay TMEM85 did NOT affect urate transport (ITM2B did). PMID:31695625. This is likely EMC4 acting as the EMC subunit engaging the multipass transporter client GLUT9 (consistent with EMC's transporter-client preference), but recorded only as bare protein binding.
  • SARS-CoV-2 rep/nsp interactions (P0DTD1 PRO_0000449624): from three large viral-host interactome screens (PMID:33845483, PMID:34232536, PMID:36217030), all abstract-only in cache. IntAct INTERACTION block of UniProt lists "Q5J8M3; PRO_0000449624 [P0DTD1]: rep". These are high-throughput viral-host PPIs; bare protein binding, non-core.

Curation decisions summary

  • CORE: EMC complex membership (GO:0072546 part_of), ER membrane (GO:0005789), TA insertion (GO:0071816 involved_in), stop-transfer multipass insertion (GO:0045050 involved_in).
  • membrane insertase activity (GO:0032977) with contributes_to: ACCEPT (complex-level catalytic contribution, scaffold framing), not standalone core MF for EMC4.
  • All bare protein binding (GO:0005515 IPI): KEEP_AS_NON_CORE.
  • GO:0016020 membrane: redundant/generic vs ER membrane -> KEEP_AS_NON_CORE.
  • apoptotic process (GO:0006915, IEA KW): from old yeast/human TMEM85 H2O2-cell-death observation PMID:18586032; this is an indirect/pleiotropic downstream effect, MARK_AS_OVER_ANNOTATED (note: this term is a UniProtKB-KW IEA and appears in the DR GO block but is not in goa.tsv, so not in existing_annotations list).

Verification pass (2026-06-11)

  • All 18 PENDING annotations reviewed and filled; status COMPLETE.
  • Verbatim substrings confirmed in cache/uniprot: uniprot "Component of the ER membrane protein complex (EMC).", "SUBCELLULAR LOCATION: Endoplasmic reticulum membrane", "Q5J8M3; Q9NRM0-1: SLC2A9", "Q5J8M3; PRO_0000449624 [P0DTD1]: rep", "enables the energy-independent insertion into endoplasmic", "post-translational insertion of tail-anchored/TA proteins in", "stop-transfer membrane-anchor sequences become ER membrane spanning"; PMID:29242231 "transmembrane domain insertase" / "tail-anchored membrane proteins with moderately hydrophobic transmembrane"; PMID:30415835 "G protein-coupled receptors".
  • IPI partners: PMID:31695625 -> GLUT9/SLC2A9 (multipass transporter client; KEEP_AS_NON_CORE); PMID:33845483/34232536/36217030 -> SARS-CoV-2 replicase rep (P0DTD1, viral; KEEP_AS_NON_CORE).
  • EMC4 is a non-catalytic accessory membrane subunit; GO:0032977 insertase activity carries contributes_to and is ACCEPTed at complex level. CORE = EMC complex membership + ER membrane + TA/stop-transfer insertion processes. No REMOVE/MODIFY/UNDECIDED.

Falcon deep-research findings (incorporated 2026-06)

New EMC4-relevant references verified against PubMed and added to the review (all additive; no action changes):

  • Improved 2023 human EMC cryo-EM resolves three TMDs in EMC4; EMC4/EMC7/EMC10 TMDs partially enclose the EMC3/EMC6 hydrophilic insertase vestibule, and substrate photocrosslinking/disulfide crosslinking detects contacts with EMC4 (not only EMC3). EMC4 loss also impairs EMC7/EMC10 incorporation. PMID:37199759
  • The EMC acts as a holdase/chaperone during assembly of the multipass voltage-gated Ca channel CaV1.2; EMC4 is part of the client-engaging cytoplasmic chaperone module and of a lumenal EMC1/EMC4/EMC7/EMC10 subassembly. PMID:37196677
  • Independent 2024 human EMC cryo-EM (apo + VDAC-bound) describes EMC4 as an ordered three-TMH bundle adjacent to EMC3/EMC6 forming a sidewall of the vestibule; EMC engages VDAC at mitochondria-ER contact sites. PMID:38517390
  • Reconstitution + MD propose lipid scrambling as a general insertase feature, localized to EMC3 and EMC4, in the same hydrophilic channel used for protein insertion (hypothesis-generating; not yet shown for human EMC4 in cells). PMID:38621120
  • EMC4 is a proviral host factor for flaviviruses (dengue, yellow fever, Zika), acting at an early entry/uncoating step and in viral multipass protein biogenesis. PMID:31273220; the EMC also supports flavivirus NS4B/non-structural multipass protein biogenesis PMID:31067454.
  • EMC4 (with EMC7) acts as a molecular tether of late endosome-ER contacts during SV40 entry, engaging Rab7 and syntaxin18 β€” a role partly distinct from the bulk EMC insertase. PMID:32111841
  • Note: these antiviral/tether roles are informative but recorded as non-core context; the core EMC4 identity remains EMC complex membership + ER-membrane localization + contribution to the insertase/TA + multipass insertion processes.

