Thermodynamic Characterization of the Exchange of Detergents and Amphipols at the Surfaces of Integral Membrane Proteins
Bibliographic record
Abstract
The aggregation of integral membrane proteins (IMPs) in aqueous media is a significant concern for mechanistic investigations and pharmaceutical applications of this important class of proteins. Complexation of IMPs with amphiphiles, either detergents or short amphiphilic polymers known as amphipols (APols), renders IMPs water-soluble. It is common knowledge that IMP-detergent complexes are labile, while IMP-APol complexes are exceptionally stable and do not dissociate even under conditions of extreme dilution. To understand the thermodynamic origin of this difference in stability and to guide the design of new APols, we have studied by isothermal titration calorimetry (ITC) the heat exchanges during two reciprocal processes, the "trapping" of detergent-solubilized IMPs in APols and the "stripping" of IMP-APol complexes by detergents, using two IMPs (the transmembrane domain of porin OmpA from Escherichia coli and bacteriorhodopsin from Halobium salinarium), two APols [an anionic polymer derived from acrylic acid (A8-35) and a cationic phosphorylcholine-based polymer (C22-43)], and two neutral detergents [n-octyl thioglucoside (OTG) and n-octyltetraethylene glycol (C(8)E(4))]. In the presence of detergent, free APols and IMP-APol complexes form mixed particles, APol-detergent and IMP-APol-detergent, respectively, according to the regular mixing model. Diluting IMP-APol-detergent complexes below the critical micellar concentration (CMC) of the detergent triggers the dispersion of detergent molecules as monomers, a process characterized by an enthalpy of demicellization. The enthalpy of APol <--> detergent exchange on the hydrophobic surface of IMPs is negligibly small, an indication of the similarity of the molecular interactions of IMPs with the two types of amphiphiles. The enhanced stability against dilution of IMP-APol complexes, compared to IMP-detergent ones, originates from the difference in entropy gain achieved upon release in water of a few APol molecules (in the case of IMP-APol complexes) or several hundred detergent molecules (in the case of IMP-detergent complexes). The data account both for the stability of IMP-APols complexes in the absence of detergent and for the ease with which detergents displace APols from the surface of proteins.
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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".