Affinage

PRAF2

PRA1 family protein 2 · UniProt O60831

Length
178 aa
Mass
19.3 kDa
Annotated
2026-06-10
17 papers in source corpus 8 papers cited in narrative 8 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 4/4 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PRAF2 is an ER-resident four-transmembrane protein that functions as a gatekeeper controlling the biosynthetic export of polytopic plasma membrane proteins, retaining them in the ER until they are properly assembled (PMID:26645984, PMID:36167862, PMID:38139265). It binds newly synthesized client receptors and transporters through transmembrane-domain contacts and prevents their recruitment into COPII vesicles at ER exit sites: it retains the GABAB receptor GB1 subunit in the absence of GB2 heterodimerization (PMID:26645984), stoichiometrically holds both wild-type and F508del CFTR away from ER exit sites such that pharmacological chaperones act in part by relieving this retention (PMID:36167862), and limits CCR5 plasma membrane export through transmembrane-domain interaction, an effect opposed by the CCR5 escort protein CD4 (PMID:38139265). Beyond its trafficking role, PRAF2 has a pro-apoptotic activity: its overexpression drives Bax translocation to mitochondria and cell death, an activity suppressed by interaction with the transmembrane domains of the anti-apoptotic proteins Bcl-xL and Bcl-2 (PMID:21203533). PRAF2 localizes principally to the ER, co-localizing with calnexin, and also distributes to Golgi, cytoplasmic vesicular puncta, and additional neuronal compartments, consistent with its trafficking and Rab-acceptor-associated functions (PMID:15757671, PMID:26645984).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2005 Medium

    Established PRAF2 as a four-transmembrane protein physically associated with a GPCR (CCR5) and resident in the early secretory pathway, framing it as a candidate trafficking regulator.

    Evidence Co-IP, immunofluorescence co-localization with calnexin and M6P receptor, and two-hybrid screen in cell lines

    PMID:15757671

    Open questions at the time
    • No functional consequence of the CCR5 interaction shown
    • Rab-acceptor motif function not tested directly
    • Heterodimerization with JWA/GTRAP3-18 not mechanistically dissected
  2. 2010 High

    Defined a pro-apoptotic activity for PRAF2 that is gated by anti-apoptotic Bcl-family proteins, linking the protein to mitochondrial death control.

    Evidence TAP/Co-IP, domain-deletion mutagenesis of Bcl-xL, Bax translocation assay, and overexpression/knockdown apoptosis readouts in U2OS cells

    PMID:21203533

    Open questions at the time
    • Molecular mechanism by which PRAF2 promotes Bax translocation is unresolved
    • Whether the ER-trafficking role and apoptotic role are mechanistically connected is unknown
  3. 2010 Medium

    Tied PRAF2 expression to cancer-cell viability and motility, with monomeric versus dimeric forms partitioning to distinct compartments.

    Evidence Immunofluorescence, cell fractionation, RNAi, and migration/invasion assays in U-87 glioma cells

    PMID:20412121

    Open questions at the time
    • Functional difference between monomer and dimer not defined
    • Mechanism linking PRAF2 to invasion not established
  4. 2015 Medium

    Identified the core gatekeeper function: PRAF2 retains the GABAB GB1 subunit in the biosynthetic pathway until heterodimerization with GB2.

    Evidence Immunofluorescence and ultrastructural immunocytochemistry (electron microscopy) in mouse CNS neurons

    PMID:26645984

    Open questions at the time
    • Mechanism of release upon GB2 assembly not detailed
    • Functional roles of mitochondrial and primary cilia localizations unexplored
  5. 2019 Low

    Extended PRAF2 function to exosome-mediated cargo release relevant to cancer metastasis.

    Evidence siRNA knockdown, transcriptome microarray, and exosome isolation/functional assays in colorectal cancer cells

    PMID:31198409

    Open questions at the time
    • Indirect evidence without direct mechanistic dissection of PRAF2 in exosome biogenesis
    • Whether effect is direct or secondary to trafficking changes is unclear
  6. 2022 High

    Demonstrated that PRAF2 acts at COPII exit sites by stoichiometrically retaining CFTR, including the F508del mutant, providing a disease-relevant mechanism for pharmacological chaperone action.

