. 2003 Jul;12(7):1395–1405. doi: 10.1110/ps.0241403

Table 4.

Contributions of α-helix propensity, hydrophobic and electrostatic interactions to coiled-coil stability

Peptide comparisons
More stable coiled-coil	Less stable coiled-coil	ΔΔG_u^obs coiled-coil (kcal mole⁻¹)	Description of stabilizing contribution	ΔΔG_u^obs per substitution (kcal mole⁻¹)	ΔΔG_u^obs corrected^d (kcal mole⁻¹)
Hybrid 2	L7A	1.44	Hydrophobic contribution of Leu (g) vs. Ala	0.74	0.74
Hybrid 2	L26A	1.38	Hydrophobic contribution of Leu (e) vs. Ala	0.69	0.69
Hybrid 2	E14A	1.06	Electrostatic and H-bond attractions uncorrected for α-helix propensity	0.53	0.75
Hybrid 2	K19A	1.39	Electrostatic and H-bond attractions uncorrected for α-helix propensity	0.70	0.70
Hybrid 2	E14A, K19A	1.08	Electrostatic and H-bond attractions uncorrected for α-helix propensity	0.54	0.76
E14A, K19A	K19A	0.45^a	Helix propensity of Ala vs. Glu (g)	0.22	—
E14A, K19A	E14A	0.00	Helix propensity of Ala vs. Lys (e)	0.00	—
K19A	K19E	1.53^b	Removal of electrostatic repulsions uncorrected for α-helix propensity	0.77	0.55
Hybrid 2	K19E	3.06^c	Removal of electrostatic repulsions and replacement with electrostatic and H-bond attractions	—	—

^a The α-helix propensity effect of E14 to A14 is calculated from the equation ΔΔG_u^obs = ([urea]_1/2(E14A, K19A) − [urea]_1/2(K19A))*(m_{E14A, K19A} + m_K19A)/2 (from Serrano and Fersht 1989).

^b The stabilizing effects of removing two electrostatic repulsions is calculated from ΔΔG_u^obs = ([urea]_1/2(K19A) − [urea]_1/2(K19E)*(m_K19A + m_K19E)/2 (from Serrano and Fersht 1989).

^c Observed values of ΔΔG_{u, coiled coil} = 3.06 kcal mole⁻¹ can be compared with the calculated corrected values from the loss of two electrostatic repulsions 2*(0.55), plus the gain of the average value for two electrostatic attractions and H-bonding 2*(0.73), = 2.56 kcal mole⁻¹.

^d ΔΔG_u^obs corrected is the ΔΔG_u^obs per substitution corrected for α-helix propensity effects. The α-helix propensity of Ala compared to Glu is 0.22 kcal mole⁻¹, which means that the stabilizing effect of an electrostatic and H-bond attraction is the ΔΔG_u^obs value of 0.54 kcal mole⁻¹ plus 0.22 kcal mole⁻¹ to give 0.76 kcal mole⁻¹.