# Zinc displacement and coordination

**URL:** <https://gromacs.bioexcel.eu/t/zinc-displacement-and-coordination/6496>\
**Category:** User discussions\
**Created:** [May 26, 2023, 8:22am UTC](https://gromacs.bioexcel.eu/t/zinc-displacement-and-coordination/6496 "2023-05-26T08:22:18Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![fulvio](https://avatars.discourse-cdn.com/v4/letter/f/a88e57/32.png) [@fulvio](https://gromacs.bioexcel.eu/u/fulvio)\
**Post date:** [May 26, 2023, 8:22am UTC](https://gromacs.bioexcel.eu/t/zinc-displacement-and-coordination/6496/1 "2023-05-26T08:22:18Z")

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GROMACS version: 2023.1  
GROMACS modification: Yes/No

Dear users,  
I have to deal with a simulation of a protein containing two zinc ions, tetrahedrally coordinated but with two different sets of ligands. In the first case, one zinc is bound by four cysteines residues - and I guess all of them should be in anioni form - whereas in the second case, one zinc is coordinated by two cysteines and two histidines. I tried different Force Fields, but, actually, any attempts to perform simulation was unsuccessful, as the two zinc are displaced during NVT equilibration.  
I realized - but I am not completely sure - that the first problem could be due the fact that topology build up renders only cysteines as -CH2-SH and not S- (minus, as anion).  
Do you have any experience or any hints about the solution of this problem?  
thanks in advance

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<div class="post-metadata">

**Author:** ![fulvio](https://avatars.discourse-cdn.com/v4/letter/f/a88e57/32.png) [@fulvio](https://gromacs.bioexcel.eu/u/fulvio)\
**Post date:** [May 26, 2023, 8:16pm UTC](https://gromacs.bioexcel.eu/t/zinc-displacement-and-coordination/6496/2 "2023-05-26T20:16:34Z")

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I was wondering if someone does use H++ server, as, I guess, It May address the aforementioned issue about cysteines state  
Best