Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity
Annotation inferences using phylogenetic trees
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
Genome-wide YFP fluorescence complementation screen identifies new regulators for telomere signaling in human cells.
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Genome-wide BiFC screen of ~12,000 proteins against six telomeric baits; the authors caution that hits require secondary validation.
"Although PCA/BiFC does appear to be more tolerant of differences in expression, high expression levels of bait and prey may still result in false positives. Therefore, secondary screens are needed to validate the identified interactions."
Human alpha-endosulfine, a possible regulator of sulfonylurea-sensitive KATP channel: molecular cloning, expression and biological properties.
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Recombinant human alpha-endosulfine displaces glibenclamide from beta-cell membranes, inhibits cloned Kir6.2/SUR1 K-ATP currents and stimulates insulin release from MIN6 cells.
"The recombinant protein displaces binding of the sulfonylurea [3H]glibenclamide to beta cell membranes, inhibits cloned KATP channel currents, and stimulates insulin secretion."
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The channel effect was selective for Kir6.2/SUR1 over Kir1.1 but the interacting subunit could not be identified.
"We therefore cannot exclude the alternative possibility that α-endosulfine binds to Kir6.2 and thereby displaces glibenclamide binding to SUR1."
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ENSA lacks a signal peptide and is predicted to be intracellular, yet blocked currents from either side of the membrane.
"On the other hand, we observed that α-endosulfine blocked K ATP currents when applied both intracellularly and extracellularly, and it stimulated insulin secretion when added to the extracellular solution."
MASTL phosphorylates ENSA
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MASTL phosphorylates ENSA on Ser67, activating it as a PP2A-B55 inhibitor.
"MASTL (GWL) activates ENSA by phosphorylating it on serine residue S67 (Mochida et al. 2010, Gharbi-Ayachi et al. 2010)."
Greatwall phosphorylates an inhibitor of protein phosphatase 2A that is essential for mitosis.
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Greatwall-phosphorylated Ensa is the mitotic PP2A-B55δ inhibitor in Xenopus egg extracts.
"We report that inhibition of PP2A-B55δ results from a small protein, known as α-endosulfine (Ensa), that is phosphorylated in mitosis by the protein kinase Greatwall (Gwl). This converts Ensa into a potent and specific inhibitor of PP2A-B55δ."
The substrate of Greatwall kinase, Arpp19, controls mitosis by inhibiting protein phosphatase 2A.
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Both Arpp19 and α-endosulfine are Gwl substrates that inhibit PP2A when phosphorylated, but Arpp19 is the limiting inhibitor at mitotic entry in Xenopus egg extracts.
"Although both proteins can inhibit PP2A, endogenous Arpp19, but not α-Endosulfine, is responsible for PP2A inhibition at mitotic entry in Xenopus egg extracts."
The BEG (PP2A-B55/ENSA/Greatwall) pathway ensures cytokinesis follows chromosome separation.
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In HeLa cells ENSA, not ARPP19, is the major MASTL substrate.
"Given that ARPP19 was not detected (Figure S3E) and that ARPP19 siRNA had little effect (Figure 4B), ENSA is the major target of Greatwall/MASTL in these cells."
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PP2A-B55 is the phosphatase that dephosphorylates ENSA Ser67 in human cell extracts.
"Furthermore, the removal of the PP2A regulatory subunits PPP2R2A–PPP2R2D stabilized both PRC1 pT481 and ENSA phosphorylation (Figure 4B), indicating that PP2A-B55 is the ENSA phosphatase in this system."
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The ENSA/Greatwall timer delays PP2A-B55 reactivation and PRC1 dephosphorylation so that cytokinesis follows chromosome separation.
"Removal of the ENSA/Greatwall (EG) timer module eliminates this second threshold, as well as associated delay in PRC1 dephosphorylation and initiation of cytokinesis, by uncoupling PP2A-B55 from Cdk1-cyclin B activity."
Greatwall-phosphorylated Endosulfine is both an inhibitor and a substrate of PP2A-B55 heterotrimers.
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Phospho-endosulfine inhibits PP2A-B55 by unfair competition - it binds far more avidly and is dephosphorylated far more slowly than other substrates.
"As the name suggests, during M phase PP2A-B55's attention is diverted to pEndos, which binds much more avidly and is dephosphorylated more slowly than other substrates."
Ensa controls S-phase length by modulating Treslin levels.
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ENSA knockdown in human cells extends S phase and lowers Treslin levels; Treslin overexpression rescues.
"Unexpectedly, Ensa knockdown promotes a dramatic extension of S phase associated with a lowered density of replication forks. Notably, Ensa depletion results in a decrease of Treslin levels, a pivotal protein for the firing of replication origins."
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Nuclear localisation of ENSA increases in S phase.
"In contrast, nuclear localisation of Ensa was significantly increased in S-phase cells suggesting that Ensa is relocalised into the nucleus during DNA replication."
The Cell Cycle Checkpoint System MAST(L)-ENSA/ARPP19-PP2A is Targeted by cAMP/PKA and cGMP/PKG in Anucleate Human Platelets.
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ENSA is present and phosphorylated in anucleate human platelets; only the MASTL-site-phosphorylated form inhibits PP2A.
"Our data also established that both MASTL- and PKA/PKG-phosphorylated ENSA/ARPP19 are PP2A substrates, whereas only MASTL-phosphorylated ENSA/ARPP19 are PP2A inhibitors."
Interaction mechanism of endogenous PP2A inhibitor protein ENSA with PP2A.
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Human ENSA is intrinsically disordered with three transient helices and binds PP2A mainly via the A subunit in vitro.
"ENSA was observed to interact PP2A mainly via A-subunit, as the affinity with the A-subunit is significantly stronger than with any of the B56 subunits."
Regulation of α-endosulfine, an inhibitor of protein phosphatase 2A, by multisite phosphorylation.
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The conserved Ser67-containing middle region of ENSA binds PP2A-B55 at the B55/C subunit interface over the catalytic centre.
"Structural analyses revealed that the most-conserved middle region of ENSA containing S67 physically interacts with PP2A-B55 at the interface of the B55 and C subunits, where the catalytic centre of PP2A is located."
ARPP-16 Is a Striatal-Enriched Inhibitor of Protein Phosphatase 2A Regulated by Microtubule-Associated Serine/Threonine Kinase 3 (Mast 3 Kinase).
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There is no evidence that ENSA is extracellular; the family's function appears limited to control of PP2A.
"However, there is no evidence that ENSA is found extracellularly."
Somatostatin-evoked Aβ catabolism in the brain: Mechanistic involvement of α-endosulfine-K(ATP) channel pathway.
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In mouse brain ENSA acts downstream of somatostatin as a negative regulator of neprilysin via a SUR1/Kir6.2 K-ATP channel.
"Here, we identified α-endosulfine (ENSA), an endogenous ligand of the ATP-sensitive potassium (KATP) channel, as a negative regulator of NEP downstream of SST signaling."
Deep research report for ENSA (human), Falcon provider
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Summarises the phospho-ENSA/PP2A-B55 unfair-substrate mechanism and grades the K-ATP channel literature as provisional.
"Phosphorylated ENSA then binds PP2A-B55 as a high-affinity inhibitory substrate. Its phosphoserine occupies the phosphatase catalytic machinery, but dephosphorylation is unusually slow relative to ordinary substrates."
UniProt entry O43768 (ENSA_HUMAN)