CLN8 is an endoplasmic-reticulum membrane protein with distinct cargo-receptor and lipid-acyltransferase activities. Together with CLN6 it recruits newly synthesized lysosomal enzymes, engages COPII coat machinery and escorts selected enzymes toward the Golgi before returning to the ER through a C-terminal retrieval signal. CLN8 also transfers acyl groups from acyl-CoA to lysophosphatidylglycerol to form bis(monoacylglycero)phosphate, contributing to cellular BMP pools. Loss of CLN8 disrupts lysosomal enzyme delivery and lipid balance and causes neuronal ceroid lipofuscinosis with progressive neurological decline.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:17237713 Neuronal ceroid lipofuscinosis: a common pathway? | KEEP AS NON CORE | Summary: Retain the experimentally observed association with CLN3. Reason: The original full paper detects CLN3 after CLN8 immunoprecipitation from normal lymphoblast lysate and reports reciprocal experiments with transfected COS-7 cells. The Methods include presera and unrelated-protein controls. This supports the positive association without establishing an autonomous adapter activity or requiring every interaction to occur at the steady-state ER location. The project-specific curation instruction retains a supported association as non-core when no evidence-backed refinement is established; it does not infer an adaptor function from binding alone. |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: Retain the curated ER localization. Reason: The PAINT assignment is corroborated by direct human CLN8 localization and later cargo-receptor experiments. Current donor records include human CLN8 and TLCD3B ER experiments; target self-inclusion is legitimate experimental grounding. Historical ancestral placement was not independently reconstructed, so the source assessment records that limit separately from the positive target judgment. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000335242 UNRESOLVED Current experimental ER premises and target localization support retention, but the historical node placement was not reconstructed. Supporting Evidence: GO_REF:0000033 file:human/CLN8/CLN8-source-evidence.json |
| GO:0005783 endoplasmic reticulum | IDA PMID:10861296 The neuronal ceroid lipofuscinosis CLN8 membrane protein is ... | ACCEPT | Summary: Retain the original human CLN8 ER localization. Reason: The authentic abstract reports human CLN8 expressed in BHK, HeLa and CHO cells, with predominant ER localization and partial ERGIC localization. The author thesis describes the original marker and retrieval-motif experiments, while later full papers independently establish the ER compartment. Original journal full-text access remains unavailable; the thesis is not represented as the original article. |
| GO:0005783 endoplasmic reticulum | IDA PMID:19941651 Novel interactions of CLN5 support molecular networking betw... | ACCEPT | Summary: Retain ER localization in the CLN5 trafficking study. Reason: The full study shows overexpressed CLN8 remaining in the ER in HeLa cells, including coexpression with trafficking-deficient human CLN5. The CLN5 fusion-protein pull-downs and mouse comparisons are separate experiments; the location annotation does not depend on assigning their species to the human imaging. Supporting Evidence: |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000120 | ACCEPT | Summary: Retain the combined ER localization inference. Reason: The authenticated mouse Cln8 ortholog and subcellular-vocabulary source are consistent with the direct human ER localization. The original combined source fields are preserved, and the mouse donor has experimental ER evidence rather than merely a matching gene name. Propagation Review Root cause: NO FAILURE CORE Sources checked: UniProtKB:Q9QUK3 SUPPORTS TRANSFER Official identity and current mouse experimental ER annotation corroborate the conserved location, independently supported in human CLN8. Supporting Evidence: GO_REF:0000120 file:human/CLN8/CLN8-source-evidence.json |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Retain the ER membrane as the main working compartment. Reason: CLN8 is an integral membrane cargo receptor whose cytosolic motifs recruit coat machinery while a luminal region recruits lysosomal enzymes. This experimentally supported topology and ER localization substantiate the subcellular-vocabulary mapping. |
| GO:0005793 endoplasmic reticulum-Golgi intermediate compartment | IDA PMID:10861296 The neuronal ceroid lipofuscinosis CLN8 membrane protein is ... | ACCEPT | Summary: Retain CLN8 cycling through the ERGIC. Reason: The original authentic abstract reports partial ERGIC localization and redistribution after retrieval-motif mutation. The original author thesis supplies marker and recycling context; later cargo-receptor experiments support an ER-to-Golgi itinerary. ER residence does not exclude this cycling compartment. |
