| 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. (pqac-00000001, pqac-00000019) | 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 (pqac-00000000) |
| 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. (pqac-00000001, pqac-00000019, pqac-00000021, pqac-00000025) | 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. (pqac-00000001, pqac-00000006, pqac-00000019) | 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. (pqac-00000001, pqac-00000017, pqac-00000019) | 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. (pqac-00000001, pqac-00000019, pqac-00000025) | 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. (pqac-00000017, pqac-00000019, pqac-00000021) | 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. (pqac-00000002, pqac-00000003, pqac-00000004, pqac-00000018, pqac-00000020, pqac-00000023) | 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**. (pqac-00000006, pqac-00000018, pqac-00000020) | 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**. (pqac-00000011, pqac-00000013, pqac-00000016) | 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. (pqac-00000009, pqac-00000010, pqac-00000015) | 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. (pqac-00000000) | 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 (pqac-00000000) |


*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.*