SRPRB (signal recognition particle receptor subunit beta, SR-beta; also APMCF1) is a 271 aa single-pass ER membrane protein and a small Ras-superfamily GTPase closely related to Arf and Sar1. It is the membrane-anchored beta subunit of the heterodimeric signal recognition particle (SRP) receptor (SR), assembling with the soluble alpha subunit SRPRA via a Longin-domain interface and tethering SRPRA to the ER membrane. The SRP receptor docks the SRP-ribosome-nascent chain complex at the ER so that signal-sequence-bearing nascent secretory and membrane proteins are delivered to the Sec61 translocon for cotranslational translocation and insertion. SRP-dependent targeting is driven by a GTPase cycle in which the SR (SRPRA and SRPRB) and the SRP54 GTPase reciprocally activate one another; GTP binding and hydrolysis by SRPRB regulate ribosome-nascent chain handover and receptor recycling. SRPRB is broadly expressed and localizes to the ER membrane.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005785 signal recognition particle receptor complex | IBA GO_REF:0000033 | ACCEPT | Summary: SRPRB is the beta subunit of the heterodimeric SRP receptor; phylogenetic assignment of SR-complex membership is consistent with direct structural and biochemical evidence. Core structural identity. Reason: SRP receptor complex membership is the core cellular-component identity of SRPRB; SRPRB heterodimerizes with SRPRA. Supporting Evidence: file:human/SRPRB/SRPRB-uniprot.txt Component of the signal recognition particle (SRP) complex receptor (SR) |
| GO:0045047 protein targeting to ER | IBA GO_REF:0000033 | ACCEPT | Summary: As part of the SRP receptor, SRPRB participates in targeting nascent secretory/membrane proteins to the ER. Core biological process. Reason: Core SR-mediated process; the SRP receptor ensures correct targeting of nascent proteins to the ER membrane. Supporting Evidence: file:human/SRPRB/SRPRB-uniprot.txt the correct targeting of the nascent secretory proteins to the |
| GO:0005525 GTP binding | IEA GO_REF:0000002 | ACCEPT | Summary: SRPRB is a small GTPase of the Ras superfamily (Arf/Sar1-related) with conserved GTP-binding motifs; GTP binding and hydrolysis drive the SRP-targeting cycle. Core molecular function. Reason: Core molecular function; SRPRB binds GTP (structure solved in the Mg2+-GTP-bound state) and its GTPase activity regulates targeting. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Electronic transfer of the ER membrane subcellular location from UniProt; the correct and core compartment for the membrane-anchored SR-beta subunit. Reason: Correct core location; SRPRB is a single-pass ER membrane protein. Supporting Evidence: file:human/SRPRB/SRPRB-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005515 protein binding | IPI PMID:16169070 A human protein-protein interaction network: a resource for ... | KEEP AS NON CORE | Summary: High-throughput protein-protein interaction capture. SRPRB's functionally informative interaction is with SRPRA (the SR heterodimer), but bare protein binding is uninformative. Reason: Real but the bare protein binding term is uninformative per curation guidelines; the SR-complex term captures the informative content. Supporting Evidence: file:human/SRPRB/SRPRB-uniprot.txt Heterodimer with SRPRA |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | KEEP AS NON CORE | Summary: BioPlex affinity-MS interactome capture. Bare protein binding is uninformative. Reason: High-throughput interaction; bare protein binding is uninformative and not core. Supporting Evidence: file:human/SRPRB/SRPRB-uniprot.txt Heterodimer with SRPRA |
| GO:0005515 protein binding | IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func... | KEEP AS NON CORE | Summary: Multimodal cell-map interactome capture. Bare protein binding is uninformative. Reason: High-throughput interaction; bare protein binding is uninformative and not core. Supporting Evidence: file:human/SRPRB/SRPRB-uniprot.txt Heterodimer with SRPRA |
| GO:0005785 signal recognition particle receptor complex | EXP PMID:16439358 The structure of the mammalian signal recognition particle (... | ACCEPT | Summary: Crystal structure of mammalian SR-beta in complex with the SRalpha (SRPRA) binding domain (SRX); direct experimental evidence that SRPRB is part of the heterodimeric SRP receptor. Core structural identity. Reason: Experimentally demonstrated core SR membership; SRPRB-SRPRA heterodimer structure. Supporting Evidence: PMID:16439358 The SR is a heterodimeric complex assembled by the two GTPases SRalpha and SRbeta |
