Cloning and functional characterization of <i>Xenopus laevis</i> facilitated hexose transporters GLUT2 and GLUT4 (XL‐GLUT2, XL‐GLUT4).
Bibliographic record
Abstract
RT‐PCR was used to clone members of the facilitated hexose transporter gene family (SLC2A) from Xenopus oocyte total RNA. Gene specific primers were designed using the NIH Xenopus Gene Collection. We have identified two Xenopus GLUT sequences, XL‐GLUT2 and XL‐GLUT4 (gene accession numbers EF102088 & EF102089 ) which have 62% & 69% identity and 78% & 83% similarity with their human orthologues, respectively. Functional characterization of XL‐GLUT2 shows that this protein transports 2‐deoxyglucose > galactose > glucose > 3‐O‐methyl glucose >> fructose. In contrast, hGLUT2 has an equal affinity for both glucose and fructose (Km > 20mM) while XL‐GLUT2 has a much higher affinity, for glucose alone with a Km of 2.5 ± 0.5 mM. Sequence alignment and comparison of the Xenopus and human transporters in the region of their predicted 7th transmembrane helix shows that several motifs are highly conserved, in particular the QLS and the NXV/I sequences. This latter hydrophobic motif has previously been found to influence substrate specificity in human GLUTs. hGLUT2 has the motif NGI which when mutated to NGV results in an almost complete loss of fructose transport, however, the Xenopus WT protein has very low fructose transport capacity, yet still has the NGI motif. This suggests that this hydrophobic region found near the exofacial opening of the transport pore of GLUT proteins is not the sole determinant of substrate specificity.
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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) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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".