PEF-1 (Phosphatase with EF-hands 1) is the sole C. elegans member of the RdgC/PPEF family of serine/threonine protein phosphatases, distinguished by C-terminal EF-hand calcium-binding domains. Expression is restricted to sensory neurons including ciliated chemosensory neurons AWB, AWC, ASE, AFD, BAG, and others. The protein localizes to sensory cilia via N-terminal myristoylation (Gly-2) and palmitoylation (Cys-3), where it is enriched in the ciliary axoneme and excluded from the transition zone. PEF-1 requires transition zone proteins (MKS-5, CEP-290) for proper ciliary compartmentalization. Functional studies demonstrate that pef-1 mutants show defects in thermotaxis, salt chemotaxis, CO2 avoidance, and UV light avoidance, while osmosensation remains normal. TEM analysis reveals microtubule abnormalities in pef-1 mutant cilia, suggesting a role in cilium maintenance. The protein binds calcium via its EF-hands and binds manganese as a cofactor for phosphatase activity. This is the first PPEF family member demonstrated to function in cilia; in contrast, the Drosophila ortholog RdgC functions in non-ciliary rhabdomeric photoreceptors.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005634 nucleus | IBA GO_REF:0000033 | REMOVE | Summary: IBA annotation based on phylogenetic inference from other PPEF family members. However, the 2001 study by Ramulu and Nathans (PMID:11312268) found CePPEF to be membrane-associated via lipid modifications and localized to neuronal cell bodies, dendrites, axons, and cilia. No nuclear localization was observed in C. elegans. The 2024 study (PMID:39550471) confirms ciliary localization. Nuclear localization may be an artifact of heterologous expression systems or represent a minor non-conserved localization in other species. Reason: No experimental evidence supports nuclear localization of PEF-1 in C. elegans. Both PMID:11312268 and PMID:39550471 show exclusive membrane/ciliary localization in sensory neurons. The phylogenetic inference may not apply to this species. Supporting Evidence: PMID:11312268 In transgenic C. elegans and in transfected 293 cells, CePPEF is membrane-associated, and the N terminus of CePPEF is necessary and sufficient for this membrane association. PMID:39550471 we found the PEF-1::GFP protein to be concentrated within the cilium, but in a region distal to the transition zone (TZ), which represents the proximal-most region of the axoneme file:worm/pef-1/pef-1-deep-research-falcon.md model: Edison Scientific Literature |
| GO:0005829 cytosol | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA annotation based on phylogenetic inference. While some cytosolic localization may occur, the predominant localization in C. elegans is membrane-associated and ciliary. The protein requires myristoylation and palmitoylation for proper localization. Cytosolic localization is likely minimal and not the primary site of function. Reason: While membrane association is the predominant localization, some cytosolic presence may occur during protein synthesis/transport. However, the core function is at cilia and cell membrane. The IBA inference from other species may reflect different localization patterns in those organisms. Supporting Evidence: PMID:11312268 In transgenic C. elegans and in transfected 293 cells, CePPEF is membrane-associated |
| GO:0004722 protein serine/threonine phosphatase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Core molecular function of PEF-1 supported by sequence homology to the RdgC/PPEF family, presence of PPP phosphatase domain, and catalytic residues. The protein contains a well-characterized metallophos domain with manganese-binding sites essential for catalysis. UniProt annotates EC 3.1.3.16 activity. Reason: Protein serine/threonine phosphatase activity is the defining molecular function of the PPEF family. PEF-1 contains all necessary catalytic domains and cofactor binding sites. This is strongly supported by phylogenetic analysis and domain architecture. Supporting Evidence: PMID:11312268 The RdgC/PPEF family of serine/threonine protein phosphatases is distinguished by the presence of C-terminal EF-hands and neuron-specific expression, including frequent expression in primary sensory neurons |
| GO:0004721 phosphoprotein phosphatase activity | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation from InterPro domain IPR012008. This is a parent term of GO:0004722 (protein serine/threonine phosphatase activity). The more specific child term is already annotated with IBA evidence. Reason: This broader term is consistent with the protein's function and is appropriately inferred from domain architecture. The IEA annotation is valid alongside the more specific IBA annotation for GO:0004722. |
| GO:0004722 protein serine/threonine phosphatase activity | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation based on Rhea reaction mapping and EC number. This duplicates the IBA annotation but with different evidence source. Both are valid. Reason: This annotation from reaction/EC mapping provides independent support for the core phosphatase function. Duplicate GO IDs with different evidence codes are acceptable. |
