GOSR2

GOSR2 (GS27/Membrin/Bos1) is a Golgi Qb-SNARE membrane protein that drives vesicular membrane fusion in the early secretory pathway (PMID:2007627, PMID:28982678). Genetic and biochemical work first placed its yeast ortholog BOS1 in the ER-to-Golgi transport step, where it is an essential membrane protein whose loss causes accumulation of ER and transport vesicles and failure to deliver secretory cargo to the Golgi (PMID:2192256, PMID:2007627). The human protein executes this function by assembling into a SNARE complex with syntaxin-5, Bet1, and Sec22b to catalyze ER-to-Golgi membrane fusion (PMID:28982678). Beyond this step, GOSR2 together with GS28 is enriched in COPI Golgi vesicles, and re-addition of isolated GS27/GS28-bearing vesicles is sufficient to restore intra-Golgi transport, indicating a role in inter-cisternal transport (PMID:23387339). Correct cis-Golgi localization is required for activity (PMID:21549339). The pathogenic p.Gly144Trp mutation causes loss of cis-Golgi targeting and partially reduces SNARE-mediated fusion by compromising the hydrophobic core that triggers SNARE assembly, while other mutations disrupt GOSR2–syntaxin-5 hydrogen bonding (PMID:21549339, PMID:28982678); these partial fusion deficits impair dendritic growth and destabilize the presynaptic cytoskeleton, underlying GOSR2 progressive myoclonus epilepsy (PMID:28978487). GOSR2 mutations are also associated with α-dystroglycan hypoglycosylation in patient fibroblasts that lack detectable bulk transport defects, linking GOSR2 to congenital muscular dystrophy (PMID:29855340).

1. 1990 High

   Established that the GOSR2 ortholog BOS1 acts in the same ER-to-Golgi transport step as BET1 and SEC22, defining its functional pathway before any molecular activity was known.

   Evidence Yeast multicopy suppression and double-mutant lethality analysis across multiple secretory mutant alleles

   PMID:2192256

   Open questions at the time

   • Genetic epistasis does not establish direct physical interaction or molecular mechanism
   • Does not define the biochemical activity of the gene product
2. 1991 High

   Showed BOS1 encodes an essential ~27-kDa membrane protein required for ER-to-Golgi cargo transport, converting a genetic interactor into a defined membrane trafficking component.

   Evidence Yeast depletion of essential gene, secretory cargo (pro-alpha-factor, CPY) trafficking assay, differential centrifugation

   PMID:2007627

   Open questions at the time

   • Molecular fusion mechanism not yet defined
   • SNARE partners not biochemically identified
3. 1999 Medium

   Cloned the human ortholog GS27/GOSR2 and mapped it to 17q21, transferring the yeast trafficking role into a human SNARE candidate.

   Evidence cDNA cloning, sequence analysis, chromosomal mapping

   PMID:10198168

   Open questions at the time

   • Function inferred from homology, not directly tested in human cells
   • SNARE complex membership not experimentally shown here
4. 2011 Medium

   Demonstrated that the disease mutation p.Gly144Trp abolishes cis-Golgi localization, establishing correct localization as a functional requirement and the molecular basis of loss of function.

   Evidence Patient mutation identification and immunofluorescence localization in patient-derived cells

   PMID:21549339

   Open questions at the time

   • Mechanism of mislocalization at the protein level not resolved
   • Single-lab observation
   • Downstream trafficking consequences not quantified here
5. 2013 High

   Reconstituted a vesicle-level role for GS27/GS28, showing the two SNAREs are enriched in COPI vesicles and sufficient to restore intra-Golgi transport, extending GOSR2 function beyond the ER-to-Golgi step.

   Evidence Subcellular fractionation, in vitro intra-Golgi transport assay with selective vesicle re-addition under transport block

   PMID:23387339

   Open questions at the time

   • Does not resolve the specific SNARE pairing for intra-Golgi fusion
   • Relationship between COPI vesicle role and ER-Golgi role unclear
6. 2017 High

   Identified the human SNARE complex (GOSR2-syntaxin-5-Bet1-Sec22b) and showed disease mutations cause partial fusion deficits, providing the molecular mechanism linking genotype to impaired membrane fusion.

   Evidence Yeast complementation, fluorescence anisotropy, gel filtration, molecular dynamics simulation with mutagenesis

   PMID:28982678

   Open questions at the time

   • Quantitative link between residual fusion activity and tissue-specific disease severity not established
   • In vivo fusion kinetics not measured
7. 2017 High

   Connected partial SNARE fusion deficits to neuronal phenotypes, revealing roles for Membrin in dendritic growth and presynaptic cytoskeletal/transsynaptic integrity relevant to progressive myoclonus epilepsy.

   Evidence Drosophila loss-of-function models (dendritic morphology, electrophysiology, cytoskeletal imaging) plus SNARE fusion assay

   PMID:28978487

   Open questions at the time

   • Mechanistic link between trafficking deficit and cytoskeletal fragmentation not fully defined
   • Findings in Drosophila not validated in mammalian neurons here
8. 2018 Medium

   Linked GOSR2 mutations to α-dystroglycan hypoglycosylation and congenital muscular dystrophy while showing no detectable bulk transport defect, indicating a selective rather than global trafficking consequence.

   Evidence Patient fibroblast analysis, western blotting/immunofluorescence for α-dystroglycan glycosylation, live-cell transport assays with model cargoes

   PMID:29855340

   Open questions at the time

   • Mechanism connecting GOSR2 dysfunction to selective glycosylation defect unresolved
   • Single patient, single lab
   • Negative transport result may reflect assay sensitivity

• How partial GOSR2 fusion deficits produce tissue-selective outcomes (neuronal epilepsy versus muscle glycosylation defects) without overt bulk secretory failure remains unresolved.
• No mechanism explaining selective vulnerability of specific cargoes or tissues
• Direct structural model of the assembled human SNARE complex absent
• Link between intra-Golgi role and glycosylation phenotype not established