# User-specified modified amino acids

**URL:** <https://ask.bioexcel.eu/t/user-specified-modified-amino-acids/4109>\
**Category:** HADDOCK\
**Created:** [February 11, 2023, 5:03pm UTC](https://ask.bioexcel.eu/t/user-specified-modified-amino-acids/4109 "2023-02-11T17:03:38Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![gabriong](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@gabriong](https://ask.bioexcel.eu/u/gabriong)\
**Post date:** [February 11, 2023, 5:03pm UTC](https://ask.bioexcel.eu/t/user-specified-modified-amino-acids/4109/1 "2023-02-11T17:03:38Z")

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Is it possible for users to specify their own modified amino acids (outside the list supported by HADDOCK) and have them treated like a ligand (but still remain attached to rest of the protein) during docking?

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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:** [February 13, 2023, 7:01pm UTC](https://ask.bioexcel.eu/t/user-specified-modified-amino-acids/4109/2 "2023-02-13T19:01:48Z")

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This is not possible - at best you could defined those as HETATM but they will not be connected to the adjacent amino acids (you could impose a few distance restraints to keep them in place…)