Affinage

COG5

Conserved oligomeric Golgi complex subunit 5 · UniProt Q9UP83

Length
860 aa
Mass
94.9 kDa
Annotated
2026-04-28
18 papers in source corpus 9 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

COG5 is a lobe B subunit of the conserved oligomeric Golgi (COG) tethering complex that maintains Golgi structure and function by mediating retrograde intra-Golgi and ER-to-Golgi vesicle trafficking, thereby ensuring proper glycosylation of secretory cargo. COG5 adopts a CATCHR (complexes associated with tethering containing helical rods) fold and forms a stable subcomplex with COG7 via a conserved interface whose disruption impairs Golgi trafficking and glycosylation (PMID:25331899, PMID:16051600). Beyond its canonical Golgi tethering role, COG5 deficiency elevates cellular copper levels, disrupting mitochondrial iron–sulfur cluster function and complex I assembly—defects rescuable by COG5 re-expression or copper chelation—and triggers Golgi fragmentation with UPR/PERK activation and downstream DNA damage (PMID:41824529, PMID:33277529). Loss-of-function mutations in COG5 cause a congenital disorder of glycosylation (CDG) characterized by defective N- and O-glycan sialylation, confirmed by functional rescue with wild-type COG5 cDNA in patient fibroblasts (PMID:19690088).

Mechanistic history

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

    Establishing that the COG complex participates in ER-to-Golgi transport answered whether this tethering complex functions only in intra-Golgi recycling or also in anterograde traffic from the ER.

    Evidence Neutralizing anti-Sec34 antibodies inhibited VSVG transport in a semi-intact cell assay; co-IP and in vitro binding identified COG subunit interactions

    PMID:11929878

    Open questions at the time
    • Specific contribution of COG5 versus other subunits to ER-to-Golgi tethering was not resolved
    • In vitro transport reconstitution with purified COG complex not performed
  2. 2003 High

    Demonstration that the Drosophila COG5 orthologue Fws is required for Golgi-dependent membrane remodeling during cytokinesis and spermatid elongation revealed that COG5 function extends beyond steady-state trafficking to rapid membrane expansion events.

    Evidence Loss-of-function mutant analysis with immunofluorescence localization in Drosophila spermatocytes and spermatids

    PMID:12529436

    Open questions at the time
    • Whether mammalian COG5 has analogous roles in cytokinesis was not tested
    • Vesicle cargo identity at the cleavage furrow unknown
  3. 2005 High

    Mapping COG5 to a stable lobe B subcomplex (COG5–6–7) bridged to lobe A by COG8 defined the modular architecture of the COG complex and showed that lobe B loss produces milder glycosylation defects than lobe A loss.

    Evidence siRNA knockdown in HeLa cells combined with gel filtration, immunoblotting, and glycosylation analysis compared to Cog1/Cog2 null CHO cells

    PMID:16051600

    Open questions at the time
    • Structural basis of the COG5–COG6 interaction within lobe B remained unresolved
    • Functional redundancy among lobe B subunits not fully tested
  4. 2009 High

    Identification of a COG5 splicing mutation in a CDG patient with defective retrograde Golgi trafficking, rescuable by wild-type COG5 re-expression, established COG5 as a disease gene and directly linked its function to glycosylation homeostasis in humans.

    Evidence Brefeldin-A trafficking assay in patient fibroblasts, serum glycoprotein profiling, and genetic rescue

    PMID:19690088

    Open questions at the time
    • Mechanism by which partial COG5 loss selectively affects sialylation over other glycosylation steps unclear
    • Neurological pathogenesis not mechanistically explained
  5. 2014 High

    The crystal structure of the COG5–COG7 complex revealed a CATCHR fold for COG5 and showed that the conserved COG5–COG7 interface is essential for Golgi trafficking, unifying COG with other CATCHR tethering complexes structurally.

    Evidence X-ray crystallography, interface-disrupting mutagenesis with functional assays in human cells

    PMID:25331899

    Open questions at the time
    • Full-length COG5 structure not obtained
    • How COG5 engages SNARE or Rab proteins was not resolved
  6. 2020 Medium

    Discovery that COG5 variants cause Golgi fragmentation and PERK-mediated UPR activation leading to DNA damage expanded the downstream consequences of COG5 dysfunction beyond glycosylation to ER proteostasis and genome integrity.

    Evidence Patient-derived cells and murine retina analyzed by immunofluorescence, western blot for PERK and DNA damage markers

    PMID:33277529

    Open questions at the time
    • Causal chain from Golgi fragmentation to PERK activation not mechanistically dissected
    • Whether UPR activation is specific to COG5 or general to COG deficiency unknown
    • Single-lab study
  7. 2024 Medium

    Characterization of the COG5 p.Leu100Phe variant showed that a single missense mutation can destabilize the protein and abolish the COG5–COG7 interaction, linking patient pathology to disruption of this specific subunit interface.

    Evidence Co-immunoprecipitation in patient-derived cells with in silico structural analysis

    PMID:38987656

    Open questions at the time
    • Single co-IP without reciprocal validation
    • Protein stability quantification was computational, not biophysical
    • Rescue experiment not performed
  8. 2026 High

    Revealing that COG5 deficiency elevates cellular copper, disrupts iron–sulfur cluster function and mitochondrial complex I assembly—rescuable by copper chelation—uncovered an unexpected link between Golgi tethering and mitochondrial bioenergetics via copper homeostasis.

