Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005787 signal peptidase complex	IBA GO_REF:0000033	ACCEPT	Summary: SPCS1 is a constitutive accessory subunit of the ER signal peptidase complex; phylogenetic assignment is correct and reflects the core identity of the protein. Reason: Core complex membership, strongly supported experimentally (cryo-EM, ComplexPortal) and by UniProt. Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt Component of the signal peptidase complex paralog A (SPC-A) composed of a catalytic subunit SEC11A and three accessory subunits SPCS1, SPCS2 and SPCS3
GO:0045047 protein targeting to ER	IBA GO_REF:0000033	MODIFY	Summary: SPCS1 does not target nascent proteins to the ER (that is the role of SRP and the Sec61 translocon); it acts after translocation as part of the signal peptidase complex that cleaves the signal peptide. The phylogenetic term is mis-specified; the accurate process is signal peptide processing. Reason: The SPC functions downstream of ER targeting, on already-translocating substrates, to cleave the signal peptide. UniProt/ComplexPortal annotate this activity as signal peptide processing (GO:0006465), not protein targeting to ER. Proposed replacements: signal peptide processing Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt catalyzes the cleavage of N-terminal signal sequences from nascent proteins as they are translocated into the lumen of the endoplasmic reticulum
GO:0005787 signal peptidase complex	IEA GO_REF:0000002	ACCEPT	Summary: InterPro-based electronic assignment to the signal peptidase complex, consistent with experimental evidence. Reason: Correct core complex membership; redundant with experimental IPI/IBA evidence. Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt Component of the signal peptidase complex paralog A (SPC-A) composed of a catalytic subunit SEC11A and three accessory subunits SPCS1, SPCS2 and SPCS3
GO:0005789 endoplasmic reticulum membrane	IEA GO_REF:0000044	ACCEPT	Summary: SPCS1 is a multi-pass ER membrane protein; the subcellular-location-based electronic annotation is correct and reflects the core localization. Reason: Core localization, supported by experimental topology (PMID:8632014) and structure (PMID:34388369). Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0016020 membrane	IEA GO_REF:0000002	KEEP AS NON CORE	Summary: Generic membrane localization, a parent of the more informative ER membrane term. Reason: Correct but uninformative; the specific GO:0005789 (ER membrane) better captures SPCS1 localization. Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt Multi-pass membrane protein
GO:0005515 protein binding	IPI PMID:24009510 Signal peptidase complex subunit 1 participates in the assem...	KEEP AS NON CORE	Summary: IntAct capture of SPCS1 interaction with hepatitis C virus NS2; a real host-pathogen interaction but the bare protein binding term is uninformative. Reason: Real experimental interaction (HCV NS2/E2) but bare protein binding is uninformative per curation guidelines and reflects a secondary viral role. Supporting Evidence: PMID:24009510 SPCS1 was found to interact with both NS2 and E2
GO:0005787 signal peptidase complex	IPI PMID:34388369 Structure of the human signal peptidase complex reveals the ...	ACCEPT	Summary: ComplexPortal annotation of SPCS1 as a component of the signal peptidase complex, based on the cryo-EM structure of the human SPC. Reason: Definitive experimental (structural) evidence for SPC membership; this is the core identity of SPCS1. Supporting Evidence: PMID:34388369 the human SPC exists in two functional paralogs with distinct proteolytic subunits
GO:0005789 endoplasmic reticulum membrane	IDA PMID:34388369 Structure of the human signal peptidase complex reveals the ...	ACCEPT	Summary: Direct (structural) evidence places SPCS1 in the ER membrane as part of the SPC; correct core localization. Reason: IDA-supported ER membrane localization consistent with the multi-pass topology and the membrane-embedded SPC structure. Supporting Evidence: PMID:34388369 a transmembrane window collectively formed by all subunits locally thins the bilayer
GO:0016485 protein processing	IDA PMID:34388369 Structure of the human signal peptidase complex reveals the ...	ACCEPT	Summary: SPCS1 participates in proteolytic processing of preproteins as part of the signal peptidase complex; the more precise term is signal peptide processing (GO:0006465). Reason: Correct involvement in the SPC's proteolytic processing of substrates; supported by the structural study and ComplexPortal curation. The core process is signal peptide processing. Supporting Evidence: PMID:34388369 the determinants for signal peptide cleavage
GO:0005789 endoplasmic reticulum membrane	ISS GO_REF:0000024	ACCEPT	Summary: Sequence-similarity transfer of ER membrane localization from an ortholog; consistent with stronger experimental evidence. Reason: Correct core localization, redundant with IDA/IEA evidence. Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0005515 protein binding	IPI PMID:34388369 Structure of the human signal peptidase complex reveals the ...	KEEP AS NON CORE	Summary: Interactions with the other SPC subunits (SEC11A/SEC11C, SPCS2, SPCS3) captured during the structural study; the bare protein binding term is uninformative although the underlying intra-complex interactions are genuine and functionally relevant. Reason: Real intra-complex interactions (SPCS2, SPCS3, SEC11A/C) but bare protein binding is uninformative; the SPC membership is already captured by GO:0005787. Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt Within the complex, interacts with SPCS2 and SPCS3
GO:0005515 protein binding	IPI PMID:29593046 Host Factor SPCS1 Regulates the Replication of Japanese Ence...	KEEP AS NON CORE	Summary: IntAct capture of SPCS1 interaction with flaviviral NS2B; a real host-pathogen interaction but the bare protein binding term is uninformative. Reason: Real experimental interaction (flavivirus NS2B) but bare protein binding is uninformative and reflects a secondary viral role. Supporting Evidence: PMID:29593046 SPCS1 was found to interact with nonstructural protein 2B (NS2B)
GO:0019068 virion assembly	IMP PMID:24009510 Signal peptidase complex subunit 1 participates in the assem...	KEEP AS NON CORE	Summary: SPCS1 knockdown markedly reduces production of infectious HCV by impairing formation of the membrane-associated NS2-E2 complex; a real experimental phenotype but a host-pathogen (secondary) role rather than SPCS1's core cellular function. Reason: Experimentally supported viral host-factor phenotype; not the core housekeeping function of SPCS1. Supporting Evidence: PMID:24009510 SPCS1 plays a key role in the formation of the membrane-associated NS2-E2 complex via its interaction with NS2 and E2 PMID:35130329
GO:0019068 virion assembly	IMP PMID:29593046 Host Factor SPCS1 Regulates the Replication of Japanese Ence...	KEEP AS NON CORE	Summary: SPCS1 loss reduces JEV virion assembly through interaction with NS2B; a real experimental viral phenotype but a secondary host-pathogen role. Reason: Experimentally supported viral host-factor phenotype; not the core cellular function. Supporting Evidence: PMID:29593046 The loss of SPCS1 function markedly reduced intracellular virion assembly and the production of infectious JEV particles
GO:0019082 viral protein processing	IMP PMID:27383988 A CRISPR screen defines a signal peptide processing pathway ...	KEEP AS NON CORE	Summary: A genome-wide CRISPR screen showed SPCS1 is required for proper cleavage of flavivirus structural proteins (prM and E); a real experimental phenotype but a secondary host-pathogen role. Reason: Experimentally supported viral host-factor role in processing flaviviral structural proteins; secondary to SPCS1's core function in cellular signal peptide processing. Supporting Evidence: PMID:27383988 a subset of endoplasmic reticulum-associated signal peptidase complex (SPCS) proteins was necessary for proper cleavage of the flavivirus structural proteins (prM and E) and secretion of viral particles
GO:0005789 endoplasmic reticulum membrane	TAS Reactome:R-HSA-422051	ACCEPT	Summary: Reactome curation of SPCS1 ER membrane localization (preproghrelin signal peptide cleavage context). Reason: Correct core localization; redundant with experimental evidence. Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0005789 endoplasmic reticulum membrane	TAS Reactome:R-HSA-9918795	ACCEPT	Summary: Reactome curation of SPCS1 ER membrane localization (flavivirus signalase cleavage context). Reason: Correct core localization; redundant with experimental evidence. Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0005789 endoplasmic reticulum membrane	TAS Reactome:R-HSA-9918871	ACCEPT	Summary: Reactome curation of SPCS1 ER membrane localization (signalase cleavage context). Reason: Correct core localization; redundant with experimental evidence. Supporting Evidence: file:human/SPCS1/SPCS1-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0005787 signal peptidase complex	TAS PMID:8632014 Membrane topology of the 12- and the 25-kDa subunits of the ...	ACCEPT	Summary: Early biochemical/topology study identifying SPC12 (SPCS1) as the 12-kDa subunit of the mammalian signal peptidase complex. Reason: Correct core complex membership; the historical reference that cloned and characterized SPC12 as an SPC subunit. Supporting Evidence: PMID:8632014 We have determined the cDNA sequence of the remaining 12-kDa subunit (SPC12)
GO:0005789 endoplasmic reticulum membrane	IDA PMID:8632014 Membrane topology of the 12- and the 25-kDa subunits of the ...	ACCEPT	Summary: Direct topology study placing SPC12 (SPCS1) in the ER (microsomal) membrane, spanning it twice with cytosol-facing termini. Reason: IDA-supported ER membrane localization with experimentally determined topology. Supporting Evidence: PMID:8632014 Both polypeptides span the membrane twice with their N and C termini facing the cytosol
GO:0006508 proteolysis	TAS PMID:8632014 Membrane topology of the 12- and the 25-kDa subunits of the ...	KEEP AS NON CORE	Summary: General proteolysis annotation derived from SPCS1 being a subunit of the signal peptidase complex. SPCS1 itself is non-catalytic, and the cytosol-facing topology argues it is not directly involved in the lumenal cleavage; the specific process is signal peptide processing. Reason: Generic parent term; SPCS1 is a non-catalytic accessory subunit and the cited paper explicitly concluded it is likely involved in processes other than enzymatic signal-sequence cleavage. The informative process term is GO:0006465 signal peptide processing. Supporting Evidence: PMID:8632014 SPC12 and SPC25 are likely to be involved in processes other than the enzymatic cleavage of the signal sequence

Core Functions

Non-catalytic accessory subunit of the ER signal peptidase complex, contributing to the architecture (membrane-thinning transmembrane window) and substrate selectivity of the complex that cleaves signal peptides from secretory and membrane preproteins.

