Table 1.
Thermodynamics of solution-to-membrane partitioning of the amphitropic proteins and peptides determined by NMR, tryptophan fluorescence, and far-UV circular dichroism
| Proteins | Membranes | Methods | Membrane partition coefficient, Kx | Dissociation constants, KD, μM | nH | ΔGKx, kcal/mol |
|---|---|---|---|---|---|---|
| apo-Mb | POPC:POPG 9:1 LUV |
NMR | 170,000 ± 10,000 | 330 ± 10 | 2 ± 1 | −7.1 ± 0.1 |
| fluorescence | 180,000 ± 59,000 | 310 ± 50 (810 ± 5) | 2 ± 1 (9 ± 3) | −7.2 ± 0.1 | ||
| T | POPC:POPG 9:1 LUV |
NMR | 240,000 ± 11,000 | 230 ± 20 | 3 ± 1 | −7.4 ± 0.1 |
| fluorescence | 250,000 ± 100,000 | 220 ± 130 | 2 ± 1 | −7.4 ± 0.3 | ||
| ALO | POPC:chol 6:4 LUV |
NMR | 800,000 ± 54,000 | 70 ± 5 | 2 ± 1 | −8.1 ± 0.1 |
| fluorescence | 640,000 ± 94,000 | 90 ± 20 | 3 ± 1 | −7.9 ± 0.1 | ||
| P233 | POPC:POPG:chol 7:2:1 SUV |
NMR | 52,000 ± 1,000 | 1,000 ± 60 | 3 ± 1 | −6.4 ± 0.01 |
| fluorescence | 26,000 ± 10,000 | 2,100 ± 600 (4,100 ± 30) | 2 ± 1 (18 ± 3) | −6.0 ± 0.2 | ||
| Far-UV CD | 25,000 ± 2,000 | 2,200 ± 200 | 3 ± 1 | −6 ± 0.1 |
The table reports the membrane partition coefficient (Kx), dissociation constant (KD), Hill number (nH), and free energy (ΔGKx) values.
The thermodynamic values corresponding with the second transition of peptide/protein reorganization in membranes are reported in brackets because they do not report solution to membrane partitioning. For membrane partitioning, nH values have no biological meaning because protein membrane interaction corresponds to a change of environment (i.e., from solution to membrane) and not to a bimolecular interaction. Here, nH values help to provide a better fitting of the equation to the experimental data and to improve the estimation of the KD values.