Pn Notes

(EMC4-pn-notes.md)

EMC4 PN Consistency Notes

  • Generated: 2026-06-18
  • Project: PROTEOSTASIS
  • Scope: PN consistency rereview against local AIGR review and available deep-research artifacts
  • UniProt: Q5J8M3
  • AIGR review status: COMPLETE
  • Review batch: proteostasis-batch-2026-06-11
  • Batch change status: added

Source Files Checked

Deep Research Files

AIGR Review Snapshot

  • Description: EMC4 (ER membrane protein complex subunit 4; also TMEM85) is a small (~183-residue, ~20 kDa) polytopic ER membrane protein and a constitutive structural subunit of the ER membrane protein complex (EMC), a conserved nine- to ten-subunit transmembrane-domain insertase and membrane-protein chaperone of the endoplasmic reticulum. Cryo-EM structures resolve EMC4 with a cytoplasmic N-terminus, transmembrane segments, and a lumenal C-terminus, packing against the other membrane subunits to help form and stabilize the complex. EMC4 is not part of the catalytic insertase core, which is formed by the EMC3 and EMC6 subunits that build the membrane-embedded hydrophilic substrate vestibule; instead EMC4 is an accessory/scaffold subunit. As part of the EMC it contributes to the energy-independent insertion of newly synthesized membrane proteins into the ER membrane, with a preference for transmembrane domains that are weakly hydrophobic or carry destabilizing charged or aromatic residues. The complex mediates post-translational insertion of tail-anchored proteins and cotranslational insertion and N-exo topogenesis of multipass membrane proteins, including transporters and G protein-coupled receptors, in cooperation with the Sec61 translocon. EMC4 is broadly expressed and resides in the ER membrane.
  • Existing/core annotation action counts: ACCEPT: 13; KEEP_AS_NON_CORE: 5

PN Consistency Summary

  • Consistency: Strong agreement. EMC4 (TMEM85) is an accessory/structural membrane subunit (three-TMD vestibule sidewall, not catalytic). Deep research, review, and PN annotation concur. Review captures GO:0072546, ER membrane, GO:0032977 (contributes_to, correctly NOT elevated to catalytic), and insertion BPs. No contradictions.
  • PN story / NEW pressure: PN asserts nothing beyond GO coverage. EMC4 has additional distinctive non-core biology in the review (flavivirus host factor PMID:31273220/PMID:31067454; SV40 late-endosome-ER tethering via Rab7/syntaxin18 PMID:32111841; putative EMC3/EMC4 lipid-scramblase PMID:38621120) β€” all correctly kept as context/non-core, none rising to a defensible NEW GO term (scramblase is computational/not demonstrated for human EMC4 in vivo). Conclusion: already captured.
  • Evidence alignment: Excellent overlap on core EMC papers (PMID:22119785, PMID:29242231, PMID:32439656, PMID:30415835, PMID:37199759, PMID:37196677, PMID:38517390). Review adds EMC4-specific functional-genetics references absent from PN. PN cites no row-1 titles; no divergence.
  • Verdict: Consistent; PN adds no NEW pressure; projected group/class terms broader than review (no mapping change warranted).