Molecular Function:

structural molecule activity

Cellular Locations:

endoplasmic reticulum membrane

In Complex:

signal peptidase complex

Supporting Evidence:

file:human/SPCS1/SPCS1-uniprot.txt
Component of the signal peptidase complex paralog A (SPC-A) composed of a catalytic subunit SEC11A and three accessory subunits SPCS1, SPCS2 and SPCS3
PMID:34388369
a transmembrane window collectively formed by all subunits locally thins the bilayer

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000024

Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping

PMID:8632014

Membrane topology of the 12- and the 25-kDa subunits of the mammalian signal peptidase complex.

SPC12 (SPCS1) is the 12-kDa subunit of the mammalian SPC; it spans the membrane twice with N and C termini facing the cytosol and minimal lumenal domains, indicating a non-catalytic role.

PMID:24009510

Signal peptidase complex subunit 1 participates in the assembly of hepatitis C virus through an interaction with E2 and NS2.

SPCS1 interacts with HCV NS2 and E2 and is required for assembly of infectious HCV particles, without affecting structural-protein processing, host secretion, entry, RNA replication, or release.

PMID:27383988

A CRISPR screen defines a signal peptide processing pathway required by flaviviruses.

SPCS1 is required for proper cleavage of flavivirus structural proteins (prM, E) and secretion of viral particles; loss reduces yield of WNV, DENV, ZIKV, YFV, JEV, and HCV.

PMID:29593046

Host Factor SPCS1 Regulates the Replication of Japanese Encephalitis Virus through Interactions with Transmembrane Domains of NS2B.

SPCS1 interacts with the transmembrane domains of flaviviral NS2B and is required for post-translational processing of JEV proteins and virion assembly, but not entry, RNA replication, or translation.

PMID:34388369

Structure of the human signal peptidase complex reveals the determinants for signal peptide cleavage.

Cryo-EM structures of the two human SPC paralogs (SEC11A and SEC11C variants); the active site abuts the ER membrane where a transmembrane window collectively formed by all subunits locally thins the bilayer, generating specificity based on signal-peptide hydrophobic-segment length.

PMID:35130329

SPCS1-Dependent E2-p7 processing determines HCV Assembly efficiency.

Loss of SPCS1 specifically impairs SPC-mediated processing of the HCV E2-p7 junction (a suboptimal cleavage site); efficient separation of E2 and p7 renders SPCS1 dispensable for assembly, establishing that SPCS1 facilitates assembly by enhancing presentation of the suboptimal E2-p7 junction to the SPC active site, paralleling its role at the flaviviral C-prM junction.

PMID:33577859

Signal peptidase complex subunit 1 is an essential Zika virus host factor in placental trophoblasts.

A pooled CRISPR/Cas9 screen in placental trophoblasts identified ER membrane complex and signal peptide processing genes as Zika virus host factors, and validated SPCS1 as crucial for ZIKV replication in trophoblasts.

Reactome:R-HSA-422051

Cleavage of the signal peptide of Preproghrelin

Reactome:R-HSA-9918795

Signalase cleaves prM-E-NS1-NS2A

Reactome:R-HSA-9918871

Signalase cleaves prepro-NS4B

file:human/SPCS1/SPCS1-uniprot.txt

UniProt entry Q9Y6A9 (SPCS1_HUMAN), signal peptidase complex subunit 1

Non-catalytic accessory subunit of the ER signal peptidase complex (SPC-A with SEC11A and SPC-C with SEC11C, each also containing SPCS2 and SPCS3); multi-pass ER membrane protein; dispensable for SPC enzymatic activity; host factor for flavivirus/HCV structural-protein processing and assembly.

Suggested Experiments

Experiment: Reconstitute the SEC11A- and SEC11C-paralog signal peptidase complexes in vitro with and without SPCS1 and measure cleavage kinetics across a panel of substrates with varying signal-peptide h-region lengths to define SPCS1's contribution to activity and selectivity.

Experiment: Targeted SPCS1 degradation (e.g., degron) followed by quantitative N-terminomics to identify cellular preproteins whose signal-peptide cleavage depends on SPCS1.

Deep Research

Falcon

(SPCS1-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 34 citations 2 artifacts 2026-06-12T03:26:03.158529

Edison artifact artifact-00 (text/markdown)

## Context ID: pqac-00000025 The requested information can be found in the Graphical Abstract (page 1) and Figure 2 (page 4). The Graphical Abstract provides a (image/png)

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 SPCS1 (UniProt Q9Y6A9) Functional Annotation

Executive summary

Signal peptidase complex subunit 1 (SPCS1, also called SPC12) is a non-catalytic, ER-resident membrane subunit of the human signal peptidase complex (SPC) that contributes to SPC architecture and substrate selectivity for signal peptide cleavage. Structural work indicates SPCS1 participates in forming a “transmembrane window” that thins the ER membrane near the catalytic site to discriminate short signal peptides from longer transmembrane helices. Beyond canonical signal peptide removal, recent work supports a SPCS1-dependent quality-control role in which SPC performs noncanonical cleavage of misfolded/unassembled membrane proteins and couples this to ER-associated degradation (ERAD). In infection biology, multiple genetic screens and mechanistic studies show SPCS1 is a strong host dependency factor for Flaviviridae, acting mainly at post-replication stages by enabling specific, suboptimal SPC cleavage events required for virion assembly.

1) Target verification (identity, synonyms, organism)

The gene symbol SPCS1 in humans corresponds to the protein commonly referred to as SPC12 (microsomal signal peptidase 12 kDa subunit), an accessory subunit of the ER signal peptidase complex (SPC). Structural and mechanistic studies of the human SPC explicitly list SPC12/SPCS1 among the four subunits of each SPC paralog, consistent with the UniProt identity provided (Q9Y6A9). (liaci2021structureofthe pages 1-3)

2) Key concepts and definitions (current understanding)

2.1 Signal peptides and cleavage determinants

Signal peptides (SPs) classically comprise three regions: an N-terminal basic n-region, a hydrophobic h-region (often ~7–15 residues), and a more polar c-region (~3–7 residues) containing the cleavage site. Canonical cleavage typically prefers small, neutral residues at the −1 and −3 positions and disfavors proline near the cleavage site. (chung2024spc2modulatessubstrate pages 1-2, liaci2021structureofthe pages 1-3, liaci2021structureofthe pages 3-4)

2.2 The eukaryotic signal peptidase complex (SPC)

The ER-resident SPC is a membrane-embedded serine protease complex that removes signal peptides from nascent secretory and membrane proteins as they enter the ER. In humans, SPC exists as two functional paralogs that differ in the proteolytic subunit (SEC11A vs SEC11C) but share the same accessory subunits (SPCS1/SPC12, SPCS2/SPC25, SPCS3/SPC22/23). (liaci2021structureofthe pages 1-3, liaci2021structureofthe pages 3-4)

Catalysis resides in SEC11A/C, where a Ser–His–Asp catalytic triad forms the active site. SPCS1 is not the catalytic subunit; rather, it contributes to the membrane-embedded architecture that positions substrates and shapes specificity. (liaci2021structureofthe pages 1-3, chung2024spc2modulatessubstrate pages 1-2)

3) Molecular function and mechanism of SPCS1

3.1 Complex membership and ER localization

SPCS1 is an ER-resident membrane subunit of the human SPC and is present in both SPC paralogs: SPC-A (SEC11A-containing) and SPC-C (SEC11C-containing). (liaci2021structureofthe pages 1-3, liaci2021structureofthe media 82841cab)

A key structural depiction of SPC subunit organization (including SPC12/SPCS1) is shown in Liaci et al. (Graphical Abstract and Figure 2). (liaci2021structureofthe media 82841cab, liaci2021structureofthe media ab792889)

3.2 Structural role in the “transmembrane window” and membrane thinning

Cryo-EM and supporting simulations indicate that all SPC subunits collectively form a transmembrane window that locally thins the ER membrane adjacent to the luminal active site. This provides a physical mechanism to preferentially accommodate short SP h-regions while excluding longer transmembrane helices, thereby enforcing selectivity in signal peptide cleavage. SPCS1 contributes transmembrane elements to this architecture, supporting specificity without providing catalytic residues. (liaci2021structureofthe pages 1-3, liaci2021structureofthe media 82841cab)

3.3 Accessory-subunit control of substrate selection and quality control (recent emphasis)

Recent mechanistic synthesis suggests that accessory subunits (including SPCS1) help ensure accurate substrate discrimination and cleavage site selection, rather than catalysis itself. In yeast genetics, accessory subunit perturbations compromise substrate discrimination and can increase incorrect transmembrane cleavage, supporting the general concept that SPCS1-like subunits contribute to quality control/fidelity. (chung2024spc2modulatessubstrate pages 1-2)

A major recent development is the proposal that the human SPC is not only a signal-peptide peptidase but also a quality-control enzyme for membrane proteins, with SPCS1 acting as a recruitment factor/exosite for “noncanonical” substrates. Specifically, proteome-scale analysis identified ~1500 membrane proteins with putative cryptic SPC cleavage sites (reported as ~18% of the human membrane proteome; with ~80% of predicted sites after internal TMDs). Several substrates were experimentally validated (e.g., Cx32/Cx26/Cx30.3, PMP22, iRhom2, Hrd1). (zanotti2023characterisationofthe pages 49-53, zanotti2023characterisationofthe pages 1-8, zanotti2023characterisationofthe pages 34-38)

Functionally, SPCS1 knockout does not necessarily disrupt canonical signal sequence cleavage for tested substrates, but strongly reduces noncanonical cleavage of multiple membrane proteins; in one assay, prolactin secretion increased ~4-fold upon SPCS1 loss/depletion, consistent with SPCS1 acting as a specificity/selection factor rather than being required for general SPC catalysis. (zanotti2023characterisationofthe pages 34-38, zanotti2023characterisationofthe pages 53-57)

3.4 Coupling to ERAD via Hrd1 (mechanistic linkage)

Evidence supports direct physical and functional coupling between SPC/SPCS1-mediated noncanonical cleavage and ER-associated degradation (ERAD). Hrd1 (ERAD E3 ligase) binds SPC subunits (including SPCS1 and SEC11A) in co-immunoprecipitation experiments, and endogenous SPCS1 co-precipitates Hrd1. Functional turnover assays show that an SPC-derived fragment from a mutant membrane substrate decreases ~50% over 4 hours in wild-type cells but is completely stable in Hrd1 knockout cells, and inhibition of p97/VCP causes fragment accumulation—supporting a model in which SPC cleavage precedes Hrd1- and p97-dependent dislocation and degradation. (zanotti2023characterisationofthe pages 43-49)

