Gene Ontology annotation through association of InterPro records with GO terms
Annotation inferences using phylogenetic trees
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping
Translocation of lipid-linked oligosaccharides across the ER membrane requires Rft1 protein.
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Yeast Rft1 depletion blocks luminal appearance of M5GN2-PP-Dol, establishing the genetic requirement
"Here we provide evidence that yeast RFT1 encodes an evolutionarily conserved protein required for the translocation of Man5GlcNAc2-PP-Dol from the cytoplasmic to the lumenal leaflet of the ER membrane."
Human RFT1 deficiency leads to a disorder of N-linked glycosylation.
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Homozygous p.R67C causes CDG with intracellular DolPP-GlcNAc2Man5 accumulation
"A young patient diagnosed with a congenital disorder of glycosylation characterized by an intracellular accumulation of DolPP-GlcNAc(2)Man(5) was found to carry a homozygous point mutation in the RFT1 gene."
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Human RFT1 complements Deltarft1 yeast, demonstrating functional orthology
"Despite the low sequence similarity between the yeast and the human RFT1 proteins, we demonstrated both their functional orthology and the pathologic effect of the human p.R67C mutation by complementation assay in Deltarft1 yeast cells."
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Causality confirmed by rescue of patient fibroblasts with wild-type cDNA
"The causality of the RFT1 p.R67C mutation was further established by restoration of normal glycosylation profiles in patient-derived fibroblasts after lentiviral expression of a normal RFT1 cDNA."
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RFT1 loss stalls LLO assembly at the M5GN2 intermediate in yeast and human cells
"RFT1 deficiency in both yeast and human cells leads to the accumulation of incomplete DolPP-GlcNAc(2)Man(5) and to a profound glycosylation disorder in humans."
Does Rft1 flip an N-glycan lipid precursor?
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Reconstituted ER vesicles flip M5GN2-PP-Dol without Rft1
"We now show that a specific ER protein(s), but not Rft1, is required to flip Man(5)GlcNAc(2)-PP-Dol in reconstituted vesicles."
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Authors propose an accessory rather than catalytic role for Rft1
"Rft1 may have a critical accessory role in translocating Man(5)GlcNAc(2)-PP-Dol in vivo, but the Man(5)GlcNAc(2)-PP-Dol flippase itself remains to be identified."
Specific transbilayer translocation of dolichol-linked oligosaccharides by an endoplasmic reticulum flippase.
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An ER flippase activity translocates dolichol-linked oligosaccharides with substrate specificity
"Specific transbilayer translocation of dolichol-linked oligosaccharides by an endoplasmic reticulum flippase"
Suppression of Rft1 expression does not impair the transbilayer movement of Man5GlcNAc2-P-P-dolichol in sealed microsomes from yeast.
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Rft1-depleted sealed microsomes retain full M5-DLO flippase activity
"no difference was seen in the level of M5-DLO flippase activity in sealed wild type and Rft1-depleted microsomal vesicles"
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Authors conclude the in-vivo requirement is separable from transbilayer movement
"although Rft1 may play a critical role in vivo, depletion of this protein does not impair the transbilayer movement of M5-DLO in sealed microsomal fractions prepared from disrupted cells."
RFT1 deficiency in three novel CDG patients.
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Two novel missense alleles (p.K152E, p.E298K) reproduce M5-DLO accumulation and secretion defects
"The pathogenic character of the novel mutations was illustrated by the accumulation of Man(5)GlcNAc(2)-PP-dolichol and by reduced recombinant DNase 1 secretion."
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Delineates the RFT1-CDG clinical picture including sensorineural deafness
"The clinical phenotype of these patients comprised typical CDG symptoms in addition to sensorineural deafness, rarely reported in CDG patients."
Glycoprotein biosynthesis in a eukaryote lacking the membrane protein Rft1.
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Rft1-null trypanosomes are viable
"We report that TbRft1-null procyclic trypanosomes grow nearly normally."
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Flipping and N-glycosylation persist without Rft1
"They have normal steady-state levels of mDLO and significant N-glycosylation, indicating robust M5-DLO flippase activity."
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Chaperone model proposed as the alternative essential role
"rather than facilitating M5-DLO flipping, Rft1 facilitates conversion of M5-DLO to mDLO by another mechanism, possibly by acting as an M5-DLO chaperone."
A reference map of the human binary protein interactome.
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Systematic all-by-all binary Y2H map; source of the nine RFT1 IPI rows
"Here we present a human 'all-by-all' reference interactome map of human binary protein interactions, or 'HuRI'."
Rft1 catalyzes lipid-linked oligosaccharide translocation across the ER membrane.
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Purified human RFT1 in proteoliposomes translocates M5GN2-PP-Dol
"As with ScRft1, proteoliposomes reconstituted with HsRft1 showed almost 90% conversion of M5GN2 to M3GN2 after 2 h of incubation."
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The reconstituted activity is ATP-independent and Rft1-dependent
"Translocation was ATP-independent, occurred with similar kinetics for both dolichol or phytanol lipid carriers, and importantly, was dependent on addition of purified Rft1 or archaeal Agl23"
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Assays were performed in the absence of ATP
"we sought to reconstitute liposomes with purified ScRft1 or HhAgl23 in reactions that contained α1-2 mannosidase, without ATP"
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The authors frame the two-decade conflict between in-vivo genetics and in-vitro biochemistry
"Genetic studies identified Rft1 as the M5GN2-PP-Dol flippase in vivo but are at odds with biochemical data suggesting Rft1 is dispensable for flipping in vitro."