Full Consistency Review

  • UniProt: Q5J8M3 Β· batch: proteostasis-batch-2026-06-11 Β· review status: COMPLETE (thorough; all annotations adjudicated)
  • PN placement: ER proteostasis | Protein transport | Transmembrane protein import | EMC complex component; PN-node mapping: type=mapped/ok_for_propagation β†’ GO:0072546 EMC complex (already_in_goa_exact); groupβ†’GO:0044743, classβ†’GO:0015031 (new_to_goa); branch=no_mapping.
  • Consistency: Strong agreement. EMC4 (TMEM85) is an accessory/structural membrane subunit (three-TMD vestibule sidewall, not catalytic). Deep research, review, and PN annotation concur. Review captures GO:0072546, ER membrane, GO:0032977 (contributes_to, correctly NOT elevated to catalytic), and insertion BPs. No contradictions.
  • PN story / NEW pressure: PN asserts nothing beyond GO coverage. EMC4 has additional distinctive non-core biology in the review (flavivirus host factor PMID:31273220/PMID:31067454; SV40 late-endosome-ER tethering via Rab7/syntaxin18 PMID:32111841; putative EMC3/EMC4 lipid-scramblase PMID:38621120) β€” all correctly kept as context/non-core, none rising to a defensible NEW GO term (scramblase is computational/not demonstrated for human EMC4 in vivo). Conclusion: already captured.
  • Mapping strategy: EMC4 does not change the node. typeβ†’GO:0072546 exact/correct. Projected group/class terms (GO:0044743, GO:0015031) are broader than the review's specific insertion terms β€” broader-ancestor pattern (cf. TOMM20/HSPA8/RAB7A). The tethering/scramblase roles are EMC4-specific but are not part of the PN "transmembrane protein import" node and should not alter it. No mapping change warranted.
  • Evidence alignment: Excellent overlap on core EMC papers (PMID:22119785, PMID:29242231, PMID:32439656, PMID:30415835, PMID:37199759, PMID:37196677, PMID:38517390). Review adds EMC4-specific functional-genetics references absent from PN. PN cites no row-1 titles; no divergence.
  • Verdict: Consistent; PN adds no NEW pressure; projected group/class terms broader than review (no mapping change warranted).

PN Dossier Context

  • review_batch: proteostasis-batch-2026-06-11
  • review_yaml: genes/human/EMC4/EMC4-ai-review.yaml
  • PN workbook rows: 1

PN row 1: ER proteostasis | Protein transport | Transmembrane protein import | EMC complex component

  • UniProt: Q5J8M3
  • In branches: ER
  • PN-node mapping records (path + ancestors):
    • [type] ER proteostasis|Protein transport|Transmembrane protein import|EMC complex component
      status=mapped scope=ok_for_propagation_to_go GO=[GO:0072546 EMC complex]
      rationale: This PN type denotes ER membrane protein complex components. The GO EMC complex cellular-component term is the direct target.
    • [group] ER proteostasis|Protein transport|Transmembrane protein import
      status=mapped scope=ok_for_propagation_to_go GO=[GO:0044743 protein transmembrane import into intracellular organelle]
      rationale: This PN group covers ER transmembrane-protein insertion/import systems such as EMC- and PAT-related pathways. The local GO cache does not expose an ER-specific matching term, so the broader intracellular-organelle transmembrane-import process is the best supported propagation target.
    • [class] ER proteostasis|Protein transport
      status=mapped scope=ok_for_propagation_to_go GO=[GO:0015031 protein transport]
      rationale: The PN ER Protein transport class groups ER-targeting and ER-insertion pathways. GO protein transport is the appropriate propagation target, while the source class remains ER-specific and broader than any single GO transport subtype.
    • [branch] ER proteostasis
      status=no_mapping scope= GO=[]
      rationale: Reviewed as a top-level PN branch. This is a systems/taxonomy umbrella, not a direct GO assertion; narrower child curations carry any propagating GO mappings.

Projected GO annotations (3)

  • GO:0015031 protein transport | scope=ok_for_propagation_to_go | goa_status=new_to_goa | from=ER proteostasis|Protein transport
  • GO:0044743 protein transmembrane import into intracellular organelle | scope=ok_for_propagation_to_go | goa_status=new_to_goa | from=ER proteostasis|Protein transport|Transmembrane protein import
  • GO:0072546 EMC complex | scope=ok_for_propagation_to_go | goa_status=already_in_goa_exact | from=ER proteostasis|Protein transport|Transmembrane protein import|EMC complex component

Note

This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.