4) Recent developments and latest research (prioritizing 2023–2024)

4.1 2024: Accessory subunits and fidelity in SPC substrate selection

A 2024 Journal of Cell Biology study (in yeast, with direct reference to human cryo-EM) emphasizes that while Sec11 is catalytic, accessory subunits (Spc1/SPCS1, Spc2/SPCS2) contribute transmembrane helices and influence substrate selection and cleavage site identification, consistent with a conserved accessory-subunit contribution to fidelity rather than catalysis. (chung2024spc2modulatessubstrate pages 1-2)

4.2 2023: SPC/SPCS1 as a membrane-protein quality-control enzyme

A 2023 body of work summarized in Zanotti’s thesis highlights a broadened functional role for SPC: SPCS1-dependent noncanonical cleavage of misfolded/unassembled membrane proteins, with proteome-scale estimates of candidate substrates and mechanistic coupling to ERAD/Hrd1. This “SPC-as-QC” framing is a major conceptual advance beyond the classic view of SPC as solely a cotranslational signal peptide remover. (zanotti2023characterisationofthe pages 49-53, zanotti2023characterisationofthe pages 43-49, zanotti2023characterisationofthe pages 34-38)

4.3 2024: ER-centric host-directed antiviral strategies (contextualizing SPCS1/SPC)

A 2024 review in npj Viruses frames the ER as a central hub in flavivirus protein translocation and processing, and highlights host-directed intervention opportunities, including inhibitors of signal peptidase cleavage (e.g., cavinafungin) and ER translocation inhibitors (cotransins, apratoxins). While this review does not focus on SPCS1 specifically in the excerpted pages, it supports the importance of ER processing machinery targeted by viruses and as druggable biology. (verhaegen2024theendoplasmicreticulum pages 6-7, verhaegen2024theendoplasmicreticulum pages 13-14)

5) Current applications and real-world implementations

5.1 Host-directed antiviral research targeting ER processing

Flaviviridae dependence on SPCS1 is supported by genome-wide CRISPR screening and validation showing that SPCS1 loss results in markedly reduced yield for multiple flaviviruses (e.g., WNV, DENV, ZIKV, YFV, JEV) and HCV, with viral translation/replication often relatively preserved—consistent with a post-replication role (protein processing/assembly). (zhang2016acrisprscreen pages 1-2)

Quantitative example (HCV): In HCV systems, SPCS1 loss impaired E2–p7 processing and caused major assembly/titer defects, including reported up to ~3-log reductions in extracellular titers in one experimental system and abrogation/minimization of defects when E2 and p7 were separated by an EMCV IRES (bypassing the SPC junction processing constraint). (alzahrani2022spcs1dependente2p7processing pages 5-7)

Mechanistic example (JEV): SPCS1 regulates JEV propagation primarily at posttranslational processing/assembly and interacts with NS2B transmembrane domains; mutations in NS2B transmembrane regions weaken NS2B–SPCS1 interaction, supporting a direct virus–host interface. (ma2018hostfactorspcs1 pages 1-2, ma2018hostfactorspcs1 pages 2-5)

These findings position SPCS1/SPC biology as a foundation for host-directed antiviral strategies, although translation to clinic remains limited and safety constraints are expected because SPC is central to secretory pathway function. (zhang2016acrisprscreen pages 1-2, alzahrani2022spcs1dependente2p7processing pages 2-3)

A 2024 review cites cavinafungin as a natural product that selectively interferes with Zika and dengue replication by inhibiting host signal peptidase activity, illustrating practical use of SPC pathway inhibition as an antiviral approach. (verhaegen2024theendoplasmicreticulum pages 13-14)

6) Expert opinions and authoritative synthesis

Across structural biology, cell biology, and virology, a convergent interpretation is that SPCS1 does not catalyze peptide bond cleavage but contributes to (i) SPC architecture that couples the catalytic site to the membrane interface and (ii) substrate discrimination, including specialized handling of “difficult” or suboptimal cleavage sites. Structural work frames specificity partly as a physical property of membrane thinning and transmembrane architecture, while more recent cell biology emphasizes an exosite-like recruitment role for noncanonical substrates in membrane-protein proteostasis. (liaci2021structureofthe pages 1-3, zanotti2023characterisationofthe pages 53-57, zanotti2023characterisationofthe pages 49-53)

In virology, multiple reviews of CRISPR screens highlight SPCS1 as an ER-localized dependency factor repeatedly rediscovered as essential for flavivirus replication/assembly and note that pharmacological modulation of ER translocation/processing machinery can inhibit DENV and ZIKV replication, supporting host-directed strategy rationale. (kanojia2022flavivirus–hostinteractionlandscape pages 7-9)

7) Relevant statistics and data highlights

Proteome-scale QC substrate prevalence: ~1500 membrane proteins with predicted cryptic SPC cleavage sites; ~18% of the human membrane proteome; ~80% of predicted sites after internal TMDs. (zanotti2023characterisationofthe pages 49-53)
ERAD coupling kinetics: An SPC-derived fragment from a mutant membrane substrate decreases ~50% over 4 hours in wild-type cells but is stable in Hrd1 knockout cells (fragment turnover depends on Hrd1); p97/VCP inhibition increases fragment accumulation. (zanotti2023characterisationofthe pages 43-49)
HCV assembly effect sizes: SPCS1 loss can produce up to ~3-log reductions in extracellular infectious titers in one HCV system, consistent with a strong post-replication assembly/processing phenotype linked to E2–p7 processing. (alzahrani2022spcs1dependente2p7processing pages 5-7)

8) Disease/phenotype associations (cautious interpretation)

OpenTargets aggregates association evidence linking SPCS1 to dengue disease (highest among returned examples), and lower-scoring associations to osteoarthritis, cataract, and bipolar disorder. These are association-level signals and do not by themselves establish causal mechanisms; the dengue link is biologically plausible given strong experimental evidence for SPCS1 as a flavivirus host factor. (OpenTargets Search: -SPCS1)

9) Visual evidence supporting SPC/SPCS1 structure

Liaci et al. provide a graphical abstract and a figure illustrating the architecture of human SPC paralogs, labeling SPC12/SPCS1 and showing the clamp-like arrangement and membrane thinning/transmembrane window concept. (liaci2021structureofthe media 82841cab, liaci2021structureofthe media ab792889)

10) Practical functional-annotation conclusion

Primary function: SPCS1 is a non-catalytic SPC subunit that enables accurate and selective ER signal peptide cleavage by shaping SPC membrane architecture and substrate discrimination, and it extends SPC function into membrane-protein quality control by promoting noncanonical cleavage of exposed transmembrane segments of misfolded/unassembled proteins and coupling this to ERAD. (liaci2021structureofthe pages 1-3, zanotti2023characterisationofthe pages 49-53, zanotti2023characterisationofthe pages 43-49)

Localization: ER membrane, within the SPC complex at the lumenal membrane interface. (liaci2021structureofthe pages 1-3, liaci2021structureofthe media 82841cab)

Pathways: Secretory pathway protein biogenesis (Sec61 translocation → SPC cleavage), proteostasis/ER stress response and ERAD coupling (Hrd1/p97). (chung2024spc2modulatessubstrate pages 1-2, zanotti2023characterisationofthe pages 43-49)

High-impact application area: Host-directed antiviral research for Flaviviridae, where SPCS1 controls processing/assembly steps dependent on suboptimal cleavage sites. (zhang2016acrisprscreen pages 1-2, alzahrani2022spcs1dependente2p7processing pages 5-7)

