# Hydrogens in ligand are added in wrong positions by cns

**URL:** <https://ask.bioexcel.eu/t/hydrogens-in-ligand-are-added-in-wrong-positions-by-cns/687>\
**Category:** HADDOCK\
**Created:** [December 18, 2017, 4:03pm UTC](https://ask.bioexcel.eu/t/hydrogens-in-ligand-are-added-in-wrong-positions-by-cns/687 "2017-12-18T16:03:29Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![vlachj](https://avatars.discourse-cdn.com/v4/letter/v/848f3c/32.png) [@vlachj](https://ask.bioexcel.eu/u/vlachj)\
**Post date:** [December 18, 2017, 4:03pm UTC](https://ask.bioexcel.eu/t/hydrogens-in-ligand-are-added-in-wrong-positions-by-cns/687/1 "2017-12-18T16:03:29Z")

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Hi,  
I have been trying to dock an inositol trisphosphate ligand on a protein but hydrogens in the ligand molecule get misplaced at the initial stage of calculation. When cns removes and then re-adds hydrogens during psf file generation, two ring hydrogens are placed in an impossible position while the rest of the ring hydrogens have somewhat odd positions. You can get the pdb [here](https://drive.google.com/file/d/1gJyFg72wAz5okci9fDd8SyteWqf8ur9m/view?usp=sharing).

I built the molecule in Avogadro and obtained the topology and parameters files from acpype. The atom types and charges in the top file seem to be correct, and changing the ring hydrogens type from h1\_ to hc\_ did not help.

Docking inositol hexakisphosphate that was prepared in the same way worked fine.

I’m not sure what to troubleshoot or focus on next and I would appreciate a lot any comment or advice.

Thanks,  
Jiri

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**Author:** ![amjjbonvin](https://dub1.discourse-cdn.com/flex013/user_avatar/ask.bioexcel.eu/amjjbonvin/32/23_2.png) [@amjjbonvin](https://ask.bioexcel.eu/u/amjjbonvin)\
**Post date:** [December 18, 2017, 4:18pm UTC](https://ask.bioexcel.eu/t/hydrogens-in-ligand-are-added-in-wrong-positions-by-cns/687/2 "2017-12-18T16:18:30Z")

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It looks like the topology does not uniquely define the hydrogen positions. By default all hydrogens are rebuild. You can change that by editing in the protocol directory `generate_X.inp` where X corresponds to your ligand (e.g. B if second molecule. Change then the following lines:

```auto
{* which hydrogens to build *}
{+ choice: "all" "unknown" +}
{===>} hydrogen_build="unknown";

```

(Assuming here you are running a local version of HADDOCK)

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**Author:** ![vlachj](https://avatars.discourse-cdn.com/v4/letter/v/848f3c/32.png) [@vlachj](https://ask.bioexcel.eu/u/vlachj)\
**Post date:** [December 18, 2017, 4:59pm UTC](https://ask.bioexcel.eu/t/hydrogens-in-ligand-are-added-in-wrong-positions-by-cns/687/3 "2017-12-18T16:59:52Z")

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That did the trick.  
Thanks a lot!