[gmx-users] DelG of LJ Transformation Negative Glu--->Ala Mutation

[Sai Kumar Ramadugu]

Hi Gmx Community,
I am doing Glutamate to Alanine mutation in presence and absence of a
ligand.
The Coulomb transformation is yielding the following results:
Glu--->Ala + ligand = 790.109 kJ/mol
Glu--->Ala + no ligand = 787.33 kJ/mol

During the LJ transformation

Glu--->Ala + ligand = - 24.87 kJ/mol
Glu--->Ala + no ligand = - 12.4403


The reason I am asking this is because in experiments, the Glu--->Ala
mutation yields a positive deldelG but in TI approach, I am getting a
negative deldelG. The major contribution is from the LJ transformation.
With the above values, the deldelG from TI approach is -9.65 kJ/mol

Is it possible to have a negative deldelG for a mutation like Glutamate
(which is charged) to Alanine (which is neutral)?

If it is system dependent and you need more information than what provided
in this email, I will add in happily. But I am just curious to know your
opinions.

Regards
Sai