Summary table

Aspect	Key points	Evidence type	Representative sources (year and URL)
Identity / aliases	SPCS1 is the human gene matching UniProt Q9Y6A9; protein name signal peptidase complex subunit 1, also called SPC12 / microsomal signal peptidase 12 kDa subunit. It belongs to the SPCS1 family and is a non-catalytic accessory subunit of the ER signal peptidase complex, not the peptidase active site itself. (liaci2021structureofthe pages 1-3)	Database-supported identity; structural/biochemical complex assignment	Liaci et al., 2021, https://doi.org/10.2139/ssrn.3778304; OpenTargets SPCS1 target entry/context, accessed via tool output (OpenTargets Search: -SPCS1)
Complex membership (SPC-A / SPC-C)	Human SPC exists as two paralogs: SPC-A = SPCS1 + SPCS2 + SPCS3 + SEC11A and SPC-C = SPCS1 + SPCS2 + SPCS3 + SEC11C. SPCS1 is therefore shared between both paralogs. Cryo-EM figures show SPC12/SPCS1 as one of the membrane subunits contributing to the clamp-like architecture around the catalytic core. (liaci2021structureofthe pages 1-3, liaci2021structureofthe pages 3-4, liaci2021structureofthe media 82841cab)	Cryo-EM structure; native complex proteomics	Liaci et al., 2021, https://doi.org/10.2139/ssrn.3778304
Subcellular localization / topology	SPCS1 is ER-resident and membrane-embedded within the endoplasmic reticulum signal peptidase complex at the ER membrane/lumenal interface. It contributes transmembrane helices to the membrane-embedded body of SPC and helps shape the transmembrane window adjacent to the lumenal active site. (liaci2021structureofthe pages 1-3, chung2024spc2modulatessubstrate pages 1-2)	Structural biology; membrane topology inference	Liaci et al., 2021, https://doi.org/10.2139/ssrn.3778304; Gemmer & Förster, 2020, https://doi.org/10.1242/jcs.231340
Molecular function	SPCS1 functions as an accessory, non-proteolytic SPC subunit. The catalytic Ser-His-Asp triad resides in SEC11A/SEC11C, whereas SPCS1 supports proper complex architecture, activity tuning, and substrate handling rather than catalysis. (liaci2021structureofthe pages 1-3, chung2024spc2modulatessubstrate pages 1-2)	Structure-function analysis; comparative genetics	Liaci et al., 2021, https://doi.org/10.2139/ssrn.3778304; Chung et al., 2024, https://doi.org/10.1083/jcb.202211035
Mechanistic role: membrane thinning window	The SPC forms a transmembrane window that locally thins the ER membrane; all subunits, including SPCS1, contribute to this architecture. This membrane deformation helps the complex distinguish short signal-peptide h-regions from longer transmembrane helices, a major determinant of cleavage specificity. (liaci2021structureofthe pages 1-3, liaci2021structureofthe media 82841cab)	Cryo-EM; molecular dynamics; mechanistic modeling	Liaci et al., 2021, https://doi.org/10.2139/ssrn.3778304
Mechanistic role: substrate selection / cleavage determinants	Canonical substrates have signal peptides with n-, h-, and c-regions; the c-region usually contains small neutral residues at -1 and -3 and disfavors proline at +1. Accessory subunits including SPCS1 help enforce correct substrate and cleavage-site selection rather than direct catalysis. (chung2024spc2modulatessubstrate pages 1-2, liaci2021structureofthe pages 1-3, liaci2021structureofthe pages 3-4)	Structural comparison; biochemical rules; genetics	Chung et al., 2024, https://doi.org/10.1083/jcb.202211035; Liaci et al., 2021, https://doi.org/10.2139/ssrn.3778304
Mechanistic role: noncanonical QC cleavage / exosite model	Beyond canonical signal peptide removal, SPCS1 is implicated in SPC-dependent quality control of membrane proteins. Work summarized in 2023 indicates SPCS1 may provide an exosite/recruitment function for noncanonical substrates with cryptic cleavage sites adjacent to type II-oriented TMDs; this enables cleavage of misfolded/unassembled membrane proteins and promotes their disposal. (zanotti2023characterisationofthe pages 57-60, zanotti2023characterisationofthe pages 53-57, zanotti2023characterisationofthe pages 1-8)	Cell biology; knockout phenotyping; proteomics; mechanistic inference	Zanotti, 2023, https://doi.org/10.11588/heidok.00033417
Key pathways / partners	SPCS1 acts within the secretory protein biogenesis pathway downstream of ER targeting/translocation. SPC accessory subunits make transient/functional links with the Sec61 translocon, and SPCS1-dependent noncanonical cleavage is coupled to ER-associated degradation (ERAD), particularly involving Hrd1. (chung2024spc2modulatessubstrate pages 1-2, zanotti2023characterisationofthe pages 53-57, zanotti2023characterisationofthe pages 57-60)	Structural cell biology; interaction/functional studies	Gemmer & Förster, 2020, https://doi.org/10.1242/jcs.231340; Chung et al., 2024, https://doi.org/10.1083/jcb.202211035; Zanotti, 2023, https://doi.org/10.11588/heidok.00033417
Viral relevance	SPCS1 is a validated host dependency factor for Flaviviridae, with strong evidence from CRISPR/KO studies showing major defects in production of WNV, DENV, ZIKV, YFV, JEV, and HCV when SPCS1 is lost; viral translation/replication is often relatively preserved, indicating a post-replication protein-processing/assembly role. (zhang2016acrisprscreen pages 2-3, zhang2016acrisprscreen pages 1-2, rother2021signalpeptidasecomplex pages 1-2)	Genome-wide CRISPR; knockout/complementation; virology	Zhang et al., 2016, https://doi.org/10.1038/nature18625; Rother & Naumann, 2021, https://doi.org/10.1016/j.virusres.2021.198338; Verhaegen & Vermeire, 2024, https://doi.org/10.1038/s44298-024-00031-7
Viral mechanism details	In JEV, SPCS1 interacts with NS2B transmembrane domains and supports posttranslational processing/virion assembly rather than entry or early RNA replication. In HCV, SPCS1 facilitates E2-p7 processing; SPCS1 loss caused near 1-log lower intracellular RNA at late times and up to ~3-log lower extracellular titers for one HCV system, while an engineered E2-EMCV-p7 construct bypassed much of the defect. (alzahrani2022spcs1dependente2p7processing pages 5-7, ma2018hostfactorspcs1 pages 2-5, ma2018hostfactorspcs1 pages 1-2)	BiFC/interactome; knockout; rescue; immunoblot; infectivity assays	Ma et al., 2018, https://doi.org/10.1128/jvi.00197-18; Alzahrani et al., 2022, https://doi.org/10.1371/journal.ppat.1010310
Disease / trait associations (OpenTargets)	OpenTargets reports disease/trait associations for dengue disease (strongest among returned examples in this query output), and lower-scoring associations with osteoarthritis, hip osteoarthritis, cataract, and bipolar disorder. These should be interpreted cautiously as association-level evidence, not necessarily direct mechanism. (OpenTargets Search: -SPCS1)	Target-disease association aggregation	OpenTargets platform result for SPCS1 via tool context (no single paper URL provided in tool output); association evidence includes literature mapped in OpenTargets context (OpenTargets Search: -SPCS1)

Table: This table summarizes the verified identity, ER signal peptidase complex role, mechanisms, pathway context, and virology relevance of human SPCS1 (UniProt Q9Y6A9). It is designed as a compact reference for functional annotation with context-linked citations.

References

(liaci2021structureofthe pages 1-3): A. Manuel Liaci, Barbara Steigenberger, Sem Tamara, Paulo Cesar Telles de Souza, Mariska Gröllers-Mulderij, Patrick Ogrissek, Siewert Jan Marrink, Richard Scheltema, and Friedrich Förster. Structure of the human signal peptidase complex reveals the determinants for signal peptide cleavage. Jan 2021. URL: https://doi.org/10.2139/ssrn.3778304, doi:10.2139/ssrn.3778304. This article has 148 citations.
(chung2024spc2modulatessubstrate pages 1-2): Yeonji Chung, Chewon Yim, Gilberto P. Pereira, Sungjoon Son, Lisbeth R. Kjølbye, Lauren E. Mazurkiewicz, Amy M. Weeks, Friedrich Förster, Gunnar von Heijne, Paulo C.T. Souza, and Hyun Kim. Spc2 modulates substrate- and cleavage site-selection in the yeast signal peptidase complex. Journal of Cell Biology, Nov 2024. URL: https://doi.org/10.1083/jcb.202211035, doi:10.1083/jcb.202211035. This article has 4 citations and is from a highest quality peer-reviewed journal.
(liaci2021structureofthe pages 3-4): A. Manuel Liaci, Barbara Steigenberger, Sem Tamara, Paulo Cesar Telles de Souza, Mariska Gröllers-Mulderij, Patrick Ogrissek, Siewert Jan Marrink, Richard Scheltema, and Friedrich Förster. Structure of the human signal peptidase complex reveals the determinants for signal peptide cleavage. Jan 2021. URL: https://doi.org/10.2139/ssrn.3778304, doi:10.2139/ssrn.3778304. This article has 148 citations.
(liaci2021structureofthe media 82841cab): A. Manuel Liaci, Barbara Steigenberger, Sem Tamara, Paulo Cesar Telles de Souza, Mariska Gröllers-Mulderij, Patrick Ogrissek, Siewert Jan Marrink, Richard Scheltema, and Friedrich Förster. Structure of the human signal peptidase complex reveals the determinants for signal peptide cleavage. Jan 2021. URL: https://doi.org/10.2139/ssrn.3778304, doi:10.2139/ssrn.3778304. This article has 148 citations.
(liaci2021structureofthe media ab792889): A. Manuel Liaci, Barbara Steigenberger, Sem Tamara, Paulo Cesar Telles de Souza, Mariska Gröllers-Mulderij, Patrick Ogrissek, Siewert Jan Marrink, Richard Scheltema, and Friedrich Förster. Structure of the human signal peptidase complex reveals the determinants for signal peptide cleavage. Jan 2021. URL: https://doi.org/10.2139/ssrn.3778304, doi:10.2139/ssrn.3778304. This article has 148 citations.
(zanotti2023characterisationofthe pages 49-53): Andrea Zanotti. Characterisation of the human signal peptidase complex as a quality control enzyme for membrane proteins. Text, Jan 2023. URL: https://doi.org/10.11588/heidok.00033417, doi:10.11588/heidok.00033417. This article has 0 citations and is from a peer-reviewed journal.
(zanotti2023characterisationofthe pages 1-8): Andrea Zanotti. Characterisation of the human signal peptidase complex as a quality control enzyme for membrane proteins. Text, Jan 2023. URL: https://doi.org/10.11588/heidok.00033417, doi:10.11588/heidok.00033417. This article has 0 citations and is from a peer-reviewed journal.
(zanotti2023characterisationofthe pages 34-38): Andrea Zanotti. Characterisation of the human signal peptidase complex as a quality control enzyme for membrane proteins. Text, Jan 2023. URL: https://doi.org/10.11588/heidok.00033417, doi:10.11588/heidok.00033417. This article has 0 citations and is from a peer-reviewed journal.
(zanotti2023characterisationofthe pages 53-57): Andrea Zanotti. Characterisation of the human signal peptidase complex as a quality control enzyme for membrane proteins. Text, Jan 2023. URL: https://doi.org/10.11588/heidok.00033417, doi:10.11588/heidok.00033417. This article has 0 citations and is from a peer-reviewed journal.
(zanotti2023characterisationofthe pages 43-49): Andrea Zanotti. Characterisation of the human signal peptidase complex as a quality control enzyme for membrane proteins. Text, Jan 2023. URL: https://doi.org/10.11588/heidok.00033417, doi:10.11588/heidok.00033417. This article has 0 citations and is from a peer-reviewed journal.
(verhaegen2024theendoplasmicreticulum pages 6-7): Marijke Verhaegen and Kurt Vermeire. The endoplasmic reticulum (er): a crucial cellular hub in flavivirus infection and potential target site for antiviral interventions. npj Viruses, Jun 2024. URL: https://doi.org/10.1038/s44298-024-00031-7, doi:10.1038/s44298-024-00031-7. This article has 37 citations.
(verhaegen2024theendoplasmicreticulum pages 13-14): Marijke Verhaegen and Kurt Vermeire. The endoplasmic reticulum (er): a crucial cellular hub in flavivirus infection and potential target site for antiviral interventions. npj Viruses, Jun 2024. URL: https://doi.org/10.1038/s44298-024-00031-7, doi:10.1038/s44298-024-00031-7. This article has 37 citations.
(zhang2016acrisprscreen pages 1-2): Rong Zhang, Jonathan J. Miner, Matthew J. Gorman, Keiko Rausch, Holly Ramage, James P. White, Adam Zuiani, Ping Zhang, Estefania Fernandez, Qiang Zhang, Kimberly A. Dowd, Theodore C. Pierson, Sara Cherry, and Michael S. Diamond. A crispr screen defines a signal peptide processing pathway required by flaviviruses. Nature, 535:164-168, Jun 2016. URL: https://doi.org/10.1038/nature18625, doi:10.1038/nature18625. This article has 453 citations and is from a highest quality peer-reviewed journal.
(alzahrani2022spcs1dependente2p7processing pages 5-7): Nabeel Alzahrani, Ming-Jhan Wu, Carla F. Sousa, Olga V. Kalinina, Christoph Welsch, and MinKyung Yi. Spcs1-dependent e2-p7 processing determines hcv assembly efficiency. PLOS Pathogens, 18:e1010310, Feb 2022. URL: https://doi.org/10.1371/journal.ppat.1010310, doi:10.1371/journal.ppat.1010310. This article has 8 citations and is from a highest quality peer-reviewed journal.
(ma2018hostfactorspcs1 pages 1-2): Le Ma, Fang Li, Jing-Wei Zhang, Wei Li, Dong-Ming Zhao, Han Wang, Rong-Hong Hua, and Zhi-Gao Bu. Host factor spcs1 regulates the replication of japanese encephalitis virus through interactions with transmembrane domains of ns2b. Journal of Virology, Jun 2018. URL: https://doi.org/10.1128/jvi.00197-18, doi:10.1128/jvi.00197-18. This article has 35 citations and is from a domain leading peer-reviewed journal.
(ma2018hostfactorspcs1 pages 2-5): Le Ma, Fang Li, Jing-Wei Zhang, Wei Li, Dong-Ming Zhao, Han Wang, Rong-Hong Hua, and Zhi-Gao Bu. Host factor spcs1 regulates the replication of japanese encephalitis virus through interactions with transmembrane domains of ns2b. Journal of Virology, Jun 2018. URL: https://doi.org/10.1128/jvi.00197-18, doi:10.1128/jvi.00197-18. This article has 35 citations and is from a domain leading peer-reviewed journal.
(alzahrani2022spcs1dependente2p7processing pages 2-3): Nabeel Alzahrani, Ming-Jhan Wu, Carla F. Sousa, Olga V. Kalinina, Christoph Welsch, and MinKyung Yi. Spcs1-dependent e2-p7 processing determines hcv assembly efficiency. PLOS Pathogens, 18:e1010310, Feb 2022. URL: https://doi.org/10.1371/journal.ppat.1010310, doi:10.1371/journal.ppat.1010310. This article has 8 citations and is from a highest quality peer-reviewed journal.
(kanojia2022flavivirus–hostinteractionlandscape pages 7-9): Aditi Kanojia, Mansi Sharma, Rishad Shiraz, and Shashank Tripathi. Flavivirus–host interaction landscape visualized through genome-wide crispr screens. Viruses, 14:2164, Sep 2022. URL: https://doi.org/10.3390/v14102164, doi:10.3390/v14102164. This article has 12 citations.
(OpenTargets Search: -SPCS1): Open Targets Query (-SPCS1, 5 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(zanotti2023characterisationofthe pages 57-60): Andrea Zanotti. Characterisation of the human signal peptidase complex as a quality control enzyme for membrane proteins. Text, Jan 2023. URL: https://doi.org/10.11588/heidok.00033417, doi:10.11588/heidok.00033417. This article has 0 citations and is from a peer-reviewed journal.
(zhang2016acrisprscreen pages 2-3): Rong Zhang, Jonathan J. Miner, Matthew J. Gorman, Keiko Rausch, Holly Ramage, James P. White, Adam Zuiani, Ping Zhang, Estefania Fernandez, Qiang Zhang, Kimberly A. Dowd, Theodore C. Pierson, Sara Cherry, and Michael S. Diamond. A crispr screen defines a signal peptide processing pathway required by flaviviruses. Nature, 535:164-168, Jun 2016. URL: https://doi.org/10.1038/nature18625, doi:10.1038/nature18625. This article has 453 citations and is from a highest quality peer-reviewed journal.
(rother2021signalpeptidasecomplex pages 1-2): Marion Rother and Michael Naumann. Signal peptidase complex subunit 1 is an essential zika virus host factor in placental trophoblasts. Apr 2021. URL: https://doi.org/10.1016/j.virusres.2021.198338, doi:10.1016/j.virusres.2021.198338. This article has 4 citations and is from a peer-reviewed journal.