πŸ“„ View Raw YAML

id: Q5J8M3
gene_symbol: EMC4
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: EMC4 (ER membrane protein complex subunit 4; also TMEM85) is a small (~183-residue, ~20 kDa) polytopic ER membrane protein and a constitutive structural subunit of the ER membrane protein complex (EMC), a conserved nine- to ten-subunit transmembrane-domain insertase and membrane-protein chaperone of the endoplasmic reticulum. Cryo-EM structures resolve EMC4 with a cytoplasmic N-terminus, transmembrane segments, and a lumenal C-terminus, packing against the other membrane subunits to help form and stabilize the complex. EMC4 is not part of the catalytic insertase core, which is formed by the EMC3 and EMC6 subunits that build the membrane-embedded hydrophilic substrate vestibule; instead EMC4 is an accessory/scaffold subunit. As part of the EMC it contributes to the energy-independent insertion of newly synthesized membrane proteins into the ER membrane, with a preference for transmembrane domains that are weakly hydrophobic or carry destabilizing charged or aromatic residues. The complex mediates post-translational insertion of tail-anchored proteins and cotranslational insertion and N-exo topogenesis of multipass membrane proteins, including transporters and G protein-coupled receptors, in cooperation with the Sec61 translocon. EMC4 is broadly expressed and resides in the ER membrane.
alternative_products:
- name: 1 (TMEM85v1)
  id: Q5J8M3-1
- name: 2 (TMEM85v2)
  id: Q5J8M3-2
  sequence_note: VSP_020798, VSP_020799
- name: '3'
  id: Q5J8M3-3
  sequence_note: VSP_037374, VSP_037375
existing_annotations:
- term:
    id: GO:0072546
    label: EMC complex
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: part_of
  review:
    summary: Phylogenetic (PAN-GO) assignment of EMC complex membership across the EMC4 family, matching direct experimental and structural evidence. Core structural identity of EMC4.
    action: ACCEPT
    reason: EMC complex membership is the core cellular-component identity of EMC4 and is supported by IDA, cryo-EM structures, and the conserved EMC4 family.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: Component of the ER membrane protein complex (EMC).
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Electronic transfer of the ER membrane subcellular location from UniProt; the correct and core compartment for the multipass ER membrane subunit EMC4.
    action: ACCEPT
    reason: Correct core location; redundant with experimental EXP/IDA evidence.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:31695625
  qualifier: enables
  review:
    summary: IntAct interaction of EMC4/TMEM85 with the multipass urate transporter GLUT9/SLC2A9 (Q9NRM0). In the functional assay TMEM85 (unlike ITM2B) did not affect GLUT9-mediated urate uptake; the interaction most plausibly reflects EMC4 engaging GLUT9 as an EMC client (consistent with the EMC's transporter-client preference). Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Plausible EMC-client (transporter) interaction, but bare protein binding is uninformative per curation guidelines and the functional assay showed no role of TMEM85 in urate transport itself; not elevated to core.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: 'Q5J8M3; Q9NRM0-1: SLC2A9'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33845483
  qualifier: enables
  review:
    summary: High-throughput SARS-CoV-2/SARS-CoV proteomics interactome capturing EMC4 with the viral replicase polyprotein (P0DTD1, rep). Bare protein binding is uninformative and the partner is a viral xenobiotic protein unrelated to EMC4's core function.
    action: KEEP_AS_NON_CORE
    reason: Real virus-host interactome capture but bare protein binding is uninformative; the viral partner does not inform EMC4's core ER insertase scaffolding role.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: 'Q5J8M3; PRO_0000449624 [P0DTD1]: rep'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:34232536
  qualifier: enables
  review:
    summary: Comparative coronavirus interactome screen capturing the EMC4-viral replicase (P0DTD1, rep) interaction. Bare protein binding is uninformative and the partner is a viral protein.
    action: KEEP_AS_NON_CORE
    reason: Real virus-host interactome capture; bare protein binding is uninformative and the viral partner is not part of EMC4's core function.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: 'Q5J8M3; PRO_0000449624 [P0DTD1]: rep'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:36217030
  qualifier: enables
  review:
    summary: Comprehensive SARS-CoV-2-human interactome capturing the EMC4-viral replicase (P0DTD1, rep) interaction. Bare protein binding is uninformative and the partner is a viral protein.
