Kpc1 (CG6752) is the Drosophila homologue of KPC1/RNF123, a large SPRY- and RING-finger-containing E3 ubiquitin ligase. With its partner Kpc2 (the UBAC1/KPC2 homologue) it forms the KIP1 ubiquitination-promoting complex (KPC); the two proteins co-immunoprecipitate from testes and stabilize one another, and Kpc1 is required for monoubiquitination of Kpc2. Kpc1 is enriched in the male germ line and localizes, with Kpc2, to the tip of the mature sperm flagellum, where the complex is required for localization of the polycystin-2 channel Amo; loss of Kpc1 causes failure of sperm storage in females and male sterility. Direct fly substrates of its ligase activity have not been identified.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000151 ubiquitin ligase complex | IPI PMID:33378371 A genetic screen in Drosophila reveals an unexpected role fo... | ACCEPT | Summary: Kpc1 forms the KPC ubiquitin ligase complex with Kpc2. Reason: Reciprocal co-IP from testes and mutual stabilization establish the fly KPC complex. Supporting Evidence: PMID:33378371 Similar to the vertebrate KPC complex, co-IP experiments showed that dKPC1 and dKPC2 physically interact and stabilize one another in a reciprocal fashion. |
| GO:0000151 ubiquitin ligase complex | IPI PMID:33378371 A genetic screen in Drosophila reveals an unexpected role fo... | ACCEPT | Summary: Kpc1 forms the KPC ubiquitin ligase complex with Kpc2. Reason: Reciprocal co-IP from testes and mutual stabilization establish the fly KPC complex. Supporting Evidence: PMID:33378371 Similar to the vertebrate KPC complex, co-IP experiments showed that dKPC1 and dKPC2 physically interact and stabilize one another in a reciprocal fashion. |
| GO:0004842 ubiquitin-protein transferase activity | IBA GO_REF:0000033 | MODIFY | Summary: Kpc1 is a RING-type E3 ubiquitin transferase. Reason: Correct (conserved RING E3 of the RNF123 family; phylogenetic and domain inference, supported in fly by Kpc1-dependent monoubiquitination of Kpc2), but a less informative parent; MODIFY to ubiquitin protein ligase activity, which Kpc1 already carries (IEA, ISS). Proposed replacements: ubiquitin protein ligase activity Supporting Evidence: PMID:33378371 KPC is a heterodimer composed of KPC1, an E3 ligase, and KPC2 (or UBAC1), an adaptor protein |
| GO:0004842 ubiquitin-protein transferase activity | IEA GO_REF:0000002 | MODIFY | Summary: Kpc1 is a RING-type E3 ubiquitin transferase. Reason: Correct (conserved RING E3 of the RNF123 family; phylogenetic and domain inference, supported in fly by Kpc1-dependent monoubiquitination of Kpc2), but a less informative parent; MODIFY to ubiquitin protein ligase activity, which Kpc1 already carries (IEA, ISS). Proposed replacements: ubiquitin protein ligase activity Supporting Evidence: PMID:33378371 KPC is a heterodimer composed of KPC1, an E3 ligase, and KPC2 (or UBAC1), an adaptor protein |
| GO:0005515 protein binding | IPI PMID:33378371 A genetic screen in Drosophila reveals an unexpected role fo... | REMOVE | Summary: Kpc1 co-immunoprecipitates with Kpc2. Reason: Bare protein binding is uninformative; the interaction is captured by ubiquitin ligase complex membership. Removal does not imply the interaction is false. Supporting Evidence: PMID:33378371 Like their mammalian counterparts Drosophila KPC1 and KPC2 physically interact and they stabilize one another at the protein level |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: KPC acts in the cytoplasm. Reason: Phylogenetically inferred cytoplasmic activity, consistent with a soluble E3 complex; correct but general, since the functional location in fly is the sperm flagellum tip. |
| GO:0008150 biological_process | ND GO_REF:0000015 | REMOVE | Summary: No-data biological process placeholder. Reason: Superseded by the existing NAS sperm storage annotation and IEA protein ubiquitination; an ND placeholder is no longer appropriate. |