| GO:0006644 phospholipid metabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: Retain inherited phospholipid metabolism with direct target corroboration. Reason: The original human and mouse premises concern lipid-profile phenotypes, while later purified human CLN8 directly transfers acyl groups from acyl-CoA to LPG to form BMP. That chemistry independently supports phospholipid metabolism. It does not reconstruct the PAINT node or imply that each lipid change in deficient brain is a direct CLN8 reaction. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002668182 UNRESOLVED Current experimental lipid premises and direct target catalysis support the target function; historical ancestral placement remains uninspected. Supporting Evidence: GO_REF:0000033 file:human/CLN8/CLN8-source-evidence.json |
| GO:0006644 phospholipid metabolic process | IMP PMID:16086686 Mass spectrometric analysis reveals changes in phospholipid,... | ACCEPT | Summary: Retain the original phospholipid phenotype with later catalytic support. Reason: The original authentic abstract describes altered phospholipid species in two human EPMR brain samples at different disease stages. Its full Methods were not recovered, and those profiles alone do not identify a reaction. Independent purified human CLN8 and knockout/rescue experiments now establish phospholipid synthesis and cellular BMP control, supporting retention of this broad process. |
| GO:0006672 ceramide metabolic process | IMP PMID:16086686 Mass spectrometric analysis reveals changes in phospholipid,... | UNDECIDED | Summary: Preserve the positive ceramide phenotype while leaving process scope unresolved. Reason: The original abstract explicitly reports reduced ceramide and related sphingolipids in a patient brain sample. The full experimental and interpretive context could not be recovered, and the later demonstrated LPG acylation does not itself establish a ceramide-metabolic step. The source-specific assertion remains unresolved without denying the lipid change or claiming the curator tested the wrong gene. |
| GO:0006869 lipid transport | NAS PMID:12151215 TRAM, LAG1 and CLN8: members of a novel family of lipid-sens... | UNDECIDED | Summary: The original lipid-transport proposal remains unverified. Reason: The accessible source abstract proposes lipid-related functions from TLC-family relationships, but the full analysis was not recovered. CLN8 protein-cargo export and phospholipid acylation are directly supported activities; neither demonstrates movement of a lipid cargo. Preserve the NAS source as unresolved rather than converting protein transport into lipid transport. |
| GO:0007399 nervous system development | IBA GO_REF:0000033 | UNDECIDED | Summary: The inherited developmental-process scope remains unresolved. Reason: The current human premise is the original disease-gene report, and the mouse record contains inherited developmental assertions. The actual human paper establishes mutations and progressive degeneration, which do not identify a developmental operation performed by CLN8. This limits target process interpretation but does not demonstrate a misplaced ancestral node, lineage-specific loss or circular propagation. See the separate PMID:10508524 assertion for the inspected disease-gene evidence; its over-annotation judgment does not settle the uninspected historical PAINT placement. Propagation Review Root cause: UNRESOLVED Sources checked: PANTHER:PTN002668182 UNRESOLVED The historical developmental node was not reconstructed; the inspected target disease evidence does not resolve a performed developmental step. |
| GO:0007399 nervous system development | IMP PMID:10508524 The neuronal ceroid lipofuscinoses in human EPMR and mnd mut... | MARK AS OVER ANNOTATED | Summary: The disease-gene experiment does not establish a developmental operation. Reason: The original full article identifies pathogenic human CLN8 variants and the mouse mnd mutation and describes progressive neurological deterioration. Human fetal-brain material is used in cloning and expression work; it is not an assay demonstrating that CLN8 executes nervous-system development. The source-specific process assignment exceeds the demonstrated role, without denying the neuronal phenotype or excluding a separate developmental function. The separate IBA row remains UNDECIDED because its ancestral placement has not been reconstructed; that is a distinct provenance question, not a reversal of this source-specific assessment. |
| GO:0008203 cholesterol metabolic process | IMP PMID:16086686 Mass spectrometric analysis reveals changes in phospholipid,... | UNDECIDED | Summary: The cholesterol-specific source support remains inaccessible. Reason: The original complete abstract reports phospholipid and sphingolipid profiles, but it does not expose the cholesterol experiment or reasoning behind this IMP assertion. Full-text recovery failed. Neither that access gap nor the later BMP reaction is evidence that cholesterol effects are absent, so the original annotation is left unresolved. Supporting Evidence: |
