Cloning and expression of a novel UDP-GlcNAc:α-d-mannoside β1,2-N-acetylglucosaminyltransferase homologous to UDP-GlcNAc:α-3-d-mannoside β1,2-N-acetylglucosaminyltransferase I
Bibliographic record
Abstract
A TBLASTN search with human UDP-GlcNAc:alpha-3-d-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GnT I; EC 2.4.1.101) as a probe identified human and mouse Unigenes encoding a protein similar to human GnT I (34% identity over 340 amino acids). The recombinant protein converted Man(alpha1-6)[Man(alpha1-3)]Man(beta1-)O-octyl to Man(alpha1-6)[GlcNAc(beta1-2)Man(alpha1-3)]Man(beta1-)O-octyl, the reaction catalysed by GnT I. The enzyme also added GlcNAc to Man(alpha1-6)[GlcNAc(beta1-2)Man(alpha1-3)]Man(beta1-)O-octyl (the substrate for beta-1,2-N-acetylglucosaminyltransferase II), Man(alpha1-)O-benzyl [with K(m) values of approximately 0.3 and >30 mM for UDP-GlcNAc and Man(alpha1-)O-benzyl respectively] and the glycopeptide CYA[Man(alpha1-)O-T]AV (K(m) approximately 12 mM). The product formed with Man(alpha1-)O-benzyl was identified as GlcNAc(beta1-2)Man(alpha1-)O-benzyl by proton NMR spectroscopy. The enzyme was named UDP-GlcNAc:alpha-d-mannoside beta-1,2-N-acetylglucosaminyltransferase I.2 (GnT I.2). The human gene mapped to chromosome 1. Northern-blot analysis showed a 3.3 kb message with a wide tissue distribution. The cDNA has a 1980 bp open reading frame encoding a 660 amino acid protein with a type-2 domain structure typical of glycosyltransferases. Man(beta1-)O-octyl, Man(beta1-)O-p-nitrophenyl and GlcNAc(beta1-2)Man(alpha1-6)[GlcNAc(beta1-2)Man(alpha1-3)]Man(beta1-4)GlcNAc(beta1-4)GlcNAc(beta1-)O-Asn were not acceptors, indicating that GnT I.2 is specific for alpha-linked terminal Man and does not have N-acetylglucosaminyltransferase III, IV, V, VII or VIII activities. CYA[Man(alpha1-)O-T]AV was between three and seven times more effective as an acceptor than the other substrates, suggesting that GnT I.2 may be responsible for the synthesis of the GlcNAc(beta1-2)Man(alpha1-)O-Ser/Thr moiety on alpha-dystroglycan and other O-mannosylated proteins.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".