Affinage

COG5

Conserved oligomeric Golgi complex subunit 5 · UniProt Q9UP83

Length
860 aa
Mass
94.9 kDa
Annotated
2026-06-09
18 papers in source corpus 9 papers cited in narrative 9 extracted findings
Cross-family judge faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

COG5 is a subunit of the conserved oligomeric Golgi (COG) tethering complex that controls vesicle trafficking through the Golgi and the localization of glycosylation machinery (PMID:11929878, PMID:16051600). Biochemical fractionation places COG5 in the lobe B (Cog5–7) subcomplex, where Cog8 bridges Cog5–7 to the Cog1–4 lobe to assemble the complete COG complex (PMID:16051600), and crystallographic analysis shows that COG5 adopts a CATCHR helical-rod fold and binds COG7 through an interface whose disruption impairs trafficking and glycosylation in human cells (PMID:25331899, PMID:38987656). Functionally, COG5 is required for retrograde intra-Golgi and Golgi-to-ER trafficking: loss of COG5 delays brefeldin-A–induced retrograde transport, a defect rescued by wild-type COG5, and produces dilated Golgi cisternae and glycoconjugate synthesis defects (PMID:16051600, PMID:19690088). Beyond glycosylation, COG5 deficiency fragments the Golgi and elevates PERK-driven ER stress signaling (PMID:33277529), and impairs mitochondrial complex I content through a copper-dependent disruption of iron-sulfur cluster function that is reversed by copper chelation or COG5 re-expression (PMID:41824529). A homozygous COG5 splicing mutation that severely reduces protein levels underlies a congenital disorder of glycosylation in patient fibroblasts (PMID:19690088).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2002 Medium

    Established that GTC-90/COG5 is a physical component of the mammalian COG complex, placing it in the machinery governing Golgi function and ER-to-Golgi transport.

    Evidence Reciprocal co-immunoprecipitation of COG5 with Sec34/COG2 and COG1 from rat liver cytosol plus semi-intact cell transport assays

    PMID:11929878

    Open questions at the time
    • Did not resolve subcomplex architecture or which transport step COG5 specifically supports
    • Direct molecular partners of COG5 within the complex not defined
  2. 2003 High

    Demonstrated a direct cellular requirement for COG5 in Golgi-dependent membrane delivery, linking trafficking to rapid expansion of cell surface area during cytokinesis and spermatid elongation.

    Evidence Loss-of-function mutants of the Drosophila homologue Fws with Golgi localization and cytokinesis/acroblast phenotypes

    PMID:12529436

    Open questions at the time
    • Cargo or vesicle class trafficked through COG5 not identified
    • Relationship to specific COG subcomplexes not addressed in this model
  3. 2005 High

    Defined the modular architecture of the COG complex and the functional consequence of COG5 loss for Golgi structure and glycosylation.

    Evidence RNAi knockdown in HeLa cells with gel filtration, immunoblotting, immunofluorescence and glycosylation/LDL receptor assays

    PMID:16051600

    Open questions at the time
    • Direct binding interfaces within the Cog5–7 lobe not resolved structurally
    • Distinctive subunit-specific roles only partially explained by GEAR sensitivity
  4. 2009 High

    Directly established COG5 as required for retrograde Golgi-to-ER trafficking and as a disease gene, via complementation of a patient defect.

    Evidence Brefeldin-A retrograde trafficking assay in patient fibroblasts carrying a homozygous splicing mutation, rescued by wild-type COG5 cDNA

    PMID:19690088

    Open questions at the time
    • Mechanistic step at which COG5 acts in retrograde transport not defined
    • Full clinical spectrum of COG5 deficiency not delineated
  5. 2014 High

    Provided the structural basis for COG5 function by showing it is a CATCHR-fold subunit that binds COG7 through a physiologically essential interface.

    Evidence X-ray crystallography of the Cog5–Cog7 complex with interface mutagenesis and trafficking/glycosylation assays in human cells

    PMID:25331899

    Open questions at the time
    • Structure of full assembled COG complex not resolved
    • How the Cog5–7 rod engages membranes or SNAREs not addressed
  6. 2020 Medium

    Extended COG5 function beyond glycosylation by linking its loss to PERK-mediated ER stress and downstream DNA damage.

    Evidence Golgi morphology imaging, PERK western blots, and DNA damage markers in patient-derived cells and murine retina

    PMID:33277529

    Open questions at the time
    • No direct rescue experiment to confirm causality of the PERK/DNA-damage axis
    • Mechanism linking Golgi fragmentation to PERK activation unresolved
  7. 2024 Medium

    Confirmed at single-variant resolution that disease-associated COG5 mutations act by destabilizing the protein and abrogating the COG5–COG7 interaction.