| GO:0005506 iron ion binding | IEA GO_REF:0000002 | REMOVE | Summary: IEA annotation from InterPro domain IPR012008. However, PPP phosphatases typically use manganese, not iron, as the catalytic metal. UniProt specifically annotates manganese binding for this protein based on similarity to P36873. Iron binding is not established for PPEF family members. Reason: This is likely an incorrect inference. PPEF family phosphatases use manganese as the catalytic metal ion. UniProt annotation and experimental evidence from related proteins indicate manganese binding, not iron. The InterPro inference may be overly broad. |
| GO:0005509 calcium ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: Core function supported by experimental evidence. PEF-1 contains three EF-hand domains that bind calcium. Ramulu and Nathans (2001) demonstrated calcium binding experimentally using recombinant protein. Reason: Calcium binding is a defining feature of the PPEF family and has been experimentally verified for CePPEF. The EF-hand domains (residues 546-581, 629-664, 669-704) bind 1-2 calcium ions per protein. Supporting Evidence: PMID:11312268 A recombinant C-terminal fragment of CePPEF containing two putative EF-hands bound between one and two Ca(2+) ions/protein, and mutation of residues presumed to ligand calcium in the two putative EF-hands led to diminished calcium binding |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Supported by experimental evidence. PEF-1 is membrane-associated through N-terminal myristoylation and palmitoylation. UniProt annotation is based on PMID:11312268. Reason: Membrane association via lipid anchors is experimentally established and essential for proper localization and function. Supporting Evidence: PMID:11312268 [(3)H]Myristate and [(3)H]palmitate labeling studies in 293 cells demonstrated that this association was mediated by myristoylation at Gly(2) and palmitoylation at Cys(3) |
| GO:0005929 cilium | IEA GO_REF:0000044 | ACCEPT | Summary: Core localization strongly supported by experimental evidence from both 2001 and 2024 studies. PEF-1 is highly enriched in sensory cilia of chemosensory neurons. The 2024 study provides detailed characterization of ciliary localization and transition zone dependency. Reason: Ciliary localization is a defining characteristic of PEF-1 function in C. elegans. The protein localizes to the axonemal region, requires transition zone proteins for compartmentalization, and functions in cilium-dependent sensory behaviors. Supporting Evidence: PMID:11312268 Neurons expressing CePPEF include the ciliary chemosensory neurons AWB and AWC; and within these neurons, CePPEF is highly enriched in the sensory cilia PMID:39550471 we found the PEF-1::GFP protein to be concentrated within the cilium, but in a region distal to the transition zone (TZ), which represents the proximal-most region of the axoneme |
| GO:0016787 hydrolase activity | IEA GO_REF:0000120 | MARK AS OVER ANNOTATED | Summary: Very general term that is a parent of phosphatase activity. While technically correct, the more specific phosphatase terms are more informative. Reason: This is too general to be informative. The more specific GO:0004722 (protein serine/threonine phosphatase activity) already captures the molecular function. Hydrolase activity adds no additional information. |
| GO:0030145 manganese ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: Core cofactor binding function. PPP phosphatases require manganese for catalysis. UniProt annotates binding of 2 manganese ions per subunit based on similarity to experimentally characterized family members. Reason: Manganese binding is essential for phosphatase catalytic activity and is well-supported by domain architecture and similarity to characterized PPP phosphatases. The metallophos domain contains conserved manganese-binding residues. |
| GO:0030424 axon | IEA GO_REF:0000044 | ACCEPT | Summary: Supported by experimental evidence. Ramulu and Nathans (2001) showed CePPEF localization in axons of sensory neurons. The G2A mutation disrupted axonal localization. Reason: Axonal localization is experimentally demonstrated as part of the neuronal distribution pattern. Supporting Evidence: PMID:11312268 Introducing the G2A or C3S mutation into CePPEF greatly reduced membrane association in 293 cells and in transgenic nematodes |
| GO:0030425 dendrite | IEA GO_REF:0000044 | ACCEPT | Summary: Supported by experimental evidence. Ramulu and Nathans (2001) showed CePPEF localization in dendrites of sensory neurons. Reason: Dendritic localization is experimentally demonstrated as part of the neuronal distribution pattern. Supporting Evidence: PMID:11312268 Introducing the G2A or C3S mutation into CePPEF greatly reduced membrane association in 293 cells and in transgenic nematodes |
| GO:0043204 perikaryon | IEA GO_REF:0000044 | ACCEPT | Summary: Supported by experimental evidence. UniProt annotation derived from PMID:11312268 which demonstrated expression in neuronal cell bodies. Reason: Perikaryon (neuronal cell body) localization is experimentally demonstrated. Supporting Evidence: PMID:11312268 Neurons expressing CePPEF include the ciliary chemosensory neurons AWB and AWC |
