Comparative study of substrate and product binding to the human ABO(H) blood group glycosyltransferases
Why this work is in the frame
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Bibliographic record
Abstract
The first comparative thermodynamic study of the human blood group glycosyltransferases, alpha-(1-->3)-N-acetylgalactosaminyltransferase (GTA) and alpha-(1-->3)-galactosyltransferase (GTB), interacting with donor substrates, donor and acceptor analogs, and trisaccharide products in vitro is reported. The binding constants, measured at 24 degrees C with the direct electrospray ionization mass spectrometry (ES-MS) assay, provide new insights into these model GTs and their interactions with substrate and product. Notably, the recombinant forms of GTA and GTB used in this study are shown to exist as homodimers, stabilized by noncovalent interactions at neutral pH. In the absence of divalent metal ion, neither GTA nor GTB exhibits any appreciable affinity for its native donors (UDP-GalNAc, UDP-Gal). Upon introduction of Mn(2+), both donors undergo enzyme-catalyzed hydrolysis in the presence of either GTA or GTB. Hydrolysis of UDP-GalNAc in the presence of GTA proceeds very rapidly under the solution conditions investigated and a binding constant could not be directly measured. In contrast, the rate of hydrolysis of UDP-Gal in the presence of GTB is significantly slower and, utilizing a modified approach to analyze the ES-MS data, a binding constant of 2 x 10(4) M(-1) was established. GTA and GTB bind the donor analogs UDP-GlcNAc, UDP-Glc with affinities similar to those measured for UDP-Gal and UDP-GalNAc (GTB only), suggesting that the native donors and donor analogs bind to the GTA and GTB through similar interactions. The binding constant determined for GTA and UDP-GlcNAc (approximately 1 x 10(4) M(-1)), therefore, provides an estimate for the binding constant for GTA and UDP-GalNAc. Binding of GTA and GTB with the A and B trisaccharide products was also investigated for the first time. In the absence of UDP and Mn(2+), both GTA and GTB recognize their respective trisaccharide products but with a low affinity approximately 10(3) M(-1); the presence of UDP and Mn(2+) has no effect on A trisaccharide binding but precludes B-trisaccharide binding.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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 it