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

    PMID:41824529

    Open questions at the time
    • Identity of the copper transporter(s) mis-trafficked upon COG5 loss not determined
    • Whether copper dysregulation is common to all COG subunit deficiencies unclear
    • In vivo validation in animal models not reported

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key open questions include how COG5 engages SNARE and Rab machinery to specify vesicle tethering, whether COG5's roles in copper homeostasis and UPR activation are shared by all lobe B subunits, and which copper transporter(s) are mis-trafficked when COG5 is lost.
  • SNARE/Rab binding interfaces on COG5 unresolved
  • Tissue-specific phenotypic mechanisms (e.g., neurodegeneration) not dissected
  • Full-length structural context of COG5 within the intact octameric complex lacking

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 2
Localization
GO:0005794 Golgi apparatus 5
Pathway
R-HSA-5653656 Vesicle-mediated transport 4 R-HSA-1643685 Disease 2 R-HSA-392499 Metabolism of proteins 2
Partners
COG1COG6COG7COG8
Complex memberships
COG complex (lobe B)

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 Drosophila Cog5 homologue (Fws) localizes to Golgi structures throughout spermatogenesis and is required for cleavage furrow ingression during spermatocyte cytokinesis, cell elongation in spermatids, and assembly of the Golgi-based acroblast, consistent with a role in facilitating vesicle traffic through the Golgi to support rapid increases in cell surface area. Loss-of-function genetic analysis, immunofluorescence localization, phenotypic analysis of dividing spermatocytes and differentiating spermatids Molecular biology of the cell High 12529436
2002 Mammalian Sec34 (a COG complex subunit) localizes to the Golgi apparatus, participates in ER-to-Golgi transport (anti-Sec34 antibodies inhibit VSVG transport in a semi-intact cell assay), and physically interacts with GTC-90 and ldlBp/ldlCp as part of the same multisubunit complex; direct interactions of Sec34 with ldlBp and ldlCp were demonstrated in vitro. Immunofluorescence, semi-intact cell transport assay with neutralizing antibodies, large-scale immunoprecipitation from rat liver cytosol, in vitro binding assay The Journal of biological chemistry High 11929878
2005 COG5 (Cog5) forms a stable subcomplex with Cog6 and Cog7 (lobe B), distinct from the Cog1–4 (lobe A) subcomplex; Cog8 bridges both subcomplexes into the complete COG complex; Cog5 deficiency causes mild Golgi cisternae dilation and partial glycosylation defects but not the full spectrum seen with Cog1/Cog2 loss, indicating subunit-specific roles. Only one or two of the Cog1/Cog2-dependent GEAR proteins are also sensitive to Cog5 deficiency. RNA interference knockdown of Cog5 in HeLa cells, immunoblotting, gel filtration, immunofluorescence microscopy, comparison with Cog1/Cog2 null CHO cells and Cog7-deficient fibroblasts The Journal of biological chemistry High 16051600
2009 Loss of COG5 protein (due to a splicing mutation causing exon skipping) delays retrograde Golgi-to-ER trafficking as measured by brefeldin-A treatment of patient fibroblasts, and causes defective N- and O-glycan sialylation; re-expression of wild-type COG5 cDNA restores normal trafficking kinetics. Brefeldin-A retrograde trafficking assay in patient fibroblasts, serum glycoprotein analysis, rescue by wild-type COG5 cDNA transfection Human molecular genetics High 19690088
2014 Crystal structure of the Cog5–Cog7 complex reveals that Cog5 adopts a CATCHR (complexes associated with tethering containing helical rods) fold, homologous to subunits of the Dsl1, exocyst, and GARP complexes. The Cog5–Cog7 interface is conserved from yeast to humans, and disruption of this interface in human cells causes defects in Golgi trafficking and glycosylation. X-ray crystallography of Cog5–Cog7 complex, biochemical interaction assays, functional studies in human cells with interface-disrupting mutations Proceedings of the National Academy of Sciences of the United States of America High 25331899
2020 COG5 variants cause fragmentation of the Golgi apparatus and upregulation of the UPR modulator PERK (PKR-like ER kinase), which in turn induces DNA damage in cultured cells and in murine retina, identifying a role for COG5 in maintaining ER protein homeostasis. Patient-derived cells with COG5 variants, immunofluorescence for Golgi morphology, western blotting for PERK and DNA damage markers, murine retinal analysis Scientific reports Medium 33277529
2024 A missense variant (p.Leu100Phe) in COG5 disrupts protein solubility and stability and abrogates the COG5–COG7 protein–protein interaction, as confirmed by co-immunoprecipitation in patient-derived cells. Co-immunoprecipitation in patient-derived cells, in silico structural analysis of COG5 variant effects on stability and solubility Journal of human genetics Medium 38987656
2026 COG5 deficiency leads to elevated cellular copper levels, which disrupts mitochondrial iron-sulfur cluster function and causes complex I assembly defects, resulting in impaired mitochondrial OXPHOS; these defects can be rescued by restoring COG5 expression or by copper chelation. Proteomic analysis of COG5-deficient and rescue cell models, biochemical validation of OXPHOS complex content, copper level measurements, copper chelator rescue experiments, patient-derived cells with COG5 variants PLoS genetics High 41824529
2024 In yeast, all lobe B COG subunits (Cog5–Cog8) are required for resistance to killer toxin K28; COG complex lobe B is needed for proper trafficking of the endolysosomal defence factor Ktd1, and its mis-localization in cog mutants accounts for hypersensitivity to the toxin beyond effects on surface glycosylation. High-throughput K28 sensitivity assay, fluorescence microscopy of Ktd1 localization in cog mutant yeast 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 103 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 19 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