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Table I.

Energetic decomposition for KcsA and KcsA-G77AD

  KcsA KcsA-G77AD 
 Δμex(S) −15.7 −10.0 
 ΔWlocal −15.8 −9.9 
 TΔsex 1.3 −1.1 
 TΔslocalex 2.1 4.7 
Ion–site Δεlocal −21.0 0.8 
Ion–medium Δεm 2.2 −20.1 
Site–site ΔUs 7.3 −6.0 
Site–medium ΔUs-m −2.9 14.5 
Medium–medium ΔUm 0.0 −0.3 
Fluctuation (total) Δμflucex 3.1 9.3 
Fluctuation (local) ΔWlocal,flucex 5.2 −10.7 
  KcsA KcsA-G77AD 
 Δμex(S) −15.7 −10.0 
 ΔWlocal −15.8 −9.9 
 TΔsex 1.3 −1.1 
 TΔslocalex 2.1 4.7 
Ion–site Δεlocal −21.0 0.8 
Ion–medium Δεm 2.2 −20.1 
Site–site ΔUs 7.3 −6.0 
Site–medium ΔUs-m −2.9 14.5 
Medium–medium ΔUm 0.0 −0.3 
Fluctuation (total) Δμflucex 3.1 9.3 
Fluctuation (local) ΔWlocal,flucex 5.2 −10.7 

The eight carbonyl ligands comprise the local site. We consider the water molecules in the S1 and S3 sites adjoining the S2 site as the medium. Δμex(S) and ΔWlocal are obtained using thermodynamic integration. The selectivity in the KcsA system is 5.0 kcal/mol considering the site plus the medium, and it is 4.9 kcal/mol for the eight-carbonyl model. Fluctuation (total), the fluctuation contribution for the site plus two-water system; Fluctuation (local), the fluctuation contribution for the site alone. Note that these values are comparable to the selectivity free energy. All values are in kcal/mol.

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