[gmx-users] Re: g_lie function

[Anton Feenstra]

Oliwia Szklarczyk wrote:
> Dear Mr Feenstra,
> 
> I am writing according to Gromacs again. I want to calculate the free 
> energy
> of binding of an enzyme to ligand. I am totally new with gromacs. I want to
> use the function g_lie but i don't know how... I read in the internet that
> there should be one input .edr file. But I am supposed to do 2 mdruns for
> the ligand only and for the enzyme-ligand complex right? So I don't
> understand how come there should be one input, or maybe i should somehow
> compile the .edr files from both simulations? I would be grateful for some
> advice, as much as possible for the g_lie function.

g_lie is somewhat badly designed. It will calculate for you alpha*E_VdW 
+ beta*E_Coul. But this is only about half of what you need according to 
the 'LIE formula' of Aqvist:

delta-G = alpha*(E_VdW,bound - E_VdW,free)
	+ beta*(E_Coul,bound - E_Coul,free)

So, what you'd need to do is run g_lie twice, once for the ligand-only 
'free' simulation, and once for the enzyme-ligand complex (bound) 
simulation. Then you'd subtract the result for 'free' from that of 
'bound', yielding the same delta-G estimate as in the LIE formula above.

By the way, the last time I used g_lie, there were some problems with 
it. If I recall correctly, one parameter was used as alpha and beta, and 
the other was not used. I think this was fixed, but be sure to check!


-- 
Groetjes,

Anton
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|             |                                                       |
|  _   _  ___,| K. Anton Feenstra                                     |
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