The Energetics of Streptococcal Enolase Octamer Formation: The Quantitative Contributions of the Last Eight Amino Acids at the Carboxy-Terminus
Bibliographic record
Abstract
The enolase produced by Streptococcus pyogenes is a homo-octamer whose overall shape resembles that of a donut. The octamer is best described as a tetramer of dimers. As such, it contains two types of interfaces. The first is common to almost all enolases as most enolases that have been studied are dimers. The second is unique to the octamers and includes residues near the carboxy-terminus. The primary sequence of the enolase contains 435 residues with an added 19 as an N-terminal hexahistine tag. We have systematically truncated the carboxy-terminus, individually removing the first 8 residues. This gave rise to a series of eight structures containing respectively, 435, 434, 433, 432, 431, 430, 429 and 427 residues. The truncations cause the protein to gradually dissociate from octamers to enzymatically inactive monomers with very small amounts of intermediate tetramers and dimers. We have evaluated the contributions of the missing residues to the monomer/octamer equilibrium using a combination of analytical ultracentrifugation and activity assays. For the dissociation reaction, octamer <== ==> 8 monomer truncation of all eight C-terminal residues resulted in a diminution in the standard Gibbs energy of dissociation of about 59 kJ/mole of octamer relative to the full length protein. Considering that this change is spread over eight subunits, this translates to a change in standard Gibbs interaction energy of less than 8 kJ/mole of monomer distributed over the eight monomers. The resulting proteins, containing 434, 433, 432, 431, 430, 429 and 427 residues per monomer, showed intermediate free energies of dissociation. Finally, three other mutations were introduced into our reference protein to establish how they influenced the equilibrium. The main importance of this work is it shows that for homo-multimeric proteins a small change in the standard Gibbs interaction energy between subunits can have major physiological effects.
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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 | 0.001 |
| 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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".