    Evidence Co-immunoprecipitation in patient-derived cells with a p.Leu100Phe variant plus in silico stability/solubility analysis

    PMID:38987656

    Open questions at the time
    • Solubility/stability claims rest partly on computational prediction
    • Quantitative effect on full complex assembly not measured
  8. 2026 High

    Connected COG5 function to mitochondrial bioenergetics, revealing a copper-dependent pathway by which COG5 loss impairs complex I assembly.

    Evidence Proteomics, OXPHOS biochemistry, copper measurements, and dual rescue (copper chelation and COG5 re-expression) in knockout and patient-derived cells

    PMID:41824529

    Open questions at the time
    • Molecular route by which COG5/Golgi dysfunction elevates cellular copper not defined
    • Link between copper and iron-sulfur cluster impairment not mechanistically dissected

Open questions

Synthesis pass · forward-looking unresolved questions
  • How a Golgi tethering defect propagates to ER stress, copper homeostasis, and mitochondrial complex I assembly within a single mechanistic chain remains unresolved.
  • No unified model linking trafficking loss to copper dysregulation
  • Direct cargo whose mistrafficking causes copper accumulation unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 3 GO:0005198 structural molecule activity 1
Localization
GO:0005794 Golgi apparatus 2
Pathway
R-HSA-5653656 Vesicle-mediated transport 3 R-HSA-392499 Metabolism of proteins 2
Partners
COG1COG2COG7COG8
Complex memberships
COG complexCog5-Cog7 subcomplex (lobe B)

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2002 COG5 (GTC-90) was co-immunoprecipitated with Sec34 (COG2) and ldlBp (COG1) from rat liver cytosol, establishing that GTC-90/COG5 is a component of the mammalian COG complex that regulates Golgi function and ER-to-Golgi transport. Large-scale immunoprecipitation of rat liver cytosol with anti-Sec34 antibodies; co-IP of epitope-tagged subunits in transfected cells; semi-intact cell transport assay with inhibitory antibodies The Journal of biological chemistry Medium 11929878
2003 The Drosophila COG5 homologue Fws (four way stop) localizes to Golgi structures and is required for cleavage furrow ingression during spermatocyte cytokinesis, cell elongation of differentiating spermatids, and assembly/stability of the Golgi-based acroblast, demonstrating a direct role for COG5 in vesicle trafficking through the Golgi to support rapid increases in cell surface area. Loss-of-function genetic mutants in Drosophila; immunofluorescence localization of Fws protein to Golgi; phenotypic analysis of cytokinesis and cell elongation defects Molecular biology of the cell High 12529436
2005 Cog5-deficient HeLa cells (generated by RNAi) showed dilated Golgi cisternae and glycosylation defects, demonstrating COG5's role in Golgi structure and glycoconjugate synthesis. Biochemical fractionation (gel filtration and immunoblotting) of COG-deficient cells established that Cog2–4 and Cog5–7 form stable subcomplexes, Cog8 associates with both Cog5–7 and Cog1–4, and Cog8 bridges the two lobes into the complete COG complex. Only one or two GEAR Golgi membrane proteins sensitive to Cog1/2 loss are also sensitive to Cog5 deficiency, indicating distinctive subunit roles. RNAi-mediated stable knockdown in HeLa cells; immunoblotting; gel filtration; immunofluorescence microscopy; glycosylation assays; LDL receptor processing assay The Journal of biological chemistry High 16051600
2009 A homozygous splicing mutation in COG5 (c.1669-15T>C) causing exon skipping and severely reduced COG5 protein expression markedly delayed retrograde Golgi-to-ER trafficking in patient fibroblasts upon brefeldin-A treatment, and this trafficking delay was rescued to normal by expressing wild-type COG5 cDNA, directly establishing COG5 as required for retrograde intra-Golgi/Golgi-to-ER trafficking. Brefeldin-A treatment of patient fibroblasts with quantification of retrograde trafficking; rescue by wild-type COG5 cDNA expression; serum glycoprotein analysis; sequencing Human molecular genetics High 19690088
2014 Crystal structure of the Cog5–Cog7 complex revealed that Cog5 belongs to the CATCHR (complexes associated with tethering containing helical rods) fold family, with structural homology to subunits of the Dsl1, exocyst, and GARP complexes. Biochemical and cell-based functional studies validated the physiological relevance of the Cog5–Cog7 interface and demonstrated that disruption of this interface in human cells causes defects in trafficking and glycosylation. X-ray crystallography; biochemical interaction assays; mutagenesis of the Cog5–Cog7 interface; functional assays in human cells (trafficking and glycosylation readouts) Proceedings of the National Academy of Sciences of the United States of America High 25331899
2020 COG5 variants in patient cells caused fragmentation of the Golgi apparatus and upregulation of the UPR kinase PERK; elevated PERK activity in turn induced DNA damage in cultured cells and in murine retina, identifying a role for COG5 in maintaining ER protein homeostasis beyond its canonical glycosylation function. Immunofluorescence of Golgi morphology in patient-derived cells; western blot quantification of PERK; DNA damage markers in cultured cells and murine retinal tissue Scientific reports Medium 33277529
2024 A missense variant (p.Leu100Phe) in COG5 altered protein solubility and stability and disrupted the COG5–COG7 protein interaction, as confirmed by co-immunoprecipitation in patient-derived cells where binding of COG5 to COG7 was abrogated. Co-immunoprecipitation from patient-derived cells; in silico stability/solubility analysis of COG5 variants Journal of human genetics Medium 38987656
2026 COG5 deficiency (in COG5-knockout and patient-derived cell models) impairs mitochondrial oxidative phosphorylation by reducing complex I content, and this impairment is linked to elevated cellular copper levels that disrupt mitochondrial iron-sulfur cluster function. Both restoration of COG5 expression and treatment with a copper chelator rescued the OXPHOS complex deficiency, establishing a copper-dependent pathway connecting COG5 function to mitochondrial complex I assembly. Proteomic analysis of COG5-deficient vs. rescue cell models; biochemical validation of OXPHOS complex content; copper level measurements; copper chelator rescue; COG5 re-expression rescue; patient-derived cells PLoS genetics High 41824529
2024 In yeast, all lobe B COG subunits (Cog5–Cog8) are required for resistance to the K28 A/B toxin, primarily because loss of COG complex function mislocalizes the endolysosomal defence factor Ktd1, rather than solely affecting surface glycosylation of K28-binding molecules. High-throughput K28 sensitivity assay in yeast cog mutants; fluorescence localization of Ktd1 in cog mutants; genetic epistasis with surface glycosylation mutants bioRxivpreprint Medium bio_10.1101_2024.12.20.629825