    action: KEEP_AS_NON_CORE
    reason: Real virus-host interactome capture; bare protein binding is uninformative and the viral partner does not reflect EMC4's core insertase scaffolding role.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: 'Q5J8M3; PRO_0000449624 [P0DTD1]: rep'
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: NAS
  original_reference_id: PMID:29242231
  qualifier: located_in
  review:
    summary: ComplexPortal NAS annotation of ER membrane localization for the EMC, consistent with the experimental evidence and core compartment of EMC4.
    action: ACCEPT
    reason: Correct core location; consistent with EXP/IDA evidence.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0045050
    label: protein insertion into ER membrane by stop-transfer membrane-anchor sequence
  evidence_type: IDA
  original_reference_id: PMID:29242231
  qualifier: involved_in
  review:
    summary: The EMC inserts transmembrane domains, including stop-transfer membrane-anchor sequences of multipass clients; EMC4 is a constitutive subunit. Core complex-level process.
    action: ACCEPT
    reason: Core EMC-mediated process; the EMC is a demonstrated transmembrane-domain insertase and EMC4 is a structural subunit.
    supported_by:
    - reference_id: PMID:29242231
      supporting_text: transmembrane domain insertase
- term:
    id: GO:0071816
    label: tail-anchored membrane protein insertion into ER membrane
  evidence_type: IDA
  original_reference_id: PMID:29242231
  qualifier: involved_in
  review:
    summary: The EMC mediates post-translational insertion of tail-anchored proteins with moderately hydrophobic TMDs, demonstrated directly in this study; EMC4 is a constitutive subunit. Core complex-level process.
    action: ACCEPT
    reason: Core EMC-mediated process; directly demonstrated for the complex.
    supported_by:
    - reference_id: PMID:29242231
      supporting_text: tail-anchored membrane proteins with moderately hydrophobic transmembrane
- term:
    id: GO:0072546
    label: EMC complex
  evidence_type: IPI
  original_reference_id: PMID:32439656
  qualifier: part_of
  review:
    summary: ComplexPortal IPI assignment of EMC complex membership based on the cryo-EM structure of the human EMC, which resolves EMC4 as a membrane subunit. Core structural identity.
    action: ACCEPT
    reason: Structurally demonstrated core EMC membership.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: Component of the ER membrane protein complex (EMC).
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: EXP
  original_reference_id: PMID:22119785
  qualifier: located_in
  review:
    summary: Experimental ER membrane localization from the foundational ERAD-network mapping study that first identified the EMC (TMEM85). Core compartment.
    action: ACCEPT
    reason: Experimentally supported core location.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0032977
    label: membrane insertase activity
  evidence_type: IMP
  original_reference_id: PMID:29809151
  qualifier: contributes_to
  review:
    summary: IMP evidence (cotranslational multipass biogenesis study) that the EMC has membrane insertase activity, to which EMC4 contributes as a structural subunit. The contributes_to qualifier is appropriate because EMC4 is not catalytic (the vestibule is EMC3/EMC6).
    action: ACCEPT
    reason: Complex-level MF correctly qualified contributes_to; EMC4 supports the insertase activity of the EMC as an accessory membrane subunit but is not itself catalytic.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: enables the energy-independent insertion into endoplasmic
- term:
    id: GO:0032977
    label: membrane insertase activity
  evidence_type: IMP
  original_reference_id: PMID:30415835
  qualifier: contributes_to
  review:
    summary: IMP evidence (topogenesis study) supporting the EMC's membrane insertase activity, to which EMC4 contributes as a structural subunit. contributes_to correctly reflects that EMC4 is non-catalytic.
    action: ACCEPT
    reason: Complex-level MF correctly qualified contributes_to; EMC4 supports the insertase activity of the EMC.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: enables the energy-independent insertion into endoplasmic
- term:
    id: GO:0045050
    label: protein insertion into ER membrane by stop-transfer membrane-anchor sequence
  evidence_type: IMP
  original_reference_id: PMID:29809151
  qualifier: involved_in
  review:
    summary: The EMC is required for cotranslational insertion of multipass proteins in which stop-transfer membrane-anchor sequences become membrane-spanning helices; EMC4 is a constitutive subunit. Core EMC process.
    action: ACCEPT