Artifacts

Edison artifact artifact-00

Citations

liaci2021structureofthe pages 1-3
zanotti2023characterisationofthe pages 43-49
zhang2016acrisprscreen pages 1-2
verhaegen2024theendoplasmicreticulum pages 13-14
zanotti2023characterisationofthe pages 49-53
liaci2021structureofthe pages 3-4
zanotti2023characterisationofthe pages 1-8
zanotti2023characterisationofthe pages 34-38
zanotti2023characterisationofthe pages 53-57
verhaegen2024theendoplasmicreticulum pages 6-7
zanotti2023characterisationofthe pages 57-60
zhang2016acrisprscreen pages 2-3
rother2021signalpeptidasecomplex pages 1-2
https://doi.org/10.2139/ssrn.3778304;
https://doi.org/10.2139/ssrn.3778304
https://doi.org/10.1242/jcs.231340
https://doi.org/10.1083/jcb.202211035
https://doi.org/10.1083/jcb.202211035;
https://doi.org/10.11588/heidok.00033417
https://doi.org/10.1242/jcs.231340;
https://doi.org/10.1038/nature18625;
https://doi.org/10.1016/j.virusres.2021.198338;
https://doi.org/10.1038/s44298-024-00031-7
https://doi.org/10.1128/jvi.00197-18;
https://doi.org/10.1371/journal.ppat.1010310
https://doi.org/10.2139/ssrn.3778304,
https://doi.org/10.1083/jcb.202211035,
https://doi.org/10.11588/heidok.00033417,
https://doi.org/10.1038/s44298-024-00031-7,
https://doi.org/10.1038/nature18625,
https://doi.org/10.1371/journal.ppat.1010310,
https://doi.org/10.1128/jvi.00197-18,
https://doi.org/10.3390/v14102164,
https://doi.org/10.1016/j.virusres.2021.198338,

📚 Additional Documentation

Notes

(SPCS1-notes.md)

SPCS1 (Signal peptidase complex subunit 1) — review notes

UniProt: Q9Y6A9 (SPCS1_HUMAN); aka SPC12, "Microsomal signal peptidase 12 kDa subunit". 169 aa, multi-pass ER membrane protein (two TM helices, residues 94-114 and 116-136). HGNC:23401, gene on chr 3.

Core identity and function

SPCS1 is one of the three non-catalytic accessory subunits (SPCS1, SPCS2, SPCS3) of the eukaryotic ER signal peptidase complex (SPC). The catalytic subunits are SEC11A (SPC-A) or SEC11C (SPC-C). SPCS1 is dispensable for SPC enzymatic (peptidase) activity.

UniProt FUNCTION: "Component of the signal peptidase complex (SPC) which catalyzes the cleavage of N-terminal signal sequences from nascent proteins as they are translocated into the lumen of the endoplasmic reticulum (PubMed:34388369). Dispensable for SPC enzymatic activity (By similarity)." [UniProt Q9Y6A9]
UniProt SUBUNIT: "Component of the signal peptidase complex paralog A (SPC-A) composed of a catalytic subunit SEC11A and three accessory subunits SPCS1, SPCS2 and SPCS3 ... Within the complex, interacts with SPCS2 and SPCS3 (PubMed:34388369). The complex induces a local thinning of the ER membrane which is used to measure the length of the signal peptide (SP) h-region of protein substrates."
Cryo-EM structure of human SPC: PMID:34388369 establishes SPCS1 as a structural component of the complex and reports phosphorylation.
Membrane topology established in PMID:8632014.

So core function = SPC complex membership (GO:0005787), signal peptide processing / protein processing involvement (GO:0006465 / GO:0016485), ER membrane localization (GO:0005789). NOT a catalytic MF.

Secondary / non-core: viral (flavivirus + HCV) processing

SPCS1 was identified in CRISPR/host-factor screens as required for flavivirus and HCV propagation. This is a host-factor role hijacked by viruses; secondary, not the core cellular function.

HCV: PMID:24009510 "identified signal peptidase complex subunit 1 (SPCS1) ... Silencing of endogenous SPCS1 resulted in markedly reduced production of infectious HCV ... SPCS1 was found to interact with both NS2 and E2 ... SPCS1 plays a key role in the formation of the membrane-associated NS2-E2 complex." Note: in this paper, "Propagation of Japanese encephalitis virus was not affected by knockdown of SPCS1" — i.e. virion-assembly role here is HCV-specific via NS2/E2 interaction.
Flaviviruses (CRISPR screen): PMID:27383988 — SPCS1 required; "Plays a key role in the post-translational processing of flaviviral structural proteins prM, E, and NS1" (UniProt).
JEV: PMID:29593046 "The loss of SPCS1 function markedly reduced intracellular virion assembly and the production of infectious JEV particles but did not affect cell entry, RNA replication, or translation ... SPCS1 was found to interact with nonstructural protein 2B (NS2B) ... thereby influencing the posttranslational processing of JEV proteins and the assembly of virions." (Note: contradicts the HCV paper's statement that JEV is unaffected; later work supports a JEV role.)

Annotation assessment summary

GO:0005787 signal peptidase complex (IBA, IEA, IPI, TAS) — CORE, ACCEPT. Multiple lines.
GO:0005789 ER membrane (IDA, IEA, ISS, TAS) — CORE localization, ACCEPT.
GO:0016020 membrane (IEA, InterPro) — generic parent of ER membrane; KEEP_AS_NON_CORE (less informative).
GO:0045047 protein targeting to ER (IBA) — SPC acts at the ER on translocated substrates; the IBA term is somewhat broad but defensible as involvement; KEEP_AS_NON_CORE (more accurate process is signal peptide processing).
GO:0016485 protein processing (IDA, ComplexPortal) — ACCEPT; reflects SP cleavage. (GO:0006465 signal peptide processing is the more specific term; ComplexPortal also annotates GO:0006465 per UniProt DR line.)
GO:0006508 proteolysis (TAS) — generic; the complex is a peptidase but SPCS1 itself is non-catalytic. KEEP_AS_NON_CORE / MARK_AS_OVER_ANNOTATED — it's a parent of signal peptide processing and SPCS1 is not catalytic. Keep as non-core.
GO:0005515 protein binding (IPI x several) — KEEP_AS_NON_CORE (bare protein binding, uninformative). Interactions with SPCS2/SPCS3 (intra-complex) and with viral proteins.
GO:0019068 virion assembly (IMP, PMID:24009510 HCV; PMID:29593046 JEV) — viral host-factor; KEEP_AS_NON_CORE.
GO:0019082 viral protein processing (IMP, PMID:27383988) — viral host-factor; KEEP_AS_NON_CORE.

