Path B - Module 44: AMBER TLeap Integration#

To accurately simulate the breaking of plastic bonds, you need a high-quality Force Field. We will use ff14SB for the PETase enzyme and the GAFF (General AMBER Force Field) for the plastic substrate.

In this module, you will learn to use MolSysMT to orchestrate the AMBER TLeap engine and generate production-ready topology and coordinate files.

import molsysmt as msm
from molsysmt import systems

# Load our complex
petase = msm.convert('pdb:6EQE', to_form='molsysmt.MolSys', selection='molecule_type=="protein"')
bhet = msm.convert('C1=CC(=CC=C1C(=O)OCCO)C(=O)OCCO', from_form='string:smiles', to_form='molsysmt.MolSys')
molsys = msm.merge([petase, bhet])

1. Parametrizing the Complex#

The function prmtop_and_inpcrd() in the thirds.tleap module automates the generation of AMBER files. It handles the naming mapping between MolSysMT and AMBER conventions.

# Generate AMBER files
# Force field: ff14SB for protein, GAFF for small molecule
try:
    prmtop, inpcrd = msm.thirds.tleap.prmtop_and_inpcrd(molsys, forcefield='ff14SB', 
                                                      small_molecule_forcefield='GAFF')
    print(f"Success! AMBER Topology generated: {msm.get_form(prmtop)}")
except Exception as e:
    print(f"TLeap parametrization failed: {e}")

2. Identifying the AMBER Form#

Once the conversion is done, the resulting objects are in file:prmtop and file:inpcrd forms. Both are explicitly classified as experimental Tier 3 forms, so production workflows require focused validation of the operations they use.

if 'prmtop' in locals():
    # Audit the prmtop
    print(f"Atoms in prmtop: {msm.get(prmtop, element='system', n_atoms=True)}")
    print(f"Has bond information? {msm.has_attribute(prmtop, 'bonded_atom_pairs')}")

🏆 Path B Challenge: The Parametrization Master#

  1. Take your Mutant PETase with the His-tag from Module 26.

  2. Try to parametrize it using the newer ff19SB force field.

  3. Check if TLeap reports any “Fatal Errors” (usually due to missing atoms you forgot to repair in Module 22).

  4. Save the generated prmtop and inpcrd paths for use in the final project.

Your industrial enzyme is now physically defined. In Module 45, we will enter the reactor and run our simulation using OpenMM Integration.