    reason: Core EMC-mediated process; supported by IMP of EMC subunits.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: stop-transfer membrane-anchor sequences become ER membrane spanning
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IDA
  original_reference_id: PMID:32439656
  qualifier: located_in
  review:
    summary: Direct (cryo-EM structural) evidence placing EMC4 in the ER membrane as a membrane subunit of the EMC. Core compartment.
    action: ACCEPT
    reason: Experimentally supported core location.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0045050
    label: protein insertion into ER membrane by stop-transfer membrane-anchor sequence
  evidence_type: IMP
  original_reference_id: PMID:30415835
  qualifier: involved_in
  review:
    summary: IMP evidence (topogenesis study) that the EMC inserts stop-transfer membrane-anchor sequences and sets the N-exo topology of multipass clients such as GPCRs; EMC4 is part of the insertase complex. Core EMC process.
    action: ACCEPT
    reason: Core EMC-mediated process.
    supported_by:
    - reference_id: PMID:30415835
      supporting_text: G protein-coupled receptors
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IDA
  original_reference_id: PMID:22119785
  qualifier: located_in
  review:
    summary: Direct generic membrane localization from the EMC-discovery study; a parent of the specific ER membrane term.
    action: KEEP_AS_NON_CORE
    reason: Correct but generic; the ER membrane term captures the informative localization.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0072546
    label: EMC complex
  evidence_type: IDA
  original_reference_id: PMID:22119785
  qualifier: part_of
  review:
    summary: Direct experimental identification of EMC4/TMEM85 in the EMC by the foundational ERAD-network mapping study. Core structural identity.
    action: ACCEPT
    reason: Core EMC membership; directly demonstrated.
    supported_by:
    - reference_id: file:human/EMC4/EMC4-uniprot.txt
      supporting_text: Component of the ER membrane protein complex (EMC).
core_functions:
- description: Constitutive accessory/structural membrane subunit of the ER membrane protein complex (EMC); packs against the other membrane subunits to help form and stabilize the complex and contributes to its energy-independent membrane insertase activity, while the catalytic vestibule is formed by EMC3 and EMC6.
  molecular_function:
    id: GO:0032977
    label: membrane insertase activity
  in_complex:
    id: GO:0072546
    label: EMC complex
  locations:
  - id: GO:0005789
    label: endoplasmic reticulum membrane
  supported_by:
  - reference_id: file:human/EMC4/EMC4-uniprot.txt
    supporting_text: Component of the ER membrane protein complex (EMC).
  - reference_id: file:human/EMC4/EMC4-uniprot.txt
    supporting_text: enables the energy-independent insertion into endoplasmic
  - reference_id: PMID:37199759
    supporting_text: EMC4 is resolved as a three-TMD subunit that, with EMC7/EMC10, partially encloses the hydrophilic insertase vestibule and contacts substrates at the client-facing surface.
    full_text_unavailable: true
  - reference_id: PMID:38517390
    supporting_text: EMC4 forms an ordered three-TMH bundle adjacent to the EMC3/EMC6 core, constituting a sidewall of the hydrophilic vestibule.
    full_text_unavailable: true
- description: As part of the EMC, contributes to post-translational insertion of tail-anchored proteins and cotranslational insertion and N-exo topogenesis of multipass membrane proteins (including transporters and GPCRs) at the ER membrane.
  molecular_function:
    id: GO:0032977
    label: membrane insertase activity
  locations:
  - id: GO:0005789
    label: endoplasmic reticulum membrane
  supported_by:
  - reference_id: file:human/EMC4/EMC4-uniprot.txt
    supporting_text: post-translational insertion of tail-anchored/TA proteins in
  - reference_id: PMID:37196677
    supporting_text: EMC4 participates in the client-engaging cytoplasmic chaperone module and lumenal EMC1/EMC4/EMC7/EMC10 subassembly during assembly of the multipass CaV1.2 channel.
    full_text_unavailable: true
  directly_involved_in:
  - id: GO:0071816
    label: tail-anchored membrane protein insertion into ER membrane
  - id: GO:0045050
    label: protein insertion into ER membrane by stop-transfer membrane-anchor sequence
proposed_new_terms: []
references:
- id: PMID:32459176
  title: The architecture of EMC reveals a path for membrane protein insertion.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: 'O''Donnell et al. 2020 (eLife). Cryo-EM architecture of the human EMC,
      establishing the overall complex organization and subunit topology relevant to
      EMC4 as a constitutive EMC subunit.'
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
  findings: []
- id: PMID:22119785
