Table 1. Energetic cost of Trp/Tyr/Phe mutations of OmpX compared with known scales.

Residue position in OmpX		ΔΔ$G_{\text{U}}^0$ [kcal mol−1]a
76	140	WWint	WWoct	Aroint	OmpX
W	W	0.0	0.0	0.0	0.0
F	W	0.7	0.4	0.2	0.2
Y	W	0.9	1.4	1.1	− 0.4b
W	F	0.7	0.4	0.2	0.4
W	Y	0.9	1.4	1.1	0.4

^a $\Delta \Delta G_{\text{U}}^0=\Delta G_{\text{U},\text{WT}}^0-\Delta G_{\text{U},\text{mutant}}^0.\Delta \Delta G_{\text{U}}^0$ calculated for the transfer of tryptophan, tyrosine, or phenylalanine from interface to water (Wimley-White interface scale, WW_int [33]), octanol to water (Wimley-White octanol scale, WW_oct [40]), and interface to water (aromatic side chain transfer free energy, Aro_int [10]).

^bResidue substitution calculated to be destabilizing from known energetics scales; a stabilizing effect is seen as an exception in the case of OmpX.