Structural Characterization of Type II Dockerin Module from the Cellulosome of <i>Clostridium thermocellum</i>: Calcium-Induced Effects on Conformation and Target Recognition
Bibliographic record
Abstract
The assembly of a functional cellulose-degrading complex termed the cellulosome involves two specific calcium-dependent cohesin-dockerin interactions: type I and type II. Extensive structural and mutagenesis studies have been performed on the type I modules and their interaction in an attempt to identify the underlying molecular determinants responsible for this specificity. However, very little structural information exists for the type II interaction. We have performed a variety of biophysical studies on the type II dockerin-X-module modular pair (DocX), which comprises the C-terminal region of cellulosomal scaffoldin subunit from Clostridium thermocellum, to determine the effect of calcium on its structure and interaction with type II cohesin. Our results indicate that calcium binding to type II dockerin occurs with an apparent dissociation constant (K(d)) of 7 microM, induces stable secondary and tertiary structure, and leads to the exposure of a hydrophobic surface. Calcium binding also results in the homodimerization of DocX. Analytical ultracentrifugation experiments indicate that the DocX homodimer has an elongated shape and a K(d) of approximately 40 microM. However, addition of the SdbA type II cohesin binding partner led to the dissociation of the DocX homodimer and to the formation of a 1:1 heterodimer. We propose that the exposed hydrophobic surface forms, at least in part, the type II cohesin-binding site, which in the absence of cohesin results in the dimerization of DocX.
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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) | 0.000 | 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 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".