Falcon deep-research findings (incorporated 2026-06)

SPCS1 facilitates HCV assembly specifically by enhancing SPC-mediated processing of the suboptimal E2-p7 junction; loss of SPCS1 impairs E2-p7 separation, and engineering efficient E2/p7 separation makes SPCS1 dispensable for assembly PMID:35130329. This establishes a common mechanism with flavivirus C-prM processing: SPCS1 exquisitely regulates SPC cleavage at specific, suboptimal target sites PMID:35130329. (Verified PubMed; not cached.)
Independent CRISPR screen in placental trophoblasts validated SPCS1 as essential for Zika virus replication, with host factors enriched in the ER membrane complex and signal peptide processing pathway PMID:33577859. Adds a trophoblast/placental disease context (microcephaly, vertical transmission) to the flavivirus host-factor role. (Verified PubMed; not cached.)
Falcon emphasizes a structural model (Liaci et al. 2021 = PMID:34388369, already cited as the cryo-EM paper) in which all subunits including SPCS1 contribute to a transmembrane "window" that locally thins the ER bilayer (~26% thinning in simulations) — a molecular ruler discriminating short signal-peptide h-regions (mean ~11 aa) from longer TM helices (>18-20 aa excluded). Consistent with existing review; no new reference needed.
Falcon cites a 2024 yeast study (Chung et al. = PMID:39565596) showing the accessory subunit Spc2/SPCS2 modulates substrate and cleavage-site selection via membrane thinning — relevant to the general accessory-subunit fidelity concept but specific to SPCS2, not SPCS1; logged in the SPCS2 review instead.
Falcon's "SPC-as-quality-control-enzyme" framing (SPCS1 as a recruitment/exosite factor for noncanonical membrane-protein cleavage, ~1500 cryptic-site substrates, ERAD/Hrd1 coupling) derives from Zanotti 2023, a Heidelberg PhD thesis (doi:10.11588/heidok.00033417) with no PMID and not peer-reviewed primary literature. Interesting hypothesis but NOT added as a reference (unverifiable as a PMID; thesis-level evidence). Noted here only.
Review-level/background sources (Verhaegen & Vermeire 2024 npj Viruses ER/flavivirus review; Kanojia 2022 flavivirus CRISPR review) reinforce SPC/SPCS1 as a druggable host-directed antiviral target (e.g. cavinafungin inhibits signal peptidase), but are background reviews not adding gene-specific SPCS1 findings beyond what is already captured; not added.

Pn Notes

(SPCS1-pn-notes.md)

SPCS1 PN Consistency Notes

Generated: 2026-06-18
Project: PROTEOSTASIS
Scope: PN consistency rereview against local AIGR review and available deep-research artifacts
UniProt: Q9Y6A9
AIGR review status: COMPLETE
Review batch: proteostasis-batch-2026-06-11
Batch change status: added

Source Files Checked

AIGR review YAML: present - genes/human/SPCS1/SPCS1-ai-review.yaml
AIGR review HTML: missing - genes/human/SPCS1/SPCS1-ai-review.html
Gene notes: present - genes/human/SPCS1/SPCS1-notes.md
GOA TSV: present - genes/human/SPCS1/SPCS1-goa.tsv
UniProt record: present - genes/human/SPCS1/SPCS1-uniprot.txt
PN dossier: projects/PROTEOSTASIS/reports/phase1_dossiers/SPCS1.md
PN consistency section: projects/PROTEOSTASIS/reports/phase1_dossiers/_sections/SPCS1.md
PN projection report: projects/PROTEOSTASIS/reports/pn_projection/pn_projected_gene_go_summary.tsv
PN mapping audit: projects/PROTEOSTASIS/reports/pn_mapping_audit/current_mapping_scrutiny.tsv

Deep Research Files

genes/human/SPCS1/SPCS1-deep-research-falcon.md

AIGR Review Snapshot

Description: SPCS1 (signal peptidase complex subunit 1, also SPC12, the microsomal signal peptidase 12 kDa subunit) is a small (169 aa) multi-pass endoplasmic reticulum membrane protein that is one of the three non-catalytic accessory subunits (with SPCS2 and SPCS3) of the eukaryotic ER signal peptidase complex (SPC). The SPC removes N-terminal signal sequences from secretory and membrane preproteins as they are translocated into the ER lumen; its catalytic activity resides in the SEC11A or SEC11C subunits, and SPCS1 is dispensable for enzymatic cleavage. SPCS1 spans the ER membrane twice with both termini facing the cytosol and only minimal lumenal exposure, and together with the other subunits it shapes a transmembrane "window" that locally thins the lipid bilayer, contributing to substrate selectivity for signal-peptide hydrophobic regions shorter than about 18-20 residues. Beyond its housekeeping role in signal peptide processing, SPCS1 acts as a host factor exploited by flaviviruses (West Nile, Dengue, Zika, yellow fever, Japanese encephalitis viruses) and hepatitis C virus, where it promotes post-translational processing of viral structural proteins and assembly of infectious virions through interactions with viral membrane proteins such as HCV NS2/E2 and flaviviral NS2B.
Existing/core annotation action counts: ACCEPT: 12; KEEP_AS_NON_CORE: 8; MODIFY: 1

PN Consistency Summary

Consistency: Strong agreement. Deep research, review YAML, and PN all describe SPCS1 as a non-catalytic accessory SPC subunit (multi-pass, cytosol-facing termini, dispensable for catalysis; contributes to membrane-thinning window/selectivity) plus a flavivirus/HCV host factor. PN node correctly captures complex membership without ascribing catalysis. No contradictions.
PN story / NEW pressure: PN asserts only CC membership (GO:0005787) and broad transport (GO:0015031). GO:0005787 already in review (IBA/IEA/IPI/TAS). The transport class GO:0015031 is broader than the review, which deliberately MODIFIES the IBA GO:0045047 (protein targeting to ER) to GO:0006465 signal peptide processing — i.e. the review argues SPCS1 acts downstream of targeting, not in transport. So PN's GO:0015031 (protein transport) projection slightly over-reaches for an accessory peptidase subunit. The accurate process is GO:0006465. No new MF justified (non-catalytic). Conclude: membership already captured; PN transport-class projection over-reaches vs review's signal-peptide-processing framing.
Evidence alignment: PN row carries no titles; review's accessory/topology evidence (PMID:8632014, PMID:34388369) and viral host-factor evidence (PMID:24009510, 27383988, 29593046, 35130329, 33577859) plus falcon deep research (liaci2021, chung2024) all converge. Congruent.
Verdict: CONSISTENT on membership; PN's protein-transport class projection over-reaches (review's GO:0006465 signal peptide processing is more accurate). No gene-YAML edit needed.

Full Consistency Review

UniProt: Q9Y6A9 (SPC12) · batch: proteostasis-batch-2026-06-11 · review status: COMPLETE
PN placement: ER proteostasis|Protein transport|ER signal peptidase; PN-node mapping: group mapped, ok_for_propagation_to_go, GO:0005787 (signal peptidase complex); class GO:0015031 (protein transport).
Consistency: Strong agreement. Deep research, review YAML, and PN all describe SPCS1 as a non-catalytic accessory SPC subunit (multi-pass, cytosol-facing termini, dispensable for catalysis; contributes to membrane-thinning window/selectivity) plus a flavivirus/HCV host factor. PN node correctly captures complex membership without ascribing catalysis. No contradictions.
PN story / NEW pressure: PN asserts only CC membership (GO:0005787) and broad transport (GO:0015031). GO:0005787 already in review (IBA/IEA/IPI/TAS). The transport class GO:0015031 is broader than the review, which deliberately MODIFIES the IBA GO:0045047 (protein targeting to ER) to GO:0006465 signal peptide processing — i.e. the review argues SPCS1 acts downstream of targeting, not in transport. So PN's GO:0015031 (protein transport) projection slightly over-reaches for an accessory peptidase subunit. The accurate process is GO:0006465. No new MF justified (non-catalytic). Conclude: membership already captured; PN transport-class projection over-reaches vs review's signal-peptide-processing framing.
Mapping strategy: GO:0005787 CC mapping is correct. The class-level GO:0015031 protein transport is the questionable projection: for accessory SPC subunits the review's signal peptide processing (GO:0006465) is the defensible BP, and protein transport over-states an upstream-transport role SPCS1 does not have (parallels the broader-than-warranted precedent). Suggest the node distinguish accessory (membership/selectivity, GO:0006465) from catalytic members.
Evidence alignment: PN row carries no titles; review's accessory/topology evidence (PMID:8632014, PMID:34388369) and viral host-factor evidence (PMID:24009510, 27383988, 29593046, 35130329, 33577859) plus falcon deep research (liaci2021, chung2024) all converge. Congruent.
Verdict: CONSISTENT on membership; PN's protein-transport class projection over-reaches (review's GO:0006465 signal peptide processing is more accurate). No gene-YAML edit needed.
Recommended edits: [MAP] At the "ER signal peptidase" class, prefer GO:0006465 signal peptide processing over GO:0015031 protein transport as the BP projection for accessory subunits (SPCS1/2), reflecting that SPCS1 acts downstream of ER targeting (matches review MODIFY of GO:0045047→GO:0006465).

PN Dossier Context

review_batch: proteostasis-batch-2026-06-11
review_yaml: genes/human/SPCS1/SPCS1-ai-review.yaml
PN workbook rows: 1

PN row 1: ER proteostasis | Protein transport | ER signal peptidase

UniProt: Q9Y6A9
In branches: ER
PN-node mapping records (path + ancestors):
- [group] ER proteostasis|Protein transport|ER signal peptidase
  status=mapped scope=ok_for_propagation_to_go GO=[GO:0005787 signal peptidase complex]
  rationale: This PN group denotes ER signal peptidase complex components. The matching GO cellular-component term is the direct 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 (2)

GO:0015031 protein transport | scope=ok_for_propagation_to_go | goa_status=new_to_goa | from=ER proteostasis|Protein transport
GO:0005787 signal peptidase complex | scope=ok_for_propagation_to_go | goa_status=already_in_goa_exact | from=ER proteostasis|Protein transport|ER signal peptidase

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.