Molecular characterization of Rft1, an ER membrane protein associated with congenital disorder of glycosylation RFT1-CDG.
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Human Rft1 is a polytopic ER membrane protein with cytosolic termini and is not N-glycosylated
"We show that it is a multispanning membrane protein located in the ER, with its N and C termini facing the cytoplasm."
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The essential cellular role of Rft1 remains undetermined
"It is therefore not known what essential role Rft1 plays in N-glycosylation."
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Flipping proceeds without Rft1 in microsomes and vesicles, and one eukaryote is viable without it
"other studies indicated that Rft1 is not required for heptasaccharide lipid flipping in microsomes or unilamellar vesicles reconstituted with ER membrane proteins, nor is it required for the viability of at least one eukaryote."
Mechanism-guided mutagenesis of Rft1 to test its role as a dolichol-linked oligosaccharide scramblase in cells.
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Scrambling may be a moonlighting activity rather than the essential cellular role
"While this activity has been demonstrated in liposomes reconstituted with purified Rft1, biochemical evidence of additional M5-DLO scramblases and the viability of Rft1-null Trypanosoma brucei suggest that scrambling may be a moonlighting function of Rft1 rather than its essential cellular role."
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A portal-blocking mutant predicted to lack scramblase activity supports growth
"Strikingly, the portal-blocking mutant which is predicted to lack scramblase activity supported robust growth."
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M5-DLO binding, not scrambling, appears to be the essential requirement
"These data suggest that while M5-DLO binding is important for Rft1's essential function, scrambling activity is dispensable."
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Chaperone model restated as the leading alternative
"We speculate that Rft1's essential role may be as an M5-DLO chaperone, capturing and routing M5-DLO propitiously on the cytoplasmic side of the ER to coordinate DLO biosynthesis."
Defective RFT1 does not flip the N-glycan precursor
OpenScientist family-constraint analysis - is the substrate cavity or the lipid portal the conserved surface of the RFT1 fold?
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Across the eukaryotic RFT1 family, constraint concentrates on the central substrate cavity while the lateral lipid portal sits at or below transmembrane background
"central-cavity-lining transmembrane (TM) positions are the single most evolutionarily constrained structural class, well above the TM background, whereas lateral lipid-portal-lining positions are statistically indistinguishable from background"
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The cavity signal is not a fold-maintenance artifact - the cavity class contains no glycine or proline and is dominated by polar and charged side chains
"they are 28% charged and 47% polar, the chemistry of substrate coordination"
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The most constrained transmembrane positions form one compact pocket rather than being dispersed across the fold
"the 15 most-constrained TM residues have a mean pairwise distance of 19.2 Å vs a random-TM null of 30.1 Å"
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The requested archaeal and bacterial MOP comparison was not possible by sequence alignment
"PF04506/RFT1 has no alignable archaeal/bacterial members"
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The portal class is operationally defined on a single apparently occluded model, and no open lateral gate was detected in it
"my first (ray-tracing) portal detector found"
RFT1 side-chain orientation - resolving a conflict between two structural analyses
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E298 points toward the pore axis at 7.0 Angstrom, stable under every axis perturbation tested, corroborating the family-constraint run and refuting the earlier run's exposed outward-facing call
"E298 points inward, not outward"
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R67 is inward-facing but peripheral at 17.2 Angstrom, so inward-facing and cavity-lining are not the same thing
"R67 is inward-facing but peripheral"
OpenScientist structural analysis - do RFT1-CDG residues line the substrate cavity or the lipid portal?
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The evolved architecture of human RFT1 is a polytopic two-lobed bundle enclosing a central pore axis separable from the lipid-facing periphery, with an internal inverted-topology repeat - the MOP/MATE/MurJ alternating-access fold
"a polytopic ~12–14-TM, two-lobed helical bundle enclosing a discrete central pore axis that is geometrically separable from the lipid-facing periphery"
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The architecture assignment is model-based, not experimental
"is consistent with the MOP/MATE/MurJ two-domain architecture independently modelled for Rft1"
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A buried, inward-facing basic residue at the narrowest point of the pore axis is invariant across the family from human to fungi to Dictyostelium, marking the substrate-binding site as a deeply conserved feature of the wild-type protein rather than an artefact of any one model
"an invariant Arg across all orthologs"
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In the apo human model the innermost axis lining is net-acidic, so the cationic substrate cavity of the current mechanistic model is a property of substrate-docked predictions and not of the resting state
"the apo human model's innermost lining is net-acidic"
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No RFT1-CDG residue maps to the lateral dolichol portal
"No disease residue lines the lateral dolichol portal."
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Residue-level structural mapping cannot discriminate the transporter and chaperone models
"model, so cavity-localised disease mutations do not discriminate them."
Deep research on RFT1 function (falcon)
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Topology summary used for the ER membrane annotations
"Human RFT1 localizes throughout the ER. DeepTMHMM and experimental tagging/topology mapping indicate ~14 transmembrane spans with both N- and C-termini facing the cytosol"
Cyberian deep research on RFT1 function