    Evidence Stoichiometric Co-IP, COPII vesicle budding assay, and pharmacological chaperone treatment

    PMID:36167862

    Open questions at the time
    • Determinants of client selectivity not defined
    • How chaperones relieve PRAF2 retention mechanistically not resolved
  7. 2023 High

    Resolved the molecular logic of PRAF2 client retention versus escort: transmembrane-domain interaction drives retention, opposed by the client-specific escort CD4 at ER exit sites.

    Evidence BRET subcellular localization and proximity assays, Co-IP, and domain mutagenesis of CCR5

    PMID:38139265

    Open questions at the time
    • General rules governing which escort proteins counteract PRAF2 are unknown
    • Structural basis of the transmembrane-domain contact not determined

Open questions

Synthesis pass · forward-looking unresolved questions
  • How PRAF2's ER-gatekeeper trafficking activity and its Bcl-family-gated pro-apoptotic activity are mechanistically integrated remains unresolved.
  • No structural model of PRAF2 or its transmembrane-domain client interactions
  • No unifying mechanism linking COPII retention to Bax-dependent apoptosis
  • Functional significance of mitochondrial and ciliary localizations uncharacterized

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3 GO:0140313 molecular sequestering activity 3
Localization
GO:0005783 endoplasmic reticulum 3 GO:0031410 cytoplasmic vesicle 2 GO:0005739 mitochondrion 1 GO:0005794 Golgi apparatus 1 GO:0005929 cilium 1
Pathway
R-HSA-9609507 Protein localization 3 R-HSA-5653656 Vesicle-mediated transport 2 R-HSA-5357801 Programmed Cell Death 1
Partners
BCL2BCL2L1CCR5CD4CFTRGABBR1

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 PRAF2 (JM4) is a four-transmembrane protein that physically interacts with (co-precipitates with) the CCR5 chemokine receptor. It co-localizes with calnexin in the endoplasmic reticulum and with the mannose 6-phosphate receptor in the Golgi. PRAF2 also heterodimerizes with the related proteins JWA and GTRAP3-18, and harbors a Rab-acceptor motif, suggesting a function in vesicle formation at the Golgi complex. Co-immunoprecipitation, co-localization by immunofluorescence microscopy, two-hybrid interaction screen FEBS letters Medium 15757671
2007 PRAF2 protein localizes in bright cytoplasmic punctae in neuroblastoma cells (consistent with vesicular/ER-Golgi compartments), and its protein levels increase during cerulenin-induced apoptosis. Immunofluorescence microscopy, Annexin V staining, PARP cleavage assay Clinical cancer research Low 17975142
2010 PRAF2 interacts with Bcl-xL, and this interaction depends on the transmembrane domain of Bcl-xL. PRAF2 also interacts with Bcl-2. Overexpression of PRAF2 induces translocation of Bax to mitochondria and apoptotic cell death; this death is prevented by co-transfection of Bcl-xL but not by a transmembrane-domain-deleted mutant of Bcl-xL. Knockdown of PRAF2 increases clonogenicity of U2OS cells after etoposide treatment by reducing cell death. Tandem affinity purification (TAP), Co-IP, overexpression/knockdown with apoptosis readouts (Annexin V, caspase), Bax mitochondrial translocation assay, domain-deletion mutagenesis PloS one High 21203533
2010 PRAF2 protein is detected in small vesicle-like structures throughout the cytoplasm and in/around cell nuclei of malignant glioma cells. Monomeric and dimeric forms of PRAF2 associate with different subcellular compartments. RNAi-mediated knockdown of PRAF2 significantly reduces cell viability, migration, and invasiveness of U-87 glioma cells. Immunofluorescence microscopy, cell fractionation, RNA interference, migration/invasion assays Cancer science Medium 20412121
2015 Ultrastructural and immunocytochemical analysis confirmed PRAF2 localization primarily in the ER of neurons, but also revealed previously unrecognized localizations in mitochondria, primary cilia, and the sub-synaptic region of mouse CNS. PRAF2 acts as a gatekeeper for the GABAB receptor GB1 subunit, preventing its progression through the biosynthetic pathway in the absence of heterodimerization with GB2. Immunofluorescence microscopy, electron microscopy (ultrastructural immunocytochemistry) Brain structure & function Medium 26645984
2019 JAG2-rich exosomes are released from colorectal cancer cells in a PRAF2-dependent manner, and these exosomes regulate metastasis of colorectal cancer cells in a paracrine manner, indicating PRAF2 has a role in exosome-mediated cargo trafficking. siRNA knockdown, transcriptome microarray, exosome isolation and functional assays Cancer cell international Low 31198409
2022 PRAF2, an ER-resident gatekeeper, interacts stoichiometrically with both wild-type CFTR and the CF mutant CFTR-F508del, preventing newly synthesized CFTR from accessing ER exit sites (COPII vesicle recruitment). Because of its lower abundance, CFTR-F508del recruitment into COPII vesicles is suppressed by PRAF2. Pharmacological chaperones that rescue CFTR-F508del function in CF patients act at least partly by targeting CFTR-F508del retention by PRAF2. Co-immunoprecipitation, COPII vesicle budding assay, pharmacological chaperone treatment, proximity/co-localization assays Cellular and molecular life sciences : CMLS High 36167862
2023 PRAF2 inhibits CCR5 plasma membrane export in a concentration-dependent manner. PRAF2/CCR5 interaction does not require the CCR5 C-terminal tail but instead involves the transmembrane domains of both proteins. The di-leucine/RXR motif in the third intracellular loop of CCR5 does not affect PRAF2-mediated retention; rather, it impairs CCR5 interaction with its private escort protein CD4. PRAF2 and CD4 exert opposing effects on CCR5 cell-surface export, likely by regulating CCR5 recruitment into COPII vesicles at ER exit sites. BRET-based subcellular localization assay, BRET proximity assay, Co-immunoprecipitation, domain mutation analysis International journal of molecular sciences High 38139265