| GO:0046872 metal ion binding | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: Very general term encompassing the more specific manganese and calcium binding functions. While technically correct, the specific metal ion binding terms are more informative. Reason: This is too general to be informative. The more specific GO:0030145 (manganese ion binding) and GO:0005509 (calcium ion binding) already capture the specific metal binding functions. |
| GO:0050906 detection of stimulus involved in sensory perception | IEA GO_REF:0000002 | MODIFY | Summary: Supported by the 2024 functional studies (PMID:39550471) which demonstrate PEF-1 is required for multiple sensory modalities including thermosensation, chemosensation (salt), CO2 sensing, and UV light detection. However, the term may be too broad - the protein is not directly detecting stimuli but rather modulating ciliary signaling pathways. Reason: While PEF-1 is involved in sensory processes, it is not a receptor that directly detects stimuli. Rather, it modulates sensory signaling in cilia. More specific behavioral or regulatory terms would be more accurate. Proposed replacements: thermosensory behavior detection of stimulus involved in sensory perception Supporting Evidence: PMID:39550471 pef-1 mutants have a lower attraction to salt compared to wild-type animals |
| GO:0043025 neuronal cell body | IDA PMID:11312268 Cellular and subcellular localization, N-terminal acylation,... | ACCEPT | Summary: Direct experimental evidence from GFP fusion studies in C. elegans showing expression in neuronal cell bodies of specific sensory neurons. Reason: IDA evidence from PMID:11312268 directly demonstrates localization to neuronal cell bodies including AWB, AWC, AVA, AVB, AVX, BAG, and URX neurons. Supporting Evidence: PMID:11312268 Neurons expressing CePPEF include the ciliary chemosensory neurons AWB and AWC |
| GO:0005930 axoneme | IDA PMID:39550471 C. elegans PPEF-type phosphatase (Retinal degeneration C ort... | NEW | Summary: The 2024 study by Bhardwaj et al. demonstrates that PEF-1::GFP localizes specifically to the axonemal region of sensory cilia, excluded from the transition zone. This is more specific than GO:0005929 (cilium). Reason: Experimental evidence from PMID:39550471 demonstrates specific axonemal localization within cilia. This should be added as a new annotation with IDA evidence. Supporting Evidence: PMID:39550471 we found the PEF-1::GFP protein to be concentrated within the cilium, but in a region distal to the transition zone (TZ), which represents the proximal-most region of the axoneme |
| GO:0097730 non-motile cilium | IDA PMID:39550471 C. elegans PPEF-type phosphatase (Retinal degeneration C ort... | NEW | Summary: C. elegans sensory cilia are exclusively non-motile. PEF-1 localizes to these non-motile sensory cilia and is required for their proper function. Reason: PEF-1 is specifically localized to non-motile sensory cilia in C. elegans. This is more specific than the generic cilium term. Supporting Evidence: PMID:39550471 Its cilia are exclusively non-motile and found within sensory neurons at the distal ends of dendrites |
| GO:0040040 thermosensory behavior | IMP PMID:39550471 C. elegans PPEF-type phosphatase (Retinal degeneration C ort... | NEW | Summary: pef-1 mutants show severely impaired thermotaxis behavior, indicating PEF-1 is required for normal thermosensory responses. This represents a core biological process function. Reason: Experimental mutant phenotype demonstrates PEF-1 function in thermosensory behavior. AFD neuron expression supports this role. Supporting Evidence: PMID:39550471 pef-1 mutants are not able to thermotax like wild-type animals |
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Download this section (compressed HTML)Q: What are the direct substrates of PEF-1 phosphatase activity in sensory cilia?
Q: How does calcium binding to EF-hands regulate PEF-1 phosphatase activity?
Q: What is the mechanistic basis for selective requirement of PEF-1 in some sensory modalities (thermosensation, salt chemotaxis) but not others (osmosensation)?
Q: How does PEF-1 maintain ciliary microtubule integrity as suggested by TEM abnormalities?
Experiment: Identify PEF-1 substrates using phosphoproteomics in wild-type vs pef-1 mutant cilia
Hypothesis: PEF-1 dephosphorylates specific signaling proteins in sensory cilia
Type: phosphoproteomics
Experiment: Test whether PEF-1 phosphatase activity is calcium-regulated using purified protein
Hypothesis: Calcium binding to EF-hands modulates phosphatase activity
Type: in vitro enzyme assay
Experiment: Examine genetic interactions between pef-1 and ciliary signaling components (GPCRs, TRP channels, guanylate cyclases)
Hypothesis: PEF-1 functions in specific ciliary signaling pathways
Type: genetic epistasis
Experiment: Perform structure-function analysis of EF-hand domain mutations on ciliary function
Hypothesis: EF-hand calcium binding is required for PEF-1 ciliary function
Type: mutagenesis and behavioral assays
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