Falcon (Edison Scientific) deep research report: Functional Annotation of Rat Uggt1 (UGGT1; UniProt Q9JLA3)
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UGGT1 is an ER luminal glycoprotein-folding sensor that reglucosylates N-linked glycans on non-native glycoproteins, acting as the central quality-control enzyme of the calnexin/calreticulin cycle.
"a ~170 kDa **endoplasmic reticulum (ER) luminal** glycoprotein-folding sensor and quality-control enzyme that catalyzes reglucosylation of N-linked glycans on non-native glycoproteins."
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UGGT1 transfers glucose from UDP-glucose onto deglucosylated N-glycans, converting Man9GlcNAc2 to Glc1Man9GlcNAc2, the tag recognized by lectin chaperones.
"UGGT1 converted **Man9GlcNAc2 → Glc1Man9GlcNAc2** on MHC I, which is the canonical “tag” for lectin-chaperone binding in the ER."
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Catalysis requires Ca2+ coordinated by a DxD motif in the catalytic site.
"UGGT1 catalytic activity requires **Ca2+**, coordinated by a **DxD motif** in the catalytic site"
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UGGT1 is a conformation sensor that preferentially recognizes non-native glycoproteins with exposed hydrophobic regions.
"UGGT1 is a conformation sensor: it preferentially acts on proteins that are **non-native** and can prefer clients with **exposed hydrophobic regions**, consistent with recognition of misfolded/partially folded surfaces rather than fully folded proteins."
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UGGT1 functions within the calnexin/calreticulin (CNX/CRT) cycle, reglucosylating misfolded glycoproteins so they rebind lectin chaperones and avoid premature ER exit.
"UGGT1’s primary pathway role is within the **N-glycan-dependent lectin chaperone system** (CNX/CRT cycle) that retains and refolds non-native glycoproteins."
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UGGT1-mediated reglucosylation can delay entry into glycoprotein ERAD, competing with EDEM/mannose-trimming degradation pathways in a tug-of-war over glycoprotein fate.
"UGGT1-mediated reglucosylation can **delay entry into gpERAD**, competing with EDEM/mannose trimming that promotes degradation."
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UGGT1 is the dominant cellular glucosyltransferase of this system and shows preference toward large plasma-membrane proteins.
"UGGT1 was the **dominant** cellular glucosyltransferase in that study and showed preference toward **large plasma-membrane proteins**, while UGGT2 favored smaller soluble lysosomal proteins"
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UGGT1 forms a stable complex with the selenoprotein SELENOF (SEP15), a proposed redox-active cochaperone.
"UGGT1 forms a stable complex with the selenoprotein **SEP15/SELENOF**, which is proposed to act as a **redox-active cochaperone** in ER folding surveillance."
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UGGT1 is an ER-resident luminal enzyme of the early secretory pathway.
"UGGT1 is described across multiple mammalian studies as **ER-localized/ER-resident** and operating in the **ER lumen** as part of ER protein quality control and early secretory pathway surveillance."
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UGGT1 is widely conceptualized as an ER gatekeeper / folding sensor that enforces quality control of the secretory proteome via glycan reglucosylation.
"UGGT1 is widely conceptualized as an ER “**gatekeeper**” or “folding sensor” that enforces quality control of the secretory proteome via glycan reglucosylation"