  title: Defining human ERAD networks through an integrative mapping strategy.
  findings:
  - statement: Affinity-MS ERAD-network mapping that first identified the EMC (including TMEM85/EMC4) in human cells and localized it to the ER membrane.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Foundational identification of the human EMC; source of EMC complex membership and ER membrane localization for EMC4.
- id: PMID:29242231
  title: The ER membrane protein complex is a transmembrane domain insertase.
  findings:
  - statement: EMC is a transmembrane domain insertase that post-translationally inserts tail-anchored membrane proteins with moderately hydrophobic TMDs.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Establishes the insertase function of the EMC; basis for the insertion BP/MF annotations.
- id: PMID:29809151
  title: The ER membrane protein complex interacts cotranslationally to enable biogenesis of multipass membrane proteins.
  findings:
  - statement: The EMC engages multipass membrane protein clients cotranslationally, with a particular enrichment for transporters, to enable their biogenesis.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Cotranslational multipass biogenesis role of the EMC (transporter clients); basis for the IMP MF/BP annotations.
- id: PMID:30415835
  title: EMC Is Required to Initiate Accurate Membrane Protein Topogenesis.
  findings:
  - statement: The EMC sets the N-exo topology of the first TMD of GPCRs and other multipass proteins, initiating accurate topogenesis in cooperation with Sec61.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Topogenesis/orientation role of the EMC; GPCR clients; basis for IMP MF/BP annotations.
- id: PMID:31695625
  title: Interaction Between ITM2B and GLUT9 Links Urate Transport to Neurodegenerative Disorders.
  findings:
  - statement: TMEM85/EMC4 interacts with GLUT9/SLC2A9, but ITM2B (not TMEM85) inhibited GLUT9-mediated urate uptake.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Source of the EMC4-GLUT9 IPI; the GLUT9 interaction most plausibly reflects EMC4 engaging a multipass transporter client, but TMEM85 itself did not affect urate transport.
- id: PMID:32439656
  title: Structural basis for membrane insertion by the human ER membrane protein complex.
  findings:
  - statement: Cryo-EM structure of the human EMC; substrate insertion occurs via an enclosed hydrophilic vestibule formed by EMC3 and EMC6, with EMC4 resolved as a membrane subunit of the complex.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Structural basis for the EMC; confirms EMC4 as a (non-catalytic) membrane subunit. Abstract-only in cache.
- id: PMID:33845483
  title: Multilevel proteomics reveals host perturbations by SARS-CoV-2 and SARS-CoV.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput virus-host proteomics; source of an IPI protein-binding annotation with the viral replicase (P0DTD1).
- id: PMID:34232536
  title: Interactomes of SARS-CoV-2 and human coronaviruses reveal host factors potentially affecting pathogenesis.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Comparative coronavirus interactome; source of an IPI protein-binding annotation with the viral replicase (P0DTD1).
- id: PMID:36217030
  title: A comprehensive SARS-CoV-2-human protein-protein interactome reveals COVID-19 pathobiology and potential host therapeutic targets.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Comprehensive SARS-CoV-2-human interactome; source of an IPI protein-binding annotation with the viral replicase (P0DTD1).
- id: PMID:37199759
  title: A selectivity filter in the ER membrane protein complex limits protein misinsertion at the ER.
  findings:
  - statement: Improved cryo-EM model of human EMC assigns three transmembrane domains to EMC4; EMC4/EMC7/EMC10 TMDs partially enclose the hydrophilic insertase vestibule, and substrate photocrosslinking/disulfide crosslinking detects contacts with EMC4 as well as EMC3.
    reference_section_type: RESULTS
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: PubMed-verified (J Cell Biol 2023). Recent structural/mechanistic study that resolves EMC4 as a three-TMD vestibule-enclosing subunit and places it at the client-facing surface; directly supports EMC4's structural role in the insertase and the membrane insertase activity annotation.
- id: PMID:37196677
  title: 'EMC chaperone-Ca(V) structure reveals an ionΒ channel assembly intermediate.'
  findings:
  - statement: Cryo-EM of an EMC-bound CaV1.2 assembly intermediate shows the EMC acts as a holdase/chaperone during voltage-gated calcium channel assembly; EMC4 participates in the client-engaging cytoplasmic chaperone module and in a lumenal EMC1/EMC4/EMC7/EMC10 subassembly.
    reference_section_type: RESULTS