📄 View Raw YAML

id: Q9Y6A9
gene_symbol: SPCS1
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: SPCS1 (signal peptidase complex subunit 1, also SPC12, the microsomal signal peptidase 12 kDa subunit) is a small (169 aa) multi-pass endoplasmic reticulum membrane protein that is one of the three non-catalytic accessory subunits (with SPCS2 and SPCS3) of the eukaryotic ER signal peptidase complex (SPC). The SPC removes N-terminal signal sequences from secretory and membrane preproteins as they are translocated into the ER lumen; its catalytic activity resides in the SEC11A or SEC11C subunits, and SPCS1 is dispensable for enzymatic cleavage. SPCS1 spans the ER membrane twice with both termini facing the cytosol and only minimal lumenal exposure, and together with the other subunits it shapes a transmembrane "window" that locally thins the lipid bilayer, contributing to substrate selectivity for signal-peptide hydrophobic regions shorter than about 18-20 residues. Beyond its housekeeping role in signal peptide processing, SPCS1 acts as a host factor exploited by flaviviruses (West Nile, Dengue, Zika, yellow fever, Japanese encephalitis viruses) and hepatitis C virus, where it promotes post-translational processing of viral structural proteins and assembly of infectious virions through interactions with viral membrane proteins such as HCV NS2/E2 and flaviviral NS2B.
existing_annotations:
- term:
    id: GO:0005787
    label: signal peptidase complex
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: part_of
  review:
    summary: SPCS1 is a constitutive accessory subunit of the ER signal peptidase complex; phylogenetic assignment is correct and reflects the core identity of the protein.
    action: ACCEPT
    reason: Core complex membership, strongly supported experimentally (cryo-EM, ComplexPortal) and by UniProt.
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: 'Component of the signal peptidase complex paralog A (SPC-A) composed of a catalytic subunit SEC11A and three accessory subunits SPCS1, SPCS2 and SPCS3'
- term:
    id: GO:0045047
    label: protein targeting to ER
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: SPCS1 does not target nascent proteins to the ER (that is the role of SRP and the Sec61 translocon); it acts after translocation as part of the signal peptidase complex that cleaves the signal peptide. The phylogenetic term is mis-specified; the accurate process is signal peptide processing.
    action: MODIFY
    reason: The SPC functions downstream of ER targeting, on already-translocating substrates, to cleave the signal peptide. UniProt/ComplexPortal annotate this activity as signal peptide processing (GO:0006465), not protein targeting to ER.
    proposed_replacement_terms:
    - id: GO:0006465
      label: signal peptide processing
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: catalyzes the cleavage of N-terminal signal sequences from nascent proteins as they are translocated into the lumen of the endoplasmic reticulum
- term:
    id: GO:0005787
    label: signal peptidase complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: part_of
  review:
    summary: InterPro-based electronic assignment to the signal peptidase complex, consistent with experimental evidence.
    action: ACCEPT
    reason: Correct core complex membership; redundant with experimental IPI/IBA evidence.
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: 'Component of the signal peptidase complex paralog A (SPC-A) composed of a catalytic subunit SEC11A and three accessory subunits SPCS1, SPCS2 and SPCS3'
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: SPCS1 is a multi-pass ER membrane protein; the subcellular-location-based electronic annotation is correct and reflects the core localization.
    action: ACCEPT
    reason: Core localization, supported by experimental topology (PMID:8632014) and structure (PMID:34388369).
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: located_in
  review:
    summary: Generic membrane localization, a parent of the more informative ER membrane term.
    action: KEEP_AS_NON_CORE
    reason: Correct but uninformative; the specific GO:0005789 (ER membrane) better captures SPCS1 localization.
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: Multi-pass membrane protein
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:24009510
  qualifier: enables
  review:
    summary: IntAct capture of SPCS1 interaction with hepatitis C virus NS2; a real host-pathogen interaction but the bare protein binding term is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Real experimental interaction (HCV NS2/E2) but bare protein binding is uninformative per curation guidelines and reflects a secondary viral role.
    supported_by:
    - reference_id: PMID:24009510
      supporting_text: SPCS1 was found to interact with both NS2 and E2
- term:
    id: GO:0005787
    label: signal peptidase complex
  evidence_type: IPI
  original_reference_id: PMID:34388369
  qualifier: part_of
  review:
    summary: ComplexPortal annotation of SPCS1 as a component of the signal peptidase complex, based on the cryo-EM structure of the human SPC.
    action: ACCEPT
    reason: Definitive experimental (structural) evidence for SPC membership; this is the core identity of SPCS1.
    supported_by:
    - reference_id: PMID:34388369
      supporting_text: the human SPC exists in two functional paralogs with distinct proteolytic subunits
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IDA
  original_reference_id: PMID:34388369
  qualifier: located_in
  review:
    summary: Direct (structural) evidence places SPCS1 in the ER membrane as part of the SPC; correct core localization.
    action: ACCEPT
    reason: IDA-supported ER membrane localization consistent with the multi-pass topology and the membrane-embedded SPC structure.
    supported_by:
    - reference_id: PMID:34388369
      supporting_text: a transmembrane window collectively formed by all subunits locally thins the bilayer
- term:
    id: GO:0016485
    label: protein processing
  evidence_type: IDA
  original_reference_id: PMID:34388369
  qualifier: involved_in
  review:
    summary: SPCS1 participates in proteolytic processing of preproteins as part of the signal peptidase complex; the more precise term is signal peptide processing (GO:0006465).
    action: ACCEPT
    reason: Correct involvement in the SPC's proteolytic processing of substrates; supported by the structural study and ComplexPortal curation. The core process is signal peptide processing.
    supported_by:
    - reference_id: PMID:34388369
      supporting_text: the determinants for signal peptide cleavage
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: located_in
  review:
    summary: Sequence-similarity transfer of ER membrane localization from an ortholog; consistent with stronger experimental evidence.
    action: ACCEPT
    reason: Correct core localization, redundant with IDA/IEA evidence.
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:34388369
  qualifier: enables
  review:
    summary: Interactions with the other SPC subunits (SEC11A/SEC11C, SPCS2, SPCS3) captured during the structural study; the bare protein binding term is uninformative although the underlying intra-complex interactions are genuine and functionally relevant.
    action: KEEP_AS_NON_CORE
    reason: Real intra-complex interactions (SPCS2, SPCS3, SEC11A/C) but bare protein binding is uninformative; the SPC membership is already captured by GO:0005787.
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: Within the complex, interacts with SPCS2 and SPCS3
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:29593046
  qualifier: enables
  review:
    summary: IntAct capture of SPCS1 interaction with flaviviral NS2B; a real host-pathogen interaction but the bare protein binding term is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Real experimental interaction (flavivirus NS2B) but bare protein binding is uninformative and reflects a secondary viral role.
    supported_by:
    - reference_id: PMID:29593046
      supporting_text: SPCS1 was found to interact with nonstructural protein 2B (NS2B)
- term:
    id: GO:0019068
    label: virion assembly
  evidence_type: IMP
  original_reference_id: PMID:24009510
  qualifier: involved_in
  review:
    summary: SPCS1 knockdown markedly reduces production of infectious HCV by impairing formation of the membrane-associated NS2-E2 complex; a real experimental phenotype but a host-pathogen (secondary) role rather than SPCS1's core cellular function.
    action: KEEP_AS_NON_CORE
    reason: Experimentally supported viral host-factor phenotype; not the core housekeeping function of SPCS1.
    supported_by:
    - reference_id: PMID:24009510
      supporting_text: SPCS1 plays a key role in the formation of the membrane-associated NS2-E2 complex via its interaction with NS2 and E2
    - reference_id: PMID:35130329
- term:
    id: GO:0019068
    label: virion assembly
  evidence_type: IMP
  original_reference_id: PMID:29593046
  qualifier: involved_in
  review:
    summary: SPCS1 loss reduces JEV virion assembly through interaction with NS2B; a real experimental viral phenotype but a secondary host-pathogen role.
    action: KEEP_AS_NON_CORE
    reason: Experimentally supported viral host-factor phenotype; not the core cellular function.
    supported_by:
    - reference_id: PMID:29593046
      supporting_text: The loss of SPCS1 function markedly reduced intracellular virion assembly and the production of infectious JEV particles
- term:
    id: GO:0019082
    label: viral protein processing
  evidence_type: IMP
  original_reference_id: PMID:27383988
  qualifier: involved_in
  review:
    summary: A genome-wide CRISPR screen showed SPCS1 is required for proper cleavage of flavivirus structural proteins (prM and E); a real experimental phenotype but a secondary host-pathogen role.
    action: KEEP_AS_NON_CORE
    reason: Experimentally supported viral host-factor role in processing flaviviral structural proteins; secondary to SPCS1's core function in cellular signal peptide processing.
    supported_by:
    - reference_id: PMID:27383988
      supporting_text: a subset of endoplasmic reticulum-associated signal peptidase complex (SPCS) proteins was necessary for proper cleavage of the flavivirus structural proteins (prM and E) and secretion of viral particles
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-422051
  qualifier: located_in
  review:
    summary: Reactome curation of SPCS1 ER membrane localization (preproghrelin signal peptide cleavage context).
    action: ACCEPT
    reason: Correct core localization; redundant with experimental evidence.
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9918795
  qualifier: located_in
  review:
    summary: Reactome curation of SPCS1 ER membrane localization (flavivirus signalase cleavage context).
    action: ACCEPT
    reason: Correct core localization; redundant with experimental evidence.
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9918871
  qualifier: located_in
  review:
    summary: Reactome curation of SPCS1 ER membrane localization (signalase cleavage context).
    action: ACCEPT
    reason: Correct core localization; redundant with experimental evidence.
    supported_by:
    - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0005787
    label: signal peptidase complex
  evidence_type: TAS
  original_reference_id: PMID:8632014
  qualifier: part_of
  review:
    summary: Early biochemical/topology study identifying SPC12 (SPCS1) as the 12-kDa subunit of the mammalian signal peptidase complex.
    action: ACCEPT
    reason: Correct core complex membership; the historical reference that cloned and characterized SPC12 as an SPC subunit.
    supported_by:
    - reference_id: PMID:8632014
      supporting_text: We have determined the cDNA sequence of the remaining 12-kDa subunit (SPC12)
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IDA
  original_reference_id: PMID:8632014
  qualifier: located_in
  review:
    summary: Direct topology study placing SPC12 (SPCS1) in the ER (microsomal) membrane, spanning it twice with cytosol-facing termini.
    action: ACCEPT
    reason: IDA-supported ER membrane localization with experimentally determined topology.
    supported_by:
    - reference_id: PMID:8632014
      supporting_text: Both polypeptides span the membrane twice with their N and C termini facing the cytosol
- term:
    id: GO:0006508
    label: proteolysis
  evidence_type: TAS
  original_reference_id: PMID:8632014
  qualifier: involved_in
  review:
    summary: General proteolysis annotation derived from SPCS1 being a subunit of the signal peptidase complex. SPCS1 itself is non-catalytic, and the cytosol-facing topology argues it is not directly involved in the lumenal cleavage; the specific process is signal peptide processing.
    action: KEEP_AS_NON_CORE
    reason: Generic parent term; SPCS1 is a non-catalytic accessory subunit and the cited paper explicitly concluded it is likely involved in processes other than enzymatic signal-sequence cleavage. The informative process term is GO:0006465 signal peptide processing.
    supported_by:
    - reference_id: PMID:8632014
      supporting_text: SPC12 and SPC25 are likely to be involved in processes other than the enzymatic cleavage of the signal sequence
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity
  findings: []
- 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
  findings: []
- id: PMID:8632014
  title: Membrane topology of the 12- and the 25-kDa subunits of the mammalian signal peptidase complex.
  findings:
  - statement: SPC12 (SPCS1) is the 12-kDa subunit of the mammalian SPC; it spans the membrane twice with N and C termini facing the cytosol and minimal lumenal domains, indicating a non-catalytic role.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Establishes SPCS1 (SPC12) topology and SPC membership and the inference that it is not the catalytic subunit.
- id: PMID:24009510
  title: Signal peptidase complex subunit 1 participates in the assembly of hepatitis C virus through an interaction with E2 and NS2.
  findings:
  - statement: SPCS1 interacts with HCV NS2 and E2 and is required for assembly of infectious HCV particles, without affecting structural-protein processing, host secretion, entry, RNA replication, or release.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Source of the HCV NS2/E2 interaction and virion-assembly host-factor role; secondary to SPCS1's core SPC function.
- id: PMID:27383988
  title: A CRISPR screen defines a signal peptide processing pathway required by flaviviruses.
  findings:
  - statement: SPCS1 is required for proper cleavage of flavivirus structural proteins (prM, E) and secretion of viral particles; loss reduces yield of WNV, DENV, ZIKV, YFV, JEV, and HCV.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Genome-wide CRISPR screen establishing the flavivirus host-factor role; secondary to the core cellular function.
- id: PMID:29593046
  title: Host Factor SPCS1 Regulates the Replication of Japanese Encephalitis Virus through Interactions with Transmembrane Domains of NS2B.
  findings:
  - statement: SPCS1 interacts with the transmembrane domains of flaviviral NS2B and is required for post-translational processing of JEV proteins and virion assembly, but not entry, RNA replication, or translation.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Mechanistic study of the flavivirus host-factor role via NS2B interaction; reaffirms SPCS1 is non-catalytic.
- id: PMID:34388369
  title: Structure of the human signal peptidase complex reveals the determinants for signal peptide cleavage.
  findings:
  - statement: Cryo-EM structures of the two human SPC paralogs (SEC11A and SEC11C variants); the active site abuts the ER membrane where a transmembrane window collectively formed by all subunits locally thins the bilayer, generating specificity based on signal-peptide hydrophobic-segment length.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Definitive structural study establishing SPCS1 as an accessory SPC subunit and the membrane-thinning architecture; basis for ComplexPortal annotations.
- id: PMID:35130329
  title: SPCS1-Dependent E2-p7 processing determines HCV Assembly efficiency.
  findings:
  - statement: Loss of SPCS1 specifically impairs SPC-mediated processing of the HCV E2-p7 junction (a suboptimal cleavage site); efficient separation of E2 and p7 renders SPCS1 dispensable for assembly, establishing that SPCS1 facilitates assembly by enhancing presentation of the suboptimal E2-p7 junction to the SPC active site, paralleling its role at the flaviviral C-prM junction.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (PMID:35130329, doi:10.1371/journal.ppat.1010310). Mechanistic study of the SPCS1 HCV host-factor role; supports the existing virion-assembly annotation. Secondary to the core SPC function. Not in publications cache, so no verbatim supporting_text added.
- id: PMID:33577859
  title: Signal peptidase complex subunit 1 is an essential Zika virus host factor in placental trophoblasts.
  findings:
  - statement: A pooled CRISPR/Cas9 screen in placental trophoblasts identified ER membrane complex and signal peptide processing genes as Zika virus host factors, and validated SPCS1 as crucial for ZIKV replication in trophoblasts.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (PMID:33577859, doi:10.1016/j.virusres.2021.198338). Corroborates the flavivirus host-factor role of SPCS1 in a placental-trophoblast context; secondary to the core SPC function. Not in publications cache, so no verbatim supporting_text added.
- id: Reactome:R-HSA-422051
  title: Cleavage of the signal peptide of Preproghrelin
  findings: []
- id: Reactome:R-HSA-9918795
  title: Signalase cleaves prM-E-NS1-NS2A
  findings: []
- id: Reactome:R-HSA-9918871
  title: Signalase cleaves prepro-NS4B
  findings: []
- id: file:human/SPCS1/SPCS1-uniprot.txt
  title: UniProt entry Q9Y6A9 (SPCS1_HUMAN), signal peptidase complex subunit 1
  findings:
  - statement: Non-catalytic accessory subunit of the ER signal peptidase complex (SPC-A with SEC11A and SPC-C with SEC11C, each also containing SPCS2 and SPCS3); multi-pass ER membrane protein; dispensable for SPC enzymatic activity; host factor for flavivirus/HCV structural-protein processing and assembly.
    reference_section_type: OTHER
core_functions:
- description: Non-catalytic accessory subunit of the ER signal peptidase complex, contributing to the architecture (membrane-thinning transmembrane window) and substrate selectivity of the complex that cleaves signal peptides from secretory and membrane preproteins.
  supported_by:
  - reference_id: file:human/SPCS1/SPCS1-uniprot.txt
    supporting_text: 'Component of the signal peptidase complex paralog A (SPC-A) composed of a catalytic subunit SEC11A and three accessory subunits SPCS1, SPCS2 and SPCS3'
  - reference_id: PMID:34388369
    supporting_text: a transmembrane window collectively formed by all subunits locally thins the bilayer
  molecular_function:
    id: GO:0005198
    label: structural molecule activity
  contributes_to_molecular_function:
    id: GO:0009003
    label: signal peptidase activity
  in_complex:
    id: GO:0005787
    label: signal peptidase complex
  locations:
  - id: GO:0005789
    label: endoplasmic reticulum membrane
proposed_new_terms: []
suggested_questions:
- question: Does SPCS1 modulate the substrate range or efficiency of the signal peptidase complex (e.g., selectivity for particular signal-peptide hydrophobic-region lengths), or is it purely structural?
- question: Is the flavivirus/HCV dependence on SPCS1 a direct consequence of its signal-peptidase accessory role, or a separable function mediated by direct binding to viral transmembrane proteins (NS2B, NS2/E2)?
suggested_experiments:
- description: Reconstitute the SEC11A- and SEC11C-paralog signal peptidase complexes in vitro with and without SPCS1 and measure cleavage kinetics across a panel of substrates with varying signal-peptide h-region lengths to define SPCS1's contribution to activity and selectivity.
- description: Targeted SPCS1 degradation (e.g., degron) followed by quantitative N-terminomics to identify cellular preproteins whose signal-peptide cleavage depends on SPCS1.

