Table 2.
Helix propensity measured in various systems
| Model system† (sequence) | ΔG(Gly) − ΔG(Ala), kcal mol−1 | Intercept | Slope | Correlation coefficient |
|---|---|---|---|---|
| Peptides | ||||
| RNase T1 peptide | 0.98 | (0.00)‡ | (1.00)‡ | (1.00)‡ |
| (-STAQXAAYK-) | ||||
| AK | 1.97 | 0.00 | 1.84 | 0.97 |
| (-AAKAXAAKA-) | ||||
| E4K4 | 0.74 | 0.06 | 0.70 | 0.97 |
| (-KKKXXXEEE-) | ||||
| EAK | 1.95 | −0.04 | 1.79 | 0.90 |
| (-AKEAXAKEA-) | ||||
| Host–guest | 0.35 | −0.11 | 0.35 | 0.80 |
| (HBLP or HPLG) | ||||
| AGADIR | 1.10 | −0.04 | 1.02 | 0.96 |
| (various) | ||||
| Proteins | ||||
| RNase T1 protein-21 | 0.90 | −0.02 | 0.96 | 0.98 |
| (-STAQXAAYK-) | ||||
| Barnase-32 | 0.91 | 0.19 | 0.88 | 0.88 |
| (-KSAQXLG-) | ||||
| T4 lysozyme-44 | 0.96 | −0.13 | 0.92 | 0.93 |
| (-QAAKXELDK-) | ||||
| Coiled–coil | 0.77 | 0.07 | 0.74 | 0.90 |
| (-AALEXKLQA-) |
The peptide or protein systems being compared to the RNase T1 peptide are shown along with the sequence near the substitution site (X), given as one-letter amino acid codes. For the peptide model systems, the AK data are from Baldwin’s group (16), the E4K4 data are from Kallenbach’s group (5), the EAK data are from Stellwagen’s group (23) as analyzed by Chakrabartty and Baldwin (3), the host–guest studies of Scheraga (24) and the algorithm AGADIR is from Muñoz and Serrano (25). HPLG and HBLG refer to the host, hydroxypropyl- or hydroxybutyl-l-glutamine, respectively (24). The protein models are from site 32 in barnase (22), site 44 in T4 lysozyme (18, 19) and a solvent-exposed site in a model coiled–coil peptide (26).
The intercept, slope, and correlation coefficient are derived by plotting the data from the indicated model system against the results for the RNase T1 peptide.