| GO:0008610 lipid biosynthetic process | NAS PMID:12151215 TRAM, LAG1 and CLN8: members of a novel family of lipid-sens... | ACCEPT | Summary: Retain lipid synthesis in light of direct CLN8 catalysis. Reason: The original TLC-family paper offers a broad lipid-function hypothesis at the accessible abstract level. Later purified human CLN8 forms BMP by acyl-CoA-dependent acylation of an LPG substrate, providing independent positive evidence for lipid biosynthesis. This does not validate the older proposal of ceramide synthesis or establish the complete stereochemical route to mature S,S-BMP. |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: Specify the experimentally established ER membrane. Reason: The TLC-domain membrane inference is compatible with CLN8, and later human localization, topology and COPII-recruitment assays resolve the ER membrane as a more informative compartment. The protein also cycles through the early secretory pathway, so this refinement does not assert exclusive residence. Proposed replacements: endoplasmic reticulum membrane |
| GO:0016020 membrane | NAS PMID:10508524 The neuronal ceroid lipofuscinoses in human EPMR and mnd mut... | MODIFY | Summary: Specify the experimentally established ER membrane. Reason: The original sequence-based membrane prediction is compatible with CLN8, and later human localization, topology and COPII-recruitment assays resolve the ER membrane as a more informative compartment. The protein also cycles through the early secretory pathway, so this refinement does not assert exclusive residence. Proposed replacements: endoplasmic reticulum membrane |
| GO:0016020 membrane | NAS PMID:10861296 The neuronal ceroid lipofuscinosis CLN8 membrane protein is ... | MODIFY | Summary: Specify the experimentally established ER membrane. Reason: The original experimentally observed membrane association is compatible with CLN8, and later human localization, topology and COPII-recruitment assays resolve the ER membrane as a more informative compartment. The protein also cycles through the early secretory pathway, so this refinement does not assert exclusive residence. Proposed replacements: endoplasmic reticulum membrane |
| GO:0030163 protein catabolic process | NAS PMID:10740217 Batten's disease: clues to neuronal protein catabolism in ly... | MARK AS OVER ANNOTATED | Summary: Historical NCL catabolism speculation does not establish CLN8 proteolysis. Reason: The authentic review abstract uses the historical label CLN8 for cathepsin D and proposes a common lysosomal protein-catabolism function. This is not a demonstrated protein-breakdown activity of the modern CLN8 gene product. Later work identifies CLN8 as a cargo receptor and lipid acyltransferase; lysosomal enzymes perform the degradation. The original citation is preserved with this explicit nomenclature and participant-scope limitation. |
| GO:0033116 endoplasmic reticulum-Golgi intermediate compartment membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Retain the membrane compartment of CLN8 early-secretory cycling. Reason: CLN8 is membrane embedded and moves through the ERGIC during its ER-to-Golgi itinerary. The subcellular-vocabulary mapping is consistent with the original human location report and subsequent motif-dependent transport experiments. |
| GO:0045861 negative regulation of proteolysis | NAS PMID:12151215 TRAM, LAG1 and CLN8: members of a novel family of lipid-sens... | UNDECIDED | Summary: The original negative-proteolysis proposal is not resolved. Reason: The original full family-analysis paper was inaccessible, so the basis for this NAS regulatory assertion could not be inspected. Later CLN8 deficiency increases degradation of retained lysosomal enzymes, but that cargo-protection context should not silently stand in for the original broad negative-regulation claim. No direct protease-inhibitor activity is inferred. |
| GO:0046513 ceramide biosynthetic process | NAS PMID:12151215 TRAM, LAG1 and CLN8: members of a novel family of lipid-sens... | UNDECIDED | Summary: The historical ceramide-synthesis proposal remains unresolved. Reason: The accessible source proposes lipid-related functions from a shared TLC domain. Direct modern CLN8 catalysis instead uses LPG and acyl-CoA to make BMP; this does not establish ceramide synthesis, but it also does not exclude an untested contribution to ceramide metabolism. The inaccessible original full analysis prevents a source-specific resolved judgment. |
