Revision as of 18:52, 1 April 2021

In this tutorial, we will be modeling ligand binding to our receptor using AMBER 16, a molecular dynamics simulation software package created in part by our very own Carlos Simmerling.

Initial Structures

We will be saving all of our initial structures in a directory called 01.structure.

Protein

For the initial protein structure, we will be using the PDB we downloaded from the Protein Data Bank Website (see here). Load this PDB into chimera and delete the ligand and any nonstandard residues (ex. waters). Save this as a PDB file, 1s19_fresh.pdb, and transfer it to your 01.structure folder.

Ligand

For the ligand, we will again load the 1s19 pdb file from the Protein Data Bank in Chimera. We will delete everything except for the ligand. For this example, the ligand is under the name MC9. To delete everything:

Select -> Residue -> MC9
Select -> Invert (all models)
Actions -> Atoms/Bonds -> Delete

With the ligand isolated, we will add hydrogens and charge. To do this:

Tools -> Structure Editing -> Add H
Tools -> Structure Editing -> Add Charge -> (have Amber ff14SB and AM1-BCC selected) -> Ok

Save this as a mol2 file in Chimera and save under the name 1s19_ligand_dockprep.mol2.

NOTE It is VERY important to make sure that Chimera adds hydrogens correctly. For this particular ligand the net charge was zero and Chimera was able to model the hydrogens correctly. Many times however, Chimera will add extra hydrogens. If it does, just select the extra hydrogen and go to:

Actions -> Atoms/Bonds -> Delete

Your ligand will then be protonated and charged correctly.

Generating Parameters for the Simulation

In order to utilize Amber for molecular dynamic, parameters for the bio molecules will be needed. Luckily, there have been years of parameter development so parameters for the protein do not have to worried about. However, the small ligand does not have parameters in the standard protein force field. Consequently, we will need to generate a fcmod file specific for the ligand.

Building the System with TLeap

Equilibration

Input Files

Run Script

Produduction

Input File

Run Script

Analysis

RMSD

Hydrogen Bonds

MMGBSA