Source papers

Stage 0 corpus · 18 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2003 The Drosophila Cog5 homologue is required for cytokinesis, cell elongation, and assembly of specialized Golgi architecture during spermatogenesis. Molecular biology of the cell 104 12529436
2009 Deficiency in COG5 causes a moderate form of congenital disorders of glycosylation. Human molecular genetics 94 19690088
2005 Genetic analysis of the subunit organization and function of the conserved oligomeric golgi (COG) complex: studies of COG5- and COG7-deficient mammalian cells. The Journal of biological chemistry 74 16051600
2012 COG5-CDG: expanding the clinical spectrum. Orphanet journal of rare diseases 38 23228021
2011 COG5-CDG with a Mild Neurohepatic Presentation. JIMD reports 33 23430875
2010 Fusion of HMGA2 to COG5 in uterine leiomyoma. Cancer genetics and cytogenetics 29 20804914
2002 Sec34 is implicated in traffic from the endoplasmic reticulum to the Golgi and exists in a complex with GTC-90 and ldlBp. The Journal of biological chemistry 23 11929878
2014 Cog5-Cog7 crystal structure reveals interactions essential for the function of a multisubunit tethering complex. Proceedings of the National Academy of Sciences of the United States of America 20 25331899
2020 Identification of Two Novel Mutations in COG5 Causing Congenital Disorder of Glycosylation. Frontiers in genetics 16 32174980
2020 Fetal glycosylation defect due to ALG3 and COG5 variants detected via amniocentesis: Complex glycosylation defect with embryonic lethal phenotype. Molecular genetics and metabolism 12 33187827
2017 A Mild Form of COG5 Defect Showing Early-Childhood-Onset Friedreich's-Ataxia-Like Phenotypes with Isolated Cerebellar Atrophy. Journal of Korean medical science 12 28960046
2019 Novel compound heterozygous COG5 mutations in a Chinese male patient with severe clinical symptoms and type IIi congenital disorder of glycosylation: A case report. Experimental and therapeutic medicine 8 31572517
2020 COG5 variants lead to complex early onset retinal degeneration, upregulation of PERK and DNA damage. Scientific reports 6 33277529
2023 The First Congenital Disorders of Glycosylation Patient (Fetus) with Homozygous COG5 c.95T>G Variant. Molecular syndromology 2 37064333
2024 Novel mutation of COG5 in a Taiwanese girl with congenital disorders of glycosylation manifesting as developmental delay. Molecular genetics and metabolism reports 1 38559322
2026 COG5 deficiency disrupts cellular copper homeostasis and underlies the impaired mitochondrial OXPHOS function. PLoS genetics 0 41824529
2026 Novel Compound Heterozygous Variants in the COG5 Gene Causing Fetal Hydrops and Skeletal Dysplasia. Molecular genetics & genomic medicine 0 41952427
2024 Characterization of a missense variant in COG5 in a Tunisian patient with COG5-CDG syndrome and insights into the effect of non-synonymous variants on COG5 protein. Journal of human genetics 0 38987656

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