UniProt: Q05320 (VGP_EBOZM), 676 aa, taxon NCBITaxon:128952.
Reviewed for the CACAO project: 5 of the 31 GOA rows
are assigned_by: CACAO.
Deep research was unavailable for this review. No deep-research API keys are
configured in this container, so just deep-research was not run and there is no
GP-deep-research-*.md file. The literature below was read directly: the cached
publications/PMID_*.md entries, the PubMed MCP full-text service (used to recover
the Results/Methods of PMID:20202662, which the cached copy omits), and the UniProt
flat file. The GONUTS wiki (gowiki.tamu.edu), which the CACAO project page
recommends for recovering a student's stated evidence, was offline at the time of
review ("temporarily offline for upgrades"), so the CACAO rows were judged from the
papers themselves.
The single GP gene of EBOV yields three products by RNA editing at a run of seven
uridines (position 295 of the mRNA): unedited RNA → sGP (P60170), +1A → full-length
GP (this entry, Q05320), +2A → ssGP (Q9YMG2)
[file:EBOZM/GP/GP-uniprot.txt "The sequence displayed here is the full-length transmembrane
glycoprotein GP, derived from the +1A edited RNA. The unedited RNA
gives rise to the small secreted glycoprotein sGP (AC P60170), the +2A
edited RNA gives rise to the super small secreted glycoprotein ssGP (AC
Q9YMG2)."].
sGP and ssGP are separate UniProt entries, so they are out of scope for this
review (per the CLAUDE.md alternative-ORF/separate-accession rule); only products
that share Q05320 are modelled here.
Within Q05320 the chains are (FT CHAIN): Envelope glycoprotein 33-676
(PRO_0000037485), Shed GP 33-637 (PRO_0000445686), GP1 33-501 (PRO_0000037486),
GP2 502-676 (PRO_0000037487). Signal peptide 1-32; extracellular 33-650;
TM helix 651-671; cytoplasmic tail 672-676 (five residues). Receptor-binding
region 54-201; mucin-like region 305-485 (largely MobiDB-lite disordered);
fusion peptide 524-539; coiled coils 554-595 and 615-634.
These are cleavage products of one accession, so they are recorded as
functional_isoforms of type CLEAVAGE_PRODUCT mapped to the PRO_ chains, not as
separate gene folders.
GP1,2 trimers are the only spike on the virion; GP1 binds, GP2 fuses
[file:EBOZM/GP/GP-uniprot.txt "Trimeric GP1,2 complexes form the
virion surface spikes and mediate the viral entry processes, with GP1
acting as the receptor-binding subunit and GP2 as the membrane fusion
subunit."]. The trimer is disulfide-linked and chalice-shaped
PMID:26917592.
Attachment cofactors are lectins (CD209/DC-SIGN, CLEC4M/DC-SIGNR, CLEC10A) and
integrin alpha-V; the entry receptor proper is NPC1, which GP1 can only engage
after cathepsin B/L remove the glycan cap in the endosome
[file:EBOZM/GP/GP-uniprot.txt "After internalization of the virus
into the endosomes of the host cell, proteolysis of GP1 by two cysteine
proteases, CTSB/cathepsin B and CTSL/cathepsin L removes the glycan cap
and allows GP1 binding to the host entry receptor NPC1"]. NPC1 binding plus Ca2+ and
low pH then trigger the GP2 conformational change that unmasks the fusion peptide
[file:EBOZM/GP/GP-uniprot.txt "NPC1-binding, Ca(2+) and acidic pH
induce a conformational change of GP2, which unmasks its fusion peptide
and permit membranes fusion"].
Internalisation is clathrin-dependent. PMID:20202662 shows that EbGP-pseudotyped
HIV infection is blocked by four independent perturbations of the clathrin pathway
(chlorpromazine, 0.45 M sucrose, dominant-negative Eps15 DIII, clathrin heavy-chain
siRNA) while wild-type HIV and VSVg-pseudotyped HIV are unaffected, and that
chlorpromazine and bafilomycin A1 block replication-competent ZEBOV-GFP
PMID:20202662. Entry is pH-dependent (Baf A1 sensitive), consistent with
fusion from an endosome rather than the plasma membrane.
The GP2 fusion peptide EBO16 (GAAIGLAWIPYFGPAA, residues ~524-539) adopts a
3(10)-helix in membrane-mimetic environments and interacts with
detergent-resistant (raft) membranes, with Trp8/Phe12 required for the structure
PMID:17545161. This is the evidence behind
the three DisProt lipid binding rows; note the assay used SDS micelles and DRM
fractions, i.e. no physiological lipid class is identified.
PMID:11877482 (the source of two CACAO rows) is a focused raft study:
- Transfected Ebola GP partitions into sucrose-gradient raft fractions, and a
palmitoylation-site mutant does not
PMID:11877482.
- Raft association is cholesterol-dependent (MβCD strips GP from the raft fraction)
and the raft-excluded control TrfR stays soluble
PMID:11877482.
- On intact cells GP colocalises with the raft marker GM1 in plasma-membrane patches
(Fig. 2A, confocal)
PMID:11877482.
So the raft row rests on two independent assay types plus a mutant control — unusually
strong for a CC row, and not the "single-assay localization" CACAO failure mode.
The same paper is also the evidence for GP's contribution to budding: GP alone releases
GM1-containing particulate material, GP+VP40 shifts both proteins into the supernatant,
and the released particles are filamentous, spiked, GM1-positive and TrfR-negative
PMID:11877482,
PMID:11877482,
with EM showing release through small plasma-membrane platforms
PMID:11877482. UniProt reads the same data the same way
[file:EBOZM/GP/GP-uniprot.txt "In the cell,
localizes to the plasma membrane lipid rafts, which probably represent the assembly
and budding site."]. VP40 is the budding driver; GP is incorporated and raises release
efficiency, so budding is a real but secondary role.