| GO:0006617 SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition | NAS PMID:16439358 The structure of the mammalian signal recognition particle (... | ACCEPT | Summary: SRPRB, as part of the SR, participates in SRP-dependent cotranslational targeting of nascent chains to the ER membrane. Core biological process. Reason: Core SR-mediated process; the SRP receptor mediates SRP-dependent cotranslational targeting at the ER. Supporting Evidence: PMID:16439358 co-translational targeting of secretory and membrane proteins to the endoplasmic reticulum |
| GO:0016020 membrane | NAS PMID:16439358 The structure of the mammalian signal recognition particle (... | KEEP AS NON CORE | Summary: The SR is membrane-anchored via SRPRB; a generic membrane localization that is a parent of the specific ER membrane term. Reason: Correct but generic; the ER membrane term captures the informative localization. Supporting Evidence: PMID:16439358 which is membrane-anchored |
| GO:0005789 endoplasmic reticulum membrane | ISS GO_REF:0000024 | ACCEPT | Summary: Curator ISS transfer of ER membrane localization from an ortholog; the correct and core compartment for SRPRB. Reason: Correct core location; redundant with other ER membrane evidence. Supporting Evidence: file:human/SRPRB/SRPRB-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0016020 membrane | IDA PMID:22375059 Different effects of Sec61Ξ±, Sec62 and Sec63 depletion on tr... | KEEP AS NON CORE | Summary: Direct evidence of membrane localization from a study of Sec61/Sec62/Sec63-dependent ER translocation; a generic membrane term, parent of ER membrane. Reason: Correct but generic; the ER membrane term captures the informative localization. Supporting Evidence: file:human/SRPRB/SRPRB-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005789 endoplasmic reticulum membrane | TAS Reactome:R-HSA-1791060 | ACCEPT | Summary: Reactome TAS annotation of ER membrane localization for SRPRB, consistent with the core compartment. Reason: Correct core location; consistent with experimental and ISS evidence. Supporting Evidence: file:human/SRPRB/SRPRB-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005881 cytoplasmic microtubule | IDA PMID:23264731 MTR120/KIAA1383, a novel microtubule-associated protein, pro... | REMOVE | Summary: Wrong-gene citation. PMID:23264731 characterizes MTR120/KIAA1383 as a microtubule-associated protein; the now-cached full text never mentions or assays SRPRB (no occurrence of SRPRB / SR-beta / SRP receptor). SRPRB is an ER-membrane GTPase, for which a cytoplasmic microtubule localization is biologically implausible. Reason: The full text of PMID:23264731 is now available and confirms the paper is entirely about MTR120/KIAA1383 and does not assay SRPRB, so this GO:0005881 IDA is a wrong-gene mis-attribution. This matches the sibling SERP1 review, where the same PMID:23264731 cytoplasmic-microtubule annotation was REMOVED after full-text confirmation; previously this row was held UNDECIDED only because the full text was unavailable. Supporting Evidence: PMID:23264731 a novel microtubule-associated protein, promotes microtubule stability and ensures cytokinesis |
| GO:0005737 cytoplasm | IDA PMID:19664239 Subcellular localization of APMCF1 and its biological signif... | KEEP AS NON CORE | Summary: GFP-APMCF1 (SRPRB) overexpression showed a generally cytoplasmic distribution in COS-7 cells. A diffuse cytoplasmic signal is consistent with an ER-membrane protein (the ER is in the cytoplasm), but cytoplasm is imprecise relative to the ER membrane and the signal derives from overexpression of a GFP fusion. Reason: Plausible but imprecise (and overexpression-based); the informative core localization is the ER membrane. Supporting Evidence: PMID:19664239 EGFP-APMCF1 was generally localized in the cytoplasm of COS-7 cell |
Loading supporting contentβ¦
Download this section (compressed HTML)Q: Is the reported cytoplasmic-microtubule localization of SRPRB a genuine secondary localization or a mis-attribution from the MTR120 study, and does SRPRB have any verified function outside the SRP receptor?
Q: How do the GTPase cycles of SRPRB, SRPRA, and SRP54 coordinate ribosome-nascent chain handover to the Sec61 translocon, and what is the specific catalytic contribution of SRPRB GTP hydrolysis?
Experiment: Use endogenous tagging plus proximity labeling and super-resolution microscopy to test whether SRPRB localizes to microtubules under any condition, distinguishing genuine localization from overexpression or co-purification artifacts.
Experiment: Reconstitute SRP-dependent targeting with wild-type and GTPase-dead SRPRB to quantify the role of SRPRB GTP hydrolysis in receptor recycling and nascent-chain delivery to Sec61.
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)