| GO:0008270 zinc ion binding | ISM PMID:21912646 Comprehensively surveying structure and function of RING dom... | KEEP AS NON CORE | Summary: RING finger zinc coordination. Reason: Structural property of the RING domain inferred from sequence; correct but not a functional activity. Supporting Evidence: PMID:21912646 besides the conserved Cys/His chelating zinc ions |
| GO:0016567 protein ubiquitination | IEA GO_REF:0000117 | ACCEPT | Summary: Kpc1 mediates protein ubiquitination. Reason: Consistent with RING E3 activity and with loss of Kpc2 monoubiquitination in Kpc1 mutants. Supporting Evidence: PMID:33378371 In flies, KPC2 is monoubiquitinated and phosphorylated and this modified form of the protein is located in mature sperm |
| GO:0030163 protein catabolic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic transfer of KPC-mediated protein degradation. Reason: Mammalian KPC ubiquitinates p27 for degradation; in fly no degradation substrate is known and the established effect is stabilization of Kpc2, so this inherited role is plausible but not central to known fly biology. Supporting Evidence: file:DROME/Kpc1/Kpc1-deep-research-falcon.md Amo is a downstream localization client, not a demonstrated ubiquitination substrate. |
| GO:0030163 protein catabolic process | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: Phylogenetic transfer of KPC-mediated protein degradation. Reason: Mammalian KPC ubiquitinates p27 for degradation; in fly no degradation substrate is known and the established effect is stabilization of Kpc2, so this inherited role is plausible but not central to known fly biology. Supporting Evidence: file:DROME/Kpc1/Kpc1-deep-research-falcon.md Amo is a downstream localization client, not a demonstrated ubiquitination substrate. |
| GO:0036126 sperm flagellum | IDA PMID:33378371 A genetic screen in Drosophila reveals an unexpected role fo... | ACCEPT | Summary: Kpc1 localizes to the tip of the sperm flagellum. Reason: Directly observed by immunostaining of mature sperm. Supporting Evidence: PMID:33378371 Neither KPC1 nor KPC2 directly interact with Amo but they are detected in proximity to Amo at the tip of the sperm flagellum |
| GO:0046693 sperm storage | NAS PMID:33378371 A genetic screen in Drosophila reveals an unexpected role fo... | KEEP AS NON CORE | Summary: Kpc1 mutant males fail to store sperm in females. Reason: A genetic requirement mediated through Amo localization at the sperm tail tip; Kpc1 does not itself perform sperm storage, so this is a downstream physiological role. Supporting Evidence: PMID:33378371 Male flies lacking either KPC1 or KPC2 phenocopy amo mutants and are sterile due to a failure of sperm storage |
| GO:0061630 ubiquitin protein ligase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Kpc1 is a RING E3 ubiquitin ligase. Reason: Conserved RNF123-family RING E3; fly Kpc1 is required for Kpc2 monoubiquitination. Supporting Evidence: PMID:33378371 KPC is a heterodimer composed of KPC1, an E3 ligase, and KPC2 (or UBAC1), an adaptor protein |
| GO:0061630 ubiquitin protein ligase activity | ISS GO_REF:0000024 | ACCEPT | Summary: Kpc1 is a RING E3 ubiquitin ligase. Reason: Conserved RNF123-family RING E3; fly Kpc1 is required for Kpc2 monoubiquitination. Supporting Evidence: PMID:33378371 KPC is a heterodimer composed of KPC1, an E3 ligase, and KPC2 (or UBAC1), an adaptor protein |
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Download this section (compressed HTML)Q: What are the direct ubiquitination substrates of fly KPC at the sperm flagellar tip, and how does KPC activity promote Amo localization without binding Amo?
Experiment: Rescue Kpc1 mutants with a RING-dead Kpc1 transgene and test Kpc2 monoubiquitination, Amo tip localization and sperm storage; combine with proximity labeling at the flagellar tip to identify candidate substrates.
Hypothesis: Kpc1 RING catalytic activity, not only complex scaffolding, is required for Amo localization and sperm storage.
Type: structure-function rescue
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