Source papers

Stage 0 corpus · 17 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2019 Long non-coding RNA HOTAIR functions as a competitive endogenous RNA to regulate PRAF2 expression by sponging miR-326 in cutaneous squamous cell carcinoma. Cancer cell international 45 31649487
2005 JM4 is a four-transmembrane protein binding to the CCR5 receptor. FEBS letters 44 15757671
2010 Praf2 is a novel Bcl-xL/Bcl-2 interacting protein with the ability to modulate survival of cancer cells. PloS one 36 21203533
2007 Expression of prenylated Rab acceptor 1 domain family, member 2 (PRAF2) in neuroblastoma: correlation with clinical features, cellular localization, and cerulenin-mediated apoptosis regulation. Clinical cancer research : an official journal of the American Association for Cancer Research 23 17975142
2010 Subcellular distribution and expression of prenylated Rab acceptor 1 domain family, member 2 (PRAF2) in malignant glioma: Influence on cell survival and migration. Cancer science 22 20412121
2019 Mutual regulation of JAG2 and PRAF2 promotes migration and invasion of colorectal cancer cells uncoupled from epithelial-mesenchymal transition. Cancer cell international 14 31198409
2016 The Glycosylphosphatidylinositol-Anchored Variable Region of Llama Heavy Chain-Only Antibody JM4 Efficiently Blocks both Cell-Free and T Cell-T Cell Transmission of Human Immunodeficiency Virus Type 1. Journal of virology 14 27654286
2020 JHDM1D-AS1 aggravates the development of gastric cancer through miR-450a-2-3p-PRAF2 axis. Life sciences 13 33245963
2006 Genetics of subpeptin JM4-A and subpeptin JM4-B production by Bacillus subtilis JM4. Biochemical and biophysical research communications 12 16647040
2020 Prolonged Beneficial Effect of Brief Erythropoietin Peptide JM4 Therapy on Chronic Relapsing EAE. Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics 10 32959273
2021 Grape Seed Proanthocyanidins (GSPs) Inhibit the Development of Cutaneous Squamous Cell Carcinoma by Regulating the hsa_circ_0070934/miR-136-5p/PRAF2 Axis. Cancer management and research 9 34103991
2022 PRAF2 is an oncogene acting to promote the proliferation and invasion of breast cancer cells. Experimental and therapeutic medicine 7 36478884
2018 PRAF2 expression indicates unfavorable clinical outcome in hepatocellular carcinoma. Cancer management and research 7 30100755
2022 Pharmacological chaperone-rescued cystic fibrosis CFTR-F508del mutant overcomes PRAF2-gated access to endoplasmic reticulum exit sites. Cellular and molecular life sciences : CMLS 4 36167862
2015 Anatomical and ultrastructural study of PRAF2 expression in the mouse central nervous system. Brain structure & function 4 26645984
2023 Control of CCR5 Cell-Surface Targeting by the PRAF2 Gatekeeper. International journal of molecular sciences 1 38139265
2025 PRAF2 as a novel biomarker for breast cancer with machine learning and experimentation validation. BMC cancer 0 39773456

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