# Haddock semi-flexibility?

**URL:** <https://ask.bioexcel.eu/t/haddock-semi-flexibility/5872>\
**Category:** HADDOCK\
**Created:** [August 31, 2025, 5:15am UTC](https://ask.bioexcel.eu/t/haddock-semi-flexibility/5872 "2025-08-31T05:15:18Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Eugeneng991031](https://avatars.discourse-cdn.com/v4/letter/e/8dc957/32.png) [@Eugeneng991031](https://ask.bioexcel.eu/u/Eugeneng991031)\
**Post date:** [August 31, 2025, 5:15am UTC](https://ask.bioexcel.eu/t/haddock-semi-flexibility/5872/1 "2025-08-31T05:15:18Z")

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Hi, good day to everyone , if for example, from literature, I know my protein-protein interaction is rigid body interaction, in HADDOCK, during the “input parameter”, is it right if i set the semi-flexible region as rigid?

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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:** [August 31, 2025, 5:48pm UTC](https://ask.bioexcel.eu/t/haddock-semi-flexibility/5872/2 "2025-08-31T17:48:15Z")

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There is nothing like a rigid-body interaction.

When in the field we speak of rigid-body interaction we mean there are no conformational changes large than 1A backbone RMSD.  
There will always be a bit of small conformational changes. For sure of the side-chains.

So better to leave the flexibility options to their default 🙂

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<div class="post-metadata">

**Author:** ![Eugeneng991031](https://avatars.discourse-cdn.com/v4/letter/e/8dc957/32.png) [@Eugeneng991031](https://ask.bioexcel.eu/u/Eugeneng991031)\
**Post date:** [September 1, 2025, 12:45pm UTC](https://ask.bioexcel.eu/t/haddock-semi-flexibility/5872/3 "2025-09-01T12:45:39Z")

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Noted with thanks!! Much appreciated!