NEK3 (NimA-related protein kinase 3, AT5G28290) is a serine/threonine protein kinase belonging to the plant NIMA-related kinase (NEK) family, one of seven members in Arabidopsis. The N-terminal half (residues 4-258) contains a canonical protein kinase domain with ATP-binding and catalytic sites, while the C-terminal half (residues ~258-568) is a regulatory region with disordered segments. GFP-tagged NEK3 localizes to microtubules in a similar manner to NEK6, the best-characterized plant NEK (PMID:21605211). The Arabidopsis NEK family broadly regulates microtubule organization, with NEK6 shown to phosphorylate beta-tubulin and destabilize cortical microtubules to control directional cell expansion. However, NEK3 itself is poorly characterized: no nek3 mutant phenotype, no specific substrates, and no specific interaction partners have been published. UniProt annotates NEK3 function as "May be involved in plant development processes" based on family-wide expression analysis (PMID:17886359).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004674 protein serine/threonine kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Protein serine/threonine kinase activity is inferred by phylogenetic analysis (IBA) from characterized NEK family members. NEK3 contains a canonical protein kinase domain (IPR000719, residues 4-258) with conserved ATP-binding and Ser/Thr kinase active site motifs. The related NEK6 has demonstrated kinase activity in vitro, phosphorylating beta-tubulin. This annotation is well-supported by domain architecture and family membership. Reason: Ser/Thr kinase activity is the core molecular function of the NEK family. The domain architecture (kinase domain, ATP-binding site, catalytic residues) strongly supports this annotation. The closely related NEK6 has demonstrated kinase activity experimentally. Supporting Evidence: PMID:21605211 NEK6 directly binds to microtubules in vitro and phosphorylates Ξ²-tubulin PMID:17886359 NIMA-related kinases (Neks) are a family of serine/threonine kinases file:ARATH/NEK3/NEK3-deep-research-bioreason-sft.md [BioReason correctly identifies canonical bilobal catalytic module with ATP-binding P-loop and serine/threonine kinase active site] file:ARATH/NEK3/NEK3-deep-research-falcon.md Plant NEKs (including AtNek3) are described as **serine/threonine protein kinases** with a conserved **N-terminal catalytic kinase domain** and a longer **C-terminal non-catalytic extension**, consistent with the UniProt domain calls (protein kinase domain; ATP-binding and activation-segment motifs). file:ARATH/NEK3/NEK3-deep-research-falcon.md AtNek3 is a **NIMA-related serine/threonine protein kinase** by sequence/domain architecture and family definition; reaction class is ATP-dependent phosphorylation of protein substrates (EC 2.7.11.1), but **substrate identity and specificity remain unknown** for AtNek3 based on retrieved evidence. |
| GO:0004672 protein kinase activity | IEA GO_REF:0000002 | MODIFY | Summary: Protein kinase activity is inferred from InterPro domain matches (IPR000719 protein kinase domain, IPR008271 Ser/Thr kinase active site). This is a more general parent term of protein serine/threonine kinase activity (GO:0004674). Since the more specific Ser/Thr kinase annotation is already present via IBA, this general term is redundant. Reason: The more specific term GO:0004674 (protein serine/threonine kinase activity) is already annotated and better represents the function. NEK kinases are Ser/Thr-specific kinases, so the general protein kinase activity term should be replaced with the specific one. Proposed replacements: protein serine/threonine kinase activity |
| GO:0004674 protein serine/threonine kinase activity | IEA GO_REF:0000003 | ACCEPT | Summary: This is a duplicate annotation from EC number mapping (EC:2.7.11.1). The same term is already annotated via IBA (GO_REF:0000033) with stronger evidence. This EC-based IEA annotation is redundant but not incorrect. Reason: The annotation is correct based on the EC number assignment. Although redundant with the IBA annotation, it provides independent supporting evidence from a different source (enzyme classification). |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | ACCEPT | Summary: ATP binding is inferred from InterPro domain matches (IPR000719 protein kinase domain, IPR017441 ATP binding site). The protein kinase domain contains a conserved glycine-rich P-loop (residues 10-18) and a conserved lysine (K33) for ATP coordination. ATP binding is required for kinase catalytic activity. Reason: ATP binding is a fundamental requirement for kinase activity. The domain architecture clearly supports this annotation, with conserved ATP-binding motifs identified by PROSITE and InterPro. Supporting Evidence: file:ARATH/NEK3/NEK3-deep-research-falcon.md Plant NEKs (including AtNek3) are described as **serine/threonine protein kinases** with a conserved **N-terminal catalytic kinase domain** and a longer **C-terminal non-catalytic extension**, consistent with the UniProt domain calls (protein kinase domain; ATP-binding and activation-segment motifs). |
