[gmx-users] Fe(II) at active site

[X.Periole]

> During the simulation of protein with Fe (II) ligating 
>with 2 His and 1
> Asp residues at active site, I set every thing right 
>including Kb value
> but failed to deprotonate NE2 atoms of 2 His residues 
>ligating that
>Fe(II). 

What do you mean by failed ? This should not be a problem.
You can choose the protonation state of a his ... check
the ffXXX.rtp file.

> After 2ns simulation run, the average pdb 
>structure shows that
> the flip of His ring out from Fe (II), but the 
>Asp-oxygen moved much
> closer to Fe (II) than its original position. If I 
>compute RMSF for Fe
> (II), showing value of "0" through out the simulation 
>run.  The RMSF "0"
> indicates Fe (II) originally retained in its position, 

0 fluctuations at all !!! You fixed its position or
something ? That does not seems right !!

>but the ligating
> His flipped and Asp as a single residue held the Fe (II) 
>at its original
> position. So now please tell me whether this simulation 
>is valid?

The simulation that you discribe does not seem to be
a good representation of your system ...

XAvier