Table 2.

The change in free energy for different noncovalent interactions

Analog comparison
More stable	Less stable	Description of contribution in each comparisona	Number of substitutions or interactions per coiled-coilb	ΔΔGu per coiled-coilc (kcal•mol−1)	ΔΔGu per substitution or interactiond (kcal•mol−1)
N14A,N15A,S23A	N14A,N15A	Contribution of Ala in place of Ser in the hydrophobic core	2	0.4	0.2
N14A,N15A,S23L	N14A,N15A	Contribution of Leu in place of Ser in the hydrophobic core	2	2.6	1.3
N14A,N15A,S23L	N14A,N15A,S23A	Contribution of Leu in place of Ala in the hydrophobic core	2	2.2	1.1
S19A,S21A,S23L	S23L	Contribution of Ala in place of Ser (increase α-helical propensity)	4	0.5	0.1
N14A,N15A,S23L	S23L	Destabilizing effect of the NN motif (includes N → A propensity effect)	2	1.8	0.9
N14A,N15A,S23L	S19A,S21A,S23L	Net destabilizing effect of the NN motif	2	1.3	0.6
N14A,N15A,S23L	N14A,S23L	Contribution of single Asn(N15) → Ala substitution	2	0.0	0.0
N14A,N15A,S23L	N15A,S23L	Contribution of single Asn(N14) → Ala substitution	2	−0.2	−0.1
N14A,S23L	S23L	Destabilizing effect of the NN motif (includes N → A propensity effect)	2	1.8	0.9
N15A,S23L	S23L	Destabilizing effect of the NN motif (includes N → A propensity effect)	2	2.0	1.0

^a Physical description of the effects of substitution(s) on coiled-coil stability.

^b Number of interactions in a two-stranded α-helical coiled-coil; there are two identical polypeptide chains that are joined by a disulfide bridge in our cassette model.

^c The relative change of the free energy of unfolding in the coiled-coil due to the substitution(s).

^d The relative change of the free energy of unfolding per substitution or interaction. This is obtained by dividing the ΔΔG_u/coiled-coil by the number of substitution(s) or interaction(s) in the coiled-coil, and rounded off to the nearest 0.1 kcal/mol.