| GO:0106310 protein serine kinase activity | IEA GO_REF:0000116 | MODIFY | Summary: Protein serine kinase activity is inferred from the Rhea reaction mapping (RHEA:17989) for the catalytic activity L-seryl-[protein] + ATP = O-phospho-L-seryl-[protein] + ADP + H+. This is a more specific child term of GO:0004674 that restricts the substrate to serine residues only. NEK kinases are dual serine/threonine kinases, so the more general GO:0004674 is more appropriate. Reason: NEK kinases phosphorylate both serine and threonine residues (UniProt lists both catalytic activities). The serine-only term is overly restrictive. The broader serine/threonine kinase activity term better captures the function. Proposed replacements: protein serine/threonine kinase activity |
| GO:0005634 nucleus | ISM GO_REF:0000122 | REMOVE | Summary: Nuclear localization is predicted by TAIR computational methods (AtSubP analysis). However, GFP-tagged NEK3 localizes to microtubules (PMID:21605211), not the nucleus. The related NEK6 localizes to cortical microtubules. There is no experimental evidence supporting nuclear localization for any Arabidopsis NEK family member. Reason: The ISM prediction of nuclear localization contradicts the only direct experimental evidence: GFP-NEK3 localizes to microtubules (Motose et al. 2011). NEK family members in plants are cytoplasmic and microtubule-associated. The computational prediction is likely incorrect. Supporting Evidence: file:ARATH/NEK3/NEK3-deep-research-falcon.md No AtNek3-specific experimental subcellular localization was identified in the gathered evidence. Localization data in the available literature concern other plant NEKs such as PNek1, not AtNek3. |
| GO:0005886 plasma membrane | ISM GO_REF:0000122 | REMOVE | Summary: Plasma membrane localization is predicted by TAIR computational methods (AtSubP analysis). NEK3 has no transmembrane domains and no lipid modification signals. GFP-tagged NEK3 localizes to microtubules (PMID:21605211). While cortical microtubules are near the plasma membrane, the protein itself is a soluble kinase associated with microtubules, not the plasma membrane. Reason: The ISM prediction of plasma membrane localization is not supported by experimental evidence. GFP-NEK3 localizes to microtubules (Motose et al. 2011). The protein lacks transmembrane domains or membrane-targeting signals. Cortical microtubule proximity to the plasma membrane may confound computational predictions, but the protein is microtubule-associated, not membrane-associated. Supporting Evidence: file:ARATH/NEK3/NEK3-deep-research-falcon.md No AtNek3-specific experimental subcellular localization was identified in the gathered evidence. Localization data in the available literature concern other plant NEKs such as PNek1, not AtNek3. |
| GO:0005874 microtubule | IDA PMID:21605211 NIMA-related kinases 6, 4, and 5 interact with each other to... | NEW | Summary: GFP-tagged NEK3 localizes to microtubules in Arabidopsis cells, in a similar manner to the well-characterized NEK6. This is direct experimental evidence from fluorescence microscopy. The related NEK6 directly binds microtubules in vitro. Note: independent falcon deep research did not retrieve this NEK3-specific localization result in its corpus (it noted localization data for other plant NEKs such as PNek1), reflecting a coverage limitation rather than a contradiction; the IDA from Motose et al. 2011 remains the strongest direct evidence and is retained. Reason: This annotation is supported by direct experimental observation of GFP-NEK3 localization to microtubules (Motose et al. 2011). This is the most informative cellular component annotation for NEK3 and should be added. Evidence type is IDA based on fluorescence microscopy of GFP fusion protein. Supporting Evidence: PMID:21605211 Here, we analyze the function of NEK6 and other members of the NEK family with regard to epidermal cell expansion and cortical microtubule organization |
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Download this section (compressed HTML)Q: What is the phenotype of nek3 single mutants and nek3/nek6 double mutants? Do they show microtubule organization defects similar to nek6/ibo1?
Suggested experts: Hiroyasu Motose, Taku Takahashi
Q: Does NEK3 phosphorylate beta-tubulin like NEK6, or does it have distinct substrates? Can NEK3 form heterodimers with NEK4, NEK5, or NEK6?
Suggested experts: Hiroyasu Motose, Shogo Takatani
Q: Is NEK3 expressed in pollen or pollen tubes? Is there functional redundancy among NEK family members in specific tissues?
Suggested experts: Frederic Vigneault
Experiment: Generate nek3 T-DNA insertion mutants and analyze cortical microtubule organization using fluorescent tubulin markers. Compare single nek3 mutants with nek3/nek6, nek3/nek4, and nek3/nek5 double mutants for cell expansion defects, trichome morphology, and sensitivity to microtubule inhibitors (propyzamide, taxol).
Hypothesis: NEK3 has overlapping function with other NEK family members in regulating cortical microtubule organization
Type: reverse genetics
Experiment: Express and purify recombinant NEK3 kinase domain. Test in vitro kinase activity using beta-tubulin and known microtubule-associated proteins as substrates. Compare substrate specificity with NEK6.
Hypothesis: NEK3 phosphorylates beta-tubulin or other microtubule-associated proteins
Type: in vitro biochemistry
Experiment: Perform bimolecular fluorescence complementation (BiFC) or co-immunoprecipitation experiments to test pairwise interactions between NEK3 and NEK4, NEK5, NEK6, and NEK7. Compare interaction patterns with the known NEK6-NEK4 and NEK6-NEK5 interactions.
Hypothesis: NEK3 forms heterodimeric complexes with other NEK family members
Type: protein-protein interaction
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