# Unambigous restraints with specific atoms

**URL:** https://ask.bioexcel.eu/t/unambigous-restraints-with-specific-atoms/1940
**Category:** Uncategorized
**Created:** [April 21, 2020, 9:11am UTC](https://ask.bioexcel.eu/t/unambigous-restraints-with-specific-atoms/1940 "2020-04-21T09:11:24Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![Leo](https://avatars.discourse-cdn.com/v4/letter/l/c2a13f/32.png) [@Leo](https://ask.bioexcel.eu/u/Leo)
#### Post date: [April 21, 2020, 9:11am UTC](https://ask.bioexcel.eu/t/unambigous-restraints-with-specific-atoms/1940/1 "2020-04-21T09:11:24Z")

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What is the CNS format for writing unambigous restraints with specific atoms instead of just the entire residues. For example I want to set the upper distance limit for the alpha carbon of residue 229 to 4Å. How would I do that?

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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: [April 21, 2020, 12:06pm UTC](https://ask.bioexcel.eu/t/unambigous-restraints-with-specific-atoms/1940/2 "2020-04-21T12:06:55Z")

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Described in our original Nature Protocol 2010 paper.

One example here:

`assign (resid 10 and name CA and segid A) (resid 20 and name CA and segid B) 4.0 4.0 0.0`

And also described for example in the following online tutorial:

```
https://www.bonvinlab.org/education/HADDOCK24/HADDOCK24-Xlinks/#scenarios-for-docking---how-to-make-use-of-ms-data-in-haddock
```