| GO:0055088 lipid homeostasis | IBA GO_REF:0000033 | ACCEPT | Summary: Retain lipid homeostasis with direct human target support. Reason: The curated family transfer has experimental lipid-homeostasis premises in TLCD proteins, with the exact current donor records retained separately. Human CLN8 loss strongly decreases cellular BMP, and CLN8 re-expression restores it alongside direct purified-enzyme activity. These target data substantiate the homeostatic role without claiming to reconstruct the historical PAINT placement or transferring TLCD1 substrate specificity to CLN8. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN001412312 UNRESOLVED Current experimental family premises and direct target BMP control support retention; historical node placement and the unresolved WormBase identifier mapping are recorded separately. |
| GO:0097001 ceramide binding | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Retain curated ceramide binding at the measured overlay scope. Reason: The target itself is an experimentally grounded source: the original paper detects CLN8 on ceramide and galactosylceramide spots after incubation with normal-cell lysate. This is positive ligand-association evidence, but it is not purified binary affinity or a ceramide-transport assay. Retain the non-core activity while keeping historical PAINT placement distinct from the target experiment. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN002668182 UNRESOLVED The exact target ligand-overlay premise is positive; ancestral placement was not independently reconstructed. |
| GO:0097001 ceramide binding | IDA PMID:18317235 CLN3p impacts galactosylceramide transport, raft morphology,... | KEEP AS NON CORE | Summary: Retain the original CLN8-positive ceramide overlay. Reason: The full paper explicitly reports CLN8 signal on ceramide and galactosylceramide spots in the normal-cell lysate overlay and presents the CLN8 result in Figure 7D. The CLN3-centered title does not erase this target experiment. The mixed-cell study does not provide a purified CLN8 affinity measurement or demonstrate that CLN8 transports ceramide. |
| GO:0097020 COPII receptor activity | IDA PMID:30397314 CLN8 is an endoplasmic reticulum cargo receptor that regulat... | NEW | Summary: Add the directly demonstrated COPII cargo-receptor activity. Reason: Human CLN8 recruits newly synthesized lysosomal enzymes through its luminal region and engages Sec24A/C through a cytosolic export motif. Mutation and knockout/rescue experiments separate cargo recruitment, coat interaction and ER exit; later COPII budding confirms CLN8 inclusion while CLN6 remains in the ER. This performed receptor activity is not covered by the original generic binding annotation. Supporting Evidence: PMID:30397314 interaction of CLN8 with Sec24a and Sec24c |
| GO:0071617 lysophospholipid acyltransferase activity | IDA PMID:39970228 TRAM-LAG1-CLN8 family proteins are acyltransferases regulati... | NEW | Summary: Add the directly measured lysophospholipid acyltransferase activity. Reason: Purified HA-tagged human CLN8 transfers an acyl group from acyl-CoA onto the headgroup of the tested racemic-headgroup LPG substrate, producing BMP detected by radiolabel/TLC and diagnostic LC-MS/MS. Enzyme/substrate controls and separate purification batches support the activity. The synthesized coding sequence matches canonical Q9UBY8 exactly; no alternative product is seeded. Product stereochemistry is not fully resolved, and TLCD1 kinetic constants or catalytic-mutant controls are not transferred to CLN8. GO:0160121 instead specifies transfer between two LPG molecules, producing BMP and glycerophosphoglycerol; it does not describe the measured acyl-CoA donor reaction. Supporting Evidence: PMID:39970228 purified CLN8 preferentially synthesized BMP in a time-dependent manner file:human/CLN8/CLN8-source-evidence.json |
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Download this section (compressed HTML)Q: How are CLN8 cargo recruitment and lipid acylation coupled in the ER, and can either activity be selectively disrupted without altering folding or retrieval?
Q: Which stereochemically defined BMP products does endogenous CLN8 make, and which enzymes perform any subsequent glycerol inversion steps?
Q: What full-text evidence underlies the older CLN8 lipid-transport, ceramide-synthesis, cholesterol-metabolism and negative-proteolysis assertions?
Q: Which experiments distinguish a direct CLN8 role in nervous-system development from later neuronal maintenance and degeneration?
Q: Does purified CLN8 reproduce the historical ceramide/GalCer overlay signal, and what are its affinity and lipid specificity in a membrane environment?
Experiment: Compare sequence-defined human CLN8 with folding- and localization-controlled mutants in both lysosomal-enzyme recruitment/COPII export assays and purified LPG-acylation assays.
Experiment: Use enantiomerically defined LPG substrates and chiral product analysis to distinguish the immediate CLN8 product from downstream S,S-BMP, with enzyme-free and substrate-free controls.
Experiment: Measure cargo delivery, BMP pools and neuronal survival after endogenous rescue with variants that selectively preserve one of the two CLN8 activities.
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