| Topic | Key claim | Evidence type | Specific quantitative/statistical detail if available | Source with year and URL/DOI |
|---|---|---|---|---|
| Identity / complex membership | Human SPCS2 (UniProt Q15005) is the signal peptidase complex subunit 2, a conserved non-catalytic/accessory subunit of the ER signal peptidase complex (SPC), which in higher eukaryotes contains SPCS1, SPCS2, SPCS3, and either SEC11A or SEC11C. Structural/functional work places SPCS2 outside the SEC11A/C+SPCS3 catalytic core. (pqac-00000006, pqac-00000007, pqac-00000008) | Structure; comparative cell biology; complex biochemistry | No direct human stoichiometric value reported in the cited excerpts; two SPC paralogs distinguished by SEC11A vs SEC11C. (pqac-00000006, pqac-00000008) | Chung et al., 2024, https://doi.org/10.1083/jcb.202211035; Zanotti, 2023, https://doi.org/10.11588/heidok.00033417 |
| Localization / topology | SPCS2 is an ER membrane component of SPC. Conserved structural analysis indicates Spc2/SPCS2 contributes much of the cytosolic face of the complex and includes additional transmembrane helices; SPC catalysis occurs at the ER lumenal side near the membrane. (pqac-00000006, pqac-00000008, pqac-00000010) | Structure; topology inference; comparative modeling | In yeast-based comparative analysis, human SPCS2 was noted to be structurally conserved with yeast Spc2 and to constitute most of the cytosolic part of SPC. (pqac-00000010) | Chung et al., 2024, https://doi.org/10.1083/jcb.202211035; Zanotti, 2023, https://doi.org/10.11588/heidok.00033417 |
| Mechanistic role | SPCS2/Spc2 helps determine substrate discrimination and cleavage-site selection by SPC, likely by promoting local membrane thinning and by presenting features of signal peptides/signal anchors to the complex. In mammals and yeast, Spc2/SPCS2 is also reported to mediate transient interaction with the Sec61 translocon via Sec61β. (pqac-00000006, pqac-00000007, pqac-00000009, pqac-00000010) | Genetics/mutagenesis; computational/MD; structure | Yeast functional data: Spc2 promotes cleavage of signal sequences with short n-regions and reduces cleavage of long n-region substrates; N# >16 substrates were more efficiently cleaved when Spc2 was absent or C-terminally truncated; at least n=3 independent replicates/data point in cited figure context; ~10% reduction in Sec11 and Spc3 abundance in spc2Δ cells in one quantitative analysis. (pqac-00000002, pqac-00000009, pqac-00000010) | Chung et al., 2024, https://doi.org/10.1083/jcb.202211035; Zanotti, 2023, https://doi.org/10.11588/heidok.00033417 |
| Noncanonical substrates / quality control | Beyond canonical signal peptide removal, human SPC participates in ER quality control by cleaving cryptic/noncanonical sites in membrane proteins; SPCS2 affects this process to varying extents, although SPCS1 appears more central as a recruitment/exosite factor. Validated or discussed substrates include Cx32, Cx26, Cx30.3, iRhom2, Hrd1, and Jaw1/IRAG2. (pqac-00000003, pqac-00000004, pqac-00000005, pqac-00000016, pqac-00000017, pqac-00000019) | Biochemistry; knockdown/KO; pulse-chase; inhibitor studies | Computational screening identified 262 membrane proteins with putative N-terminal cryptic SPC sites in one filtered set and ~1300 candidate proteins in a broader screen; iRhom2 cleavage quantification was reported with n=3–6 and significance markers *P<0.05, ***P<0.001; Cx32C201R cleavage quantification n=3 with *P<0.05, **P<0.01; post-translational Cx32C201R processing initiated ~30 min after synthesis. (pqac-00000001, pqac-00000005, pqac-00000019) | Zanotti, 2023, https://doi.org/10.11588/heidok.00033417; Kozono et al., 2023, https://doi.org/10.1242/jcs.260439 |
