Adding non-natural amino acid

GROMACS version: 2020.5
GROMACS modification: Yes

Hi,

I am trying to run MD simulation for a protein-peptide complex having two sulfotyrosine residues using AMBER99sb-ILDN force field. I followed the gromacs tutorial “Adding a Residue to a Force Field” , and edited the .rtp and .hbd files and successfully generated the .gro and .itp and .top files for complex. But while adding ions, it is showing following error:
**~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~**
GROMACS: gmx grompp, version 2020.5
Executable: /usr/local/gromacs/bin/gmx_mpi
Data prefix: /usr/local/gromacs
Working dir: /media/kmlab/e0a76a38-d3f0-409e-8cf5-7d35c284604d/Nupur/sulfopeptide_Tyr3739
Command line:
** gmx_mpi grompp -f ions.mdp -c cxc3_B_em_solv.gro -p topol.top -o ions.tpr**
Ignoring obsolete mdp entry 'ns_type’
NOTE 1 [file ions.mdp]:
** With Verlet lists the optimal nstlist is >= 10, with GPUs >= 20. Note**
** that with the Verlet scheme, nstlist has no effect on the accuracy of**
** your simulation.**

Setting the LD random seed to -75558916
Generated 2145 of the 2145 non-bonded parameter combinations
Generating 1-4 interactions: fudge = 0.5
Generated 2145 of the 2145 1-4 parameter combinations

ERROR 1 [file topol_Protein_chain_B.itp, line 333]:
** No default Bond types**

ERROR 2 [file topol_Protein_chain_B.itp, line 334]:
** No default Bond types**

ERROR 3 [file topol_Protein_chain_B.itp, line 335]:
** No default Bond types**

ERROR 4 [file topol_Protein_chain_B.itp, line 336]:
** No default Bond types**

ERROR 5 [file topol_Protein_chain_B.itp, line 370]:
** No default Bond types**

ERROR 6 [file topol_Protein_chain_B.itp, line 371]:
** No default Bond types**

ERROR 7 [file topol_Protein_chain_B.itp, line 372]:
** No default Bond types**

ERROR 8 [file topol_Protein_chain_B.itp, line 373]:
** No default Bond types**

ERROR 9 [file topol_Protein_chain_B.itp, line 1115]:
** No default Angle types**

ERROR 10 [file topol_Protein_chain_B.itp, line 1117]:
** No default Angle types**

ERROR 11 [file topol_Protein_chain_B.itp, line 1118]:
** No default Angle types**

ERROR 12 [file topol_Protein_chain_B.itp, line 1119]:
** No default Angle types**

ERROR 13 [file topol_Protein_chain_B.itp, line 1120]:
** No default Angle types**

ERROR 14 [file topol_Protein_chain_B.itp, line 1121]:
** No default Angle types**

ERROR 15 [file topol_Protein_chain_B.itp, line 1122]:
** No default Angle types**

ERROR 16 [file topol_Protein_chain_B.itp, line 1123]:
** No default Angle types**

ERROR 17 [file topol_Protein_chain_B.itp, line 1124]:
** No default Angle types**

ERROR 18 [file topol_Protein_chain_B.itp, line 1179]:
** No default Angle types**

ERROR 19 [file topol_Protein_chain_B.itp, line 1181]:
** No default Angle types**

ERROR 20 [file topol_Protein_chain_B.itp, line 1182]:
** No default Angle types**

ERROR 21 [file topol_Protein_chain_B.itp, line 1183]:
** No default Angle types**

ERROR 22 [file topol_Protein_chain_B.itp, line 1184]:
** No default Angle types**

ERROR 23 [file topol_Protein_chain_B.itp, line 1185]:
** No default Angle types**

ERROR 24 [file topol_Protein_chain_B.itp, line 1186]:
** No default Angle types**

ERROR 25 [file topol_Protein_chain_B.itp, line 1187]:
** No default Angle types**

ERROR 26 [file topol_Protein_chain_B.itp, line 1188]:
** No default Angle types**

ERROR 27 [file topol_Protein_chain_B.itp, line 1568]:
** No default Proper Dih. types**

ERROR 28 [file topol_Protein_chain_B.itp, line 1569]:
** No default Proper Dih. types**

ERROR 29 [file topol_Protein_chain_B.itp, line 1570]:
** No default Proper Dih. types**

ERROR 30 [file topol_Protein_chain_B.itp, line 1674]:
** No default Proper Dih. types**

ERROR 31 [file topol_Protein_chain_B.itp, line 1675]:
** No default Proper Dih. types**

ERROR 32 [file topol_Protein_chain_B.itp, line 1676]:
** No default Proper Dih. types**

ERROR 33 [file topol_Protein_chain_B.itp, line 1899]:
** No default Improper Dih. types**

ERROR 34 [file topol_Protein_chain_B.itp, line 1901]:
** No default Improper Dih. types**

ERROR 35 [file topol_Protein_chain_B.itp, line 1911]:
** No default Improper Dih. types**

ERROR 36 [file topol_Protein_chain_B.itp, line 1913]:
** No default Improper Dih. types**

Excluding 3 bonded neighbours molecule type 'Protein_chain_A’
Excluding 3 bonded neighbours molecule type 'Protein_chain_B’
Excluding 2 bonded neighbours molecule type 'SOL’

NOTE 2 [file topol.top, line 48]:
** System has non-zero total charge: -1.000000**
** Total charge should normally be an integer. See**
** http://www.gromacs.org/Documentation/Floating_Point_Arithmetic**
** for discussion on how close it should be to an integer.**


There were 2 notes
-------------------------------------------------------
Program: gmx grompp, version 2020.5
Source file: src/gromacs/gmxpreprocess/grompp.cpp (line 1928)

Fatal error:
There were 36 errors in input file(s)

For more information and tips for troubleshooting, please check the GROMACS
website at Errors - Gromacs
-------------------------------------------------------
application called MPI_Abort(MPI_COMM_WORLD, 1) - process 0
[unset]: write_line error; fd=-1 buf=:cmd=abort exitcode=1
:
system msg for write_line failure : Bad file descriptor
**~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~**
I checked the atoms for which ‘no default bonds types/ angles/ improper diherals’ were mentioned and it mainly involves the sulfotyrosine. I tried editing the ffbonded.itp file but could not understand how to do it. Kindly help me with this.

Hi,

As far as I understood from your comment, the missing interactions (bond, angle and dihedral) are involving the sulfur atom and you want to add the parameter for those parameter in the ffbonded.itp.
If you know the parameters for the missing interactions (and they are compatible with amber AMBER99sb-ILDN, then you can add them to the ffbonded.itp. Here you can find information on the structure of ffbonded.itp file Parameter files — GROMACS 2021 documentation.
The interactions are defined by atoms type and funct type. Definition of the function type can be find in table 14 Parameter files — GROMACS 2021 documentation
I hope it helps
Best regards
Alessandra

Hello
Thanks for the help. I generated the parameter file using Amber tools for sulfotyrosine and added the parameters to ffbonded.itp as you suggested.

Regards
Nupur Nagar