PMID:21223600 (third CACAO paper) reports that transiently expressed full-length GP
accumulates in the ER next to the nuclear membrane, and that GPΔmucin does not
PMID:21223600,
PMID:21223600.
Caveats worth recording: this is 10 µg plasmid in HEK293T at 24 h, i.e. gross
overexpression of a protein that is itself cytotoxic; the paper found no Golgi
signal, which sits badly with the established furin cleavage of GP in the trans-Golgi
[file:EBOZM/GP/GP-uniprot.txt "The precursor is processed into GP1 and GP2 by host cell furin in the trans
Golgi"]; and the authors themselves note other studies place GP at the plasma membrane
PMID:21223600.
ER residence is nonetheless expected for a signal-peptide-bearing, N-glycosylated type I
membrane protein, so the term is kept as a non-core biosynthetic location.
ADAM17/TACE cleaves at D637, removing the TM anchor and releasing GP1,2-delta
("shed GP") from the cell surface; shed GP is abundant in the blood of infected
animals and soaks up neutralising antibody
PMID:15103332,
PMID:15103332.
Shed GP is not inert: it binds and activates uninfected DCs and macrophages, raising
pro- and anti-inflammatory cytokines and costimulatory molecules, and increases
vascular permeability; sGP does not do this
PMID:25412102. The receptor is TLR4
PMID:30085081.
Two mechanisms are documented, and they are different:
- Cell-autonomous anoikis. Adenovirus-delivered GP in primary human cardiac
microvascular endothelial cells causes loss of adhesion then death; conditioned
medium does not transfer the effect, so GP must be expressed intracellularly
PMID:15051379. Mechanistically this is downstream of GP-mediated
down-modulation of integrins and MHC-I
[file:EBOZM/GP/GP-uniprot.txt "Down-modulates
several integrins including ITGA1, ITGA2, ITGA3, ITGA4, ITGA5, ITGA6,
ITGAV and ITGB1 (PubMed:11112476)."] — UniProt flags the vascular consequence as
Probable.
- Bystander killing of T cells via TLR4. GP binds CD4+ T cells through TLR4 and
kills them without infecting them; the TLR4 inhibitor CLI-095 rescues
PMID:28542576,
PMID:28542576.
Besides the shed-GP antibody decoy, GP antagonises BST2/tetherin to allow virion
release, and down-regulates surface molecules needed for immune surveillance
[file:EBOZM/GP/GP-uniprot.txt "Counteracts the antiviral effect of host BST2/tetherin that restricts
release of progeny virions from infected cells (PubMed:26516900,
PubMed:27707924, PubMed:29669839)."]. These are the claims behind the
tetherin/innate-immune-suppression keyword IEAs.
| Term | Code | PMID | Action | Note |
|---|---|---|---|---|
| GO:0045121 membrane raft | IDA | 11877482 | ACCEPT | Two assay types + palmitoylation mutant + cholesterol control; exactly what the paper is about |
| GO:0046761 viral budding from plasma membrane | IDA | 11877482 | KEEP_AS_NON_CORE | Figs 5-6 support it; VP40 drives budding, GP contributes |
| GO:0044165 host cell ER | IMP | 21223600 | KEEP_AS_NON_CORE | Paper's own claim; overexpression caveat, no Golgi signal; code is really IDA (marker colocalisation) |
| GO:0030430 host cell cytoplasm | IDA | 20202662 | TOO_GENERAL | Paper has no GP-localisation assay (all imaging is of host clathrin/transferrin/Eps15); term is also entailed by the ER row |
| GO:0046718 symbiont entry into host cell | IMP | 20202662 | ACCEPT | Exactly the paper's result, and GP's core function |
New CACAO pattern worth adding to the taxonomy: mechanism paper read as a
localisation — an entry-pathway inhibitor study, whose only microscopy is of host
trafficking machinery, yielding an IDA cellular-component row on the viral protein.
It is the mirror image of "phenotype as process": here a process paper is converted
into a component annotation.
ChEBI:8984, sodium dodecylACCEPT 22, KEEP_AS_NON_CORE 4 (GO:0039587 tetherin suppression, GO:0042802 identical
protein binding, GO:0044165 host cell ER, GO:0046761 budding), TOO_GENERAL 5
(GO:0019062, GO:0030430, GO:0039663, GO:0052031, GO:0075509 — each a strict ancestor of
a term kept in this review), plus 2 NEW molecular functions: GO:0046789 host cell
surface receptor binding and GO:0035662 Toll-like receptor 4 binding. GOA gives GP no
molecular function at all apart from lipid binding and identical protein binding,
which is a real gap for the protein whose entire job is binding host receptors.
Three source defects are recorded: the ChEBI:8984 (SDS) WITH/FROM on the DisProt
lipid-binding IPI row; IMP where the assay is IDA on the CACAO host-cell-ER row; and
WRONG_REFERENCE (confidence CONFIRMED) on the CACAO host-cell-cytoplasm row, whose
cited paper contains no GP-localisation experiment.
Note for the schema: core_functions.locations cannot take GO:0055036 virion membrane
or GO:0019031 viral envelope, because GOCellularLocationEnum is reachable only from
GO:0110165 cellular anatomical structure and virion components sit outside it. For a
virion surface protein that is where the core activity happens, so the virion membrane is
stated in the core-function descriptions instead.