| Catalytic paralog specificity | Some noncanonical substrates show catalytic paralog selectivity: Jaw1/IRAG2 is cleaved by the SEC11A-containing SPC, not SEC11C. For Cx32, SEC11A knockdown did not block cleavage, consistent with possible compensation by SEC11C; cavinafungin blocked cleavage, indicating catalytic SPC dependence. SPCS2 is listed as an accessory component in these pathways. (pqac-00000017, pqac-00000018) | Biochemistry; knockdown; pharmacology | SEC11A depletion alone did not impair Cx32 cleavage in cited experiments; cavinafungin caused a complete block of noncanonical cleavage. (pqac-00000018) | Kozono et al., 2023, https://doi.org/10.1242/jcs.260439; Zanotti, 2023, https://doi.org/10.11588/heidok.00033417 |
| Viral interactions | SPCS2 is repeatedly identified as a host factor/interactor for viral proteins processed or assembled at the ER. In SARS-CoV-2 host–virus interactome studies, spike protein significantly bound the signal peptidase complex including SPCS2. In HCV AP-MS studies, SPCS2 interacted with both p7 and E2. (pqac-00000011, pqac-00000012, pqac-00000013, pqac-00000014, pqac-00000015) | AP-MS interactome; proximity labeling / affinity purification | HCV study scale: 12 p7 binders, 7 primary E2 interactors, and 24 NS4B interactors were detected; SPCS2 was among the host proteins interacting with both p7 and E2. SARS-CoV-2 interactome used SFB-TAP and BioID2 mapping approaches. (pqac-00000011, pqac-00000013) | Chen et al., 2021, https://doi.org/10.1101/2020.12.31.424961 and https://doi.org/10.15252/embj.2021107776; Matthaei et al., 2024, https://doi.org/10.1128/spectrum.02562-22 |
| Inhibition / therapeutic angle | SPC catalytic activity can be chemically inhibited by cavinafungin, which experimentally abolishes noncanonical SPC cleavage and is discussed as a way to perturb viral protein maturation and SPC-dependent processing. This is a catalytic SPC/SEC11 inhibitor, not an SPCS2-specific inhibitor, but it is directly relevant to SPCS2-containing complexes. (pqac-00000001, pqac-00000004, pqac-00000018) | Pharmacology; substrate-processing assays | Cavinafungin produced a “complete block” of Cx32/noncanonical cleavage in the cited human SPC quality-control work. (pqac-00000001, pqac-00000004, pqac-00000018) | Zanotti, 2023, https://doi.org/10.11588/heidok.00033417 |
| Disease / translational associations | Disease linkage for SPCS2 itself is presently indirect in the cited evidence: Open Targets lists modest disease associations including dengue disease (score 0.4629), neurodegenerative disease (0.5271), type 2 diabetes mellitus (0.2845), alcohol drinking (0.0527), and abruptio placentae (0.0483), but these appear evidence-aggregated rather than gene-specific mechanistic validation. In membrane-protein QC, SPC activity is relevant to disease-linked Cx32 mutants (>200 known variants reported for Cx32 in the cited thesis). (pqac-00000000, pqac-00000001) | Database aggregation; disease-substrate functional context | Open Targets evidence counts shown as 5 for each listed association; association scores: neurodegenerative disease 0.5271, dengue disease 0.4629, T2DM 0.2845, alcohol drinking 0.0527, abruptio placentae 0.0483. Cx32 noted to have >200 disease-linked variants. (pqac-00000000, pqac-00000001) | Open Targets context (pqac-00000000); Zanotti, 2023, https://doi.org/10.11588/heidok.00033417 |


*Table: This table summarizes the best-supported findings about human SPCS2 and the ER signal peptidase complex from the cited context. It highlights what is directly known for SPCS2 versus what is inferred from SPC-wide, structural, and comparative studies.*