Parameterization of an adenylylated tyrosine residue in CHARMM36

GROMACS version: 2022.4
GROMACS modification: No

I am trying to implement an adenylylated (AMPylated) tyrosine residue as additional entry in “aminoacids.rtp” of the charmm36-jul2022 forcefield. I obtained a stream-file (.str) from CGenFF for the modified residue, which I converted to .itp and .prm using “cgenff_charmm2gmx.py”. After creating the corresponding .rtp entry for my modified residue, I can run pdb2gmx without problems but grompp gives errors related to “No default Bond types”, “No default U-B types” and “No default Proper Dih. types”, which does not get resolved with adding the parameter file inclusion statement “#include yam.prm” to topol.top. I am not sure if this is related to the atom types I am using, since I did not rename the CGenFF atom types in my rtp file entry? Although all the atom types I am using are listed in “atomtypes.atp”, I am not sure if there is a full set of parameters for all CGenFF atom types in my rtp file entry?

Here would be my rtp file entry for the modified (i.e. AMPylated) tyrosine residue:

[ YAM ]
; 
  [ atoms ]
        N      NH1     -0.4700   1
      H07        H      0.3100   1
       CA      CT1      0.0700   1
      H08      HB1      0.0900   1
       CB      CT2     -0.1800   2
       CG      CA       0.0000   3
      CD1      CA      -0.1150   4
      CD2      CA      -0.1150   4
      CE1      CA      -0.1150   5
      CE2      CA      -0.1150   5
       CZ      CA       0.1100   6
       OH      OH1     -0.2380   6
       P       PG1      1.4030   7
      O2P      OG2P1   -0.7210   7
      O3P      OG2P1   -0.7210   7
      C5'      CG321   -0.0730   8
      O5'      OG303   -0.5820   8
      C4'      CG3C51   0.1310   9
      O4'      OG3C51  -0.4620   9
      C3'      CG3C51   0.1420  10
      O3'      OG311   -0.6470  10
      C2'      CG3C51   0.1410  11
      O2'      OG311   -0.6480  11
      C1'      CG3C51   0.1440  12
       N1      NG2R62  -0.7410  13
       C2      CG2R64   0.4950  14
       N3      NG2R62  -0.7510  15
       C4      CG2RC0   0.4260  16
       C5      CG2RC0   0.2800  17
       C6      CG2R64   0.4630  18
       N6      NG2S3   -0.7640  19
       N7      NG2R50  -0.7180  20
       C8      CG2R53   0.3390  21
       N9      NG2R51  -0.0560  22
      H09      HGR62    0.1280  23
      H02      HGR52    0.1410  24
     H012      HGR61    0.1150  25
     H014      HGR61    0.1150  26
      H05      HGR61    0.1150  27
      H06      HGR61    0.1150  28
      H11      HGA2     0.0900  30
      H12      HGA2     0.0900  31
      H14      HGA2     0.0900  32
      H15      HGA2     0.0900  33
      H16      HGA1     0.0900  34
      H17      HGA1     0.0900  35
      H18      HGP1     0.4200  36
      H19      HGA1     0.0900  37
      H20      HGP1     0.4200  38
      H21      HGA1     0.0900  39
      H22      HGP4     0.3770  40
      H23      HGP4     0.3770  41
        C        C      0.5100  42
        O        O     -0.5100  42
  [ bonds ]
        N     CA
        N     H07
       CA      C
       CA     CB
       CA    H08
        C      O
       CB     CG
       CB    H11
       CB    H12
       CG    CD1
       CG    CD2
      CD1    CE1
      CD1    H014
      CD2    CE2
      CD2    H06
      CE1    CZ
      CE1    H012
      CE2    CZ
      CE2    H05
       CZ     OH
       OH      P
        P    O2P
        P    O3P
        P    O5'
      C5'    O5'
      C5'    C4'
      C5'    H14
      C5'    H15
      C4'    O4'
      C4'    C3'
      C4'    H16
      O4'    C1'
      C3'    O3'
      C3'    C2'
      C3'    H17
      O3'    H18
      C2'    O2'
      C2'    C1'
      C2'    H19
      O2'    H20
      C1'    H21
       N1     C2
       N1     C6
       C2     N3
       C2    H09
       N3     C4
       C4     C5
       C5     C6
       C5     C8
       C6     N6
       N6    H22
       N6    H23
       N7    C5
       N7    C8
       N9    C1'
       N9    C8
       N9    C4
  [ impropers ]
        N    -C    CA   H07
        C    CA    +N     O
  [ cmap ]
       -C     N    CA     C    +N

I would be very happy for any help to resolve this issue.

Many thanks
Michael