| Topic | Summary | Quantitative data | Best citation IDs |
|---|---|---:|---|
| Identity / verified target | **SPCS3** in human corresponds to **signal peptidase complex subunit 3**, also called **SPC22/23**; it is an accessory/non-proteolytic SPC subunit present in both human SPC paralogs with SEC11A or SEC11C. | Human SPC resolved as ~**84 kDa** hetero-tetrameric complex; two paralogs: **SPC-A** and **SPC-C**. | (pqac-00000000, pqac-00000004, pqac-00000005) |
| Core function in SPC | SPCS3 forms part of the functional core of the ER signal peptidase complex, supporting cleavage of N-terminal signal peptides from secretory and membrane protein precursors by stabilizing and positioning the SEC11 catalytic center rather than acting as the catalytic serine protease itself. | Human secretome/translocome estimate discussed as **>3,000** signal peptides requiring SPC processing. | (pqac-00000005, pqac-00000006, pqac-00000010) |
| Localization / topology | ER-resident membrane complex; SPCS3 has a **luminal beta-sandwich (ASF1-like)** domain that embraces SEC11 and TM helices that contribute to the SPC transmembrane window at the **luminal membrane interface**. | SPCS3 is highly **N-glycosylated at Asp141 (~98%)** in the HEK293-derived sample described. | (pqac-00000002, pqac-00000004, pqac-00000019) |
| Mechanistic insight: TM window and membrane thinning | All SPC subunits collectively form a lipid-filled **TM window**; inner lining includes essential subunits **SEC11A/C and SPCS3**. Local ER bilayer thinning near the active site acts as a physical selector for signal peptides. | Average local membrane thinning in simulations: **~26%**; TM window width: **~15 Å**. | (pqac-00000005, pqac-00000008, pqac-00000019) |
| Mechanistic insight: signal peptide selectivity | SPC specificity is explained by a molecular-ruler mechanism: short signal-peptide h-regions can enter the thinned TM window and access the c-region pocket, whereas longer TM helices are excluded. | Mean SP h-region length: **11 residues**; SPC generally cannot cleave h-regions **>18–20 aa**. | (pqac-00000008, pqac-00000019) |
| 2023 advance: membrane-protein quality control model | A 2023 characterization proposed that SPC also performs **noncanonical, post-translocational quality-control cleavage** of multipass membrane proteins with exposed cryptic sites. In this model, **SPCS1** is the key recruitment or exosite factor, while **SEC11A/C + SPCS3** form the catalytic core. | Proteome-wide prediction of **~1,500** membrane proteins with cryptic SPC cleavage sites; validated substrates included connexins, iRhom2, and Hrd1. | (pqac-00000033, pqac-00000034, pqac-00000040) |
| 2024 finding: CHIKV interaction / host restriction | In human macrophage models, **SPCS3** was identified as a **CHIKV E1-binding host factor** with **anti-CHIKV** activity; overexpression did not alter CHIKV poly-glycoprotein cleavage, implying a **peptidase-independent** antiviral role. E1 residue **V220** helps the virus evade SPCS3 and eIF3k restriction. | Highly infected primary macrophage subset reported at **0.76%** at 24 h.p.i.; siRNA comparisons involving SPCS3 reached **p < 0.0001** in knockdown validation context. | (pqac-00000011, pqac-00000012, pqac-00000013, pqac-00000017) |
| 2024 finding: HCV and flavivirus interactomes | 2024 HCV interactomics placed SPC components near viral envelope and assembly proteins; **SPCS3** appeared in the **E2 accessory interactome**, while prior work cited in the paper linked **SPCS1/SPCS3** to flavivirus and HCV particle production. | SPCS3 transcript abundance in the HCV study table: **RPKM ~12.01**; SPCS2: **~34.69**; interactome statistics included **n = 3–4** for normalized IBAQ boxplots. | (pqac-00000030, pqac-00000031, pqac-00000032) |
| Translational relevance: ER-targeted antivirals affecting SPC-dependent biology | Recent flavivirus review highlights host-directed inhibition of ER translocation and signal peptide processing as a practical application area; although not SPCS3-selective, these compounds exploit the same ER biogenesis pathway in which SPCS3 functions. | **Cavinafungin** IC50s: **0.004 µM** (DENV1), **0.005 µM** (DENV2), **0.003 µM** (DENV3), **0.003 µM** (DENV4); **Apratoxin S4**: **0.003 µM** (DENV2, Huh7.5); **Cotransin 8** active at **0.5 µM** (Huh7 + C6/36) and **0.1–0.5 µM** (MDDCs); **PS3061** active at **1 µM**. | (pqac-00000024, pqac-00000025, pqac-00000026) |


*Table: This table condenses the most important validated information about human SPCS3/SPC22/23, including identity, ER localization, signal peptidase mechanism, recent 2023-2024 functional findings, and quantitative values relevant to annotation and translational interpretation.*