Inhibition of Protein Phosphatase-1 by Clavosines A and B
Bibliographic record
Abstract
Site-directed mutagenesis was used to investigate the mechanism of interaction between the catalytic subunit of human protein phosphatase-1 (PP-1cgamma) and members of the calyculin family of toxins. Clavosines A and B are related to calyculins but are glycosylated with a trimethoxy rhamnose group. We provide experimental evidence implicating Tyr-134 as an important residue in PP-1cgamma that mediates interactions with the calyculins. Mutation of Tyr-134 to Phe, to prevent hydrogen bond formation, resulted in a slight increase in sensitivity of PP-1cgamma to clavosines A and B and calyculin A. In contrast, a Y134A mutant was 10-fold less sensitive to inhibition by all three inhibitors. The greatest effect on inhibition was found by substituting an Asp for Tyr-134 in the phosphatase. Clavosine B inhibited PP-1cgamma Y134D with a 310-fold decrease in potency. Clavosine A and calyculin A were also markedly poorer inhibitors of this mutant. These results suggest that a hydrogen bond between Tyr-134 and the calyculins is unlikely to be essential for inhibitor binding to the phosphatase. The clavosines and calyculin A were tested for their ability to inhibit other mutants of PP-1cgamma (including Ile-133, Val-223, and Cys-291). Our mutagenesis studies provide an experimental basis for assessing models of calyculin binding found in the literature (Lindvall, M. K., Pihko, P. M., and Koskinen, A. M. (1997) J. Biol. Chem. 272, 23312-23316; Gupta, V., Ogawa, A. K., Du, X., Houk, K. N., and Armstrong, R. W. (1997) J. Med. Chem. 40, 3199-3206; Gauss, C. M., Sheppeck, I. J., Nairn, A. C., and Chamberlain, R. (1997) Bioorg. Med. Chem. 5, 1751-1773). A new model for clavosine and calyculin A binding to PP-1c is presented that is consistent with previous structure-function experiments and which accommodates key structural features of the clavosines, including the novel rhamnose moiety.
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How this classification was reachedexpand
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".