SPCS1

Gene Description

Existing Annotations Review

Core Functions

Non-catalytic accessory subunit of the ER signal peptidase complex, contributing to the architecture (membrane-thinning transmembrane window) and substrate selectivity of the complex that cleaves signal peptides from secretory and membrane preproteins.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Research Report: Human SPCS1 (UniProt Q9Y6A9) Functional Annotation

Executive summary

1) Target verification (identity, synonyms, organism)

2) Key concepts and definitions (current understanding)

2.1 Signal peptides and cleavage determinants

2.2 The eukaryotic signal peptidase complex (SPC)

3) Molecular function and mechanism of SPCS1

3.1 Complex membership and ER localization

3.2 Structural role in the “transmembrane window” and membrane thinning

3.3 Accessory-subunit control of substrate selection and quality control (recent emphasis)

3.4 Coupling to ERAD via Hrd1 (mechanistic linkage)

4) Recent developments and latest research (prioritizing 2023–2024)

4.1 2024: Accessory subunits and fidelity in SPC substrate selection

4.2 2023: SPC/SPCS1 as a membrane-protein quality-control enzyme

4.3 2024: ER-centric host-directed antiviral strategies (contextualizing SPCS1/SPC)

5) Current applications and real-world implementations

5.1 Host-directed antiviral research targeting ER processing

5.2 Proof-of-concept chemical modulation: cavinafungin and related ER-targeting agents

6) Expert opinions and authoritative synthesis

7) Relevant statistics and data highlights

8) Disease/phenotype associations (cautious interpretation)

9) Visual evidence supporting SPC/SPCS1 structure

10) Practical functional-annotation conclusion

Summary table

Artifacts

Citations

📚 Additional Documentation

Notes

SPCS1 (Signal peptidase complex subunit 1) — review notes

Core identity and function

Secondary / non-core: viral (flavivirus + HCV) processing

Annotation assessment summary

Falcon deep-research findings (incorporated 2026-06)

Pn Notes

SPCS1 PN Consistency Notes

Source Files Checked

Deep Research Files

AIGR Review Snapshot

PN Consistency Summary

Full Consistency Review

PN Dossier Context

PN row 1: ER proteostasis | Protein transport | ER signal peptidase

Projected GO annotations (2)

Note

📄 View Raw YAML