# Parametrization of pyroglutamate

**URL:** <https://gromacs.bioexcel.eu/t/parametrization-of-pyroglutamate/13606>\
**Category:** User discussions\
**Tags:** forcefield, simulation-setup\
**Created:** [July 18, 2026, 2:11pm UTC](https://gromacs.bioexcel.eu/t/parametrization-of-pyroglutamate/13606 "2026-07-18T14:11:22Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![mostafagh98](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mostafagh98/32/4214_2.png) [@mostafagh98](https://gromacs.bioexcel.eu/u/mostafagh98)\
**Post date:** [July 18, 2026, 2:11pm UTC](https://gromacs.bioexcel.eu/t/parametrization-of-pyroglutamate/13606/1 "2026-07-18T14:11:22Z")

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GROMACS version: 2026  
GROMACS modification: No

Hi everyone,

I am currently setting up simulations of Aβ(pE3-42) using the CHARMM36m force field in GROMACS.

The N-terminal residue of this peptide is pyroglutamate (pGlu/PCA). Because this is a cyclized residue lacking a free N-terminal charge, it is not included in the standard CHARMM36m force field.

Could anyone advise on the best approach to parametrize and integrate pyroglutamate into CHARMM36m for use with GROMACS?

Any guidance, relevant literature, or suggestions would be greatly appreciated.

Thanks in advance for your help!

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**Author:** ![slovas](https://avatars.discourse-cdn.com/v4/letter/s/e274bd/32.png) [@slovas](https://gromacs.bioexcel.eu/u/slovas)\
**Post date:** [July 20, 2026, 3:50pm UTC](https://gromacs.bioexcel.eu/t/parametrization-of-pyroglutamate/13606/2 "2026-07-20T15:50:08Z")

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The latest Tinker distribution has charmm36m parameters for pGlu, convert it over to gromacs format

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<div class="post-metadata">

**Author:** ![mostafagh98](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mostafagh98/32/4214_2.png) [@mostafagh98](https://gromacs.bioexcel.eu/u/mostafagh98)\
**Post date:** [July 28, 2026, 5:29pm UTC](https://gromacs.bioexcel.eu/t/parametrization-of-pyroglutamate/13606/3 "2026-07-28T17:29:06Z")

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Thanks a lot for your response.