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: PubMed-verified (Nature 2023). Establishes a holdase/chaperone mode of the EMC for a multipass client and places EMC4 directly in the client-handling architecture; supports EMC4's role in multipass membrane protein biogenesis.
- id: PMID:38517390
  title: Structural insights into human EMC and its interaction with VDAC.
  findings:
  - statement: Cryo-EM structures of human EMC in apo and VDAC-bound states; EMC4 forms an ordered three-TMH bundle adjacent to the EMC3/EMC6 core that constitutes a sidewall of the hydrophilic vestibule, and the EMC engages VDAC at mitochondria-ER contact sites.
    reference_section_type: RESULTS
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: PubMed-verified (Aging 2024). Independent human EMC structure corroborating EMC4 as a three-TMH vestibule sidewall subunit; supports EMC4's ER-membrane structural role.
- id: PMID:38621120
  title: Lipid scrambling is a general feature of protein insertases.
  findings:
  - statement: Reconstitution and coarse-grained MD indicate lipid scrambling is a general feature of protein insertases, with EMC scrambling activity localized to EMC3 and EMC4; scrambling occurs in the same hydrophilic channel used for protein insertion.
    reference_section_type: RESULTS
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (PNAS 2024). Computational/biochemical proposal of an additional lipid-scramblase activity attributed to EMC3/EMC4; hypothesis-generating for a possible EMC4 function beyond protein insertion (not yet demonstrated for human EMC4 in cells).
- id: PMID:31273220
  title: 'Dual roles for the ER membrane protein complex in flavivirus infection: viral entry and protein biogenesis.'
  findings:
  - statement: EMC4 is a proviral host factor for dengue, yellow fever, and Zika viruses, acting both at an early entry/uncoating step and in biogenesis of viral multipass membrane proteins; EMC4 knockout/knockdown strongly reduces infectivity and viral titers.
    reference_section_type: RESULTS
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (Sci Rep 2019). EMC4-specific functional genetics establishing it as a flavivirus host dependency factor, consistent with the EMC's role in viral multipass membrane-protein biogenesis.
- id: PMID:31067454
  title: The ER Membrane Protein Complex Promotes Biogenesis of Dengue and Zika Virus Non-structural Multi-pass Transmembrane Proteins to Support Infection.
  findings:
  - statement: The EMC promotes biogenesis of flavivirus non-structural multipass transmembrane proteins (e.g., NS4B); EMC associates with these viral clients, consistent with a direct role in viral membrane-protein biogenesis.
    reference_section_type: RESULTS
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (Cell Reports 2019). Mechanistic support that the EMC (engaging clients such as NS4B) supports flavivirus multipass protein biogenesis; corroborates EMC4's antiviral host-factor role.
- id: PMID:32111841
  title: Selective EMC subunits act as molecular tethers of intracellular organelles exploited during viral entry.
  findings:
  - statement: EMC4 and EMC7 promote late endosome-to-ER targeting of polyomavirus SV40 during entry; EMC4 engages Rab7 and syntaxin18 and is proposed to act as a tether stabilizing late endosome-ER contacts, with EMC4-FLAG rescue supporting specificity.
    reference_section_type: RESULTS
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (Nat Commun 2020). EMC4-specific role in organelle tethering/viral trafficking, partly distinct from the bulk EMC insertase function; informative non-core context.
- id: file:human/EMC4/EMC4-uniprot.txt
  title: UniProt entry Q5J8M3 (EMC4_HUMAN), ER membrane protein complex subunit 4
  findings:
  - statement: Small polytopic ER membrane accessory subunit of the EMC (TMEM85); structural/scaffold subunit, not part of the EMC3/EMC6 catalytic vestibule; interacts with the EMC client transporter GLUT9/SLC2A9.
    reference_section_type: OTHER
suggested_questions:
- question: What specific structural role does EMC4 play in EMC assembly and stability, and does loss of EMC4 selectively impair insertion of particular client classes (e.g. multipass transporters)?
- question: Does the EMC4-GLUT9 interaction represent a productive client-engagement event during GLUT9 biogenesis, and is GLUT9 surface expression EMC4-dependent?
suggested_experiments:
- description: Knock out EMC4 in human cells and perform quantitative membrane proteomics with rescue to define the EMC4-dependent client repertoire and distinguish it from clients tolerant of EMC4 loss.
- description: Test EMC4 dependence of GLUT9 and other candidate transporter clients by measuring their folding, ER export and plasma-membrane levels in EMC4-depleted versus rescued cells.