2021 AMBER tutorial 1 with PDBID 1HW9
In this tutorial, we'll be exploring the wonders of molecular dynamics through the use of AMBER 16. AMBER 16 we'll help study the binding characteristics of the ligand to the target protein!
It's important to stay organized during this process as we'll be generating a number of files during the process. Overall, we'll be working within five directories. They should be created as follows:
mkdir 001_structure mkdir 002_parameters mkdir 003_leap mkdir 004_equil mkdir 005_production
Before proceeding, double-check that all directories have correctly been made.
Let's move into our directory titled 001_structure.
We need to retrieve a fresh copy of the receptor before proceeding forward. Even if you've done the DOCK tutorial, you should still retrieve a fresh .pdb just in case Chimera did something wrong during the preparation process. In order to do so, head over to the PDB website and type in 1HW9 into the header. It should take you straight to the webpage. Download the system as a pdb and open it in Chimera. Our focus will be on Chain A of the complex. In order to visualize the chain:
Select -> Chain -> A
Notice, however, that this does not remove Chains B, C, and D from our view. We need to perform this action manually.
Select -> Invert (Selected Molecules) -> Actions -> Atoms/Bonds -> Delete
After deletion, the only thing remaining should be Chain A of the original file. It is within your best interest to save this session as you'll need to come back to this file when preparing the ligand. Doing so will prevent you from having to do the above deletion step again.
File -> Save Session As ->
Now that the session has been saved, we can go ahead and isolate the receptor. While we've isolated Chain A, you'll notice that Simvastatin is still located on the molecule. In order to remove everything besides HMGR, we need to do the following:
Select -> Residue -> ADP -> Actions -> Atoms/Bonds -> Delete Select -> Residue -> HOH -> Actions -> Atoms/Bonds -> Delete Select -> Residue -> SIM -> Actions -> Atoms/Bonds -> Delete
With the receptor isolated, go ahead and save the file as
Open the session in Chimera we previously saved that consisted of Chain A with both the receptor and Simvastatin ligand. This time around, we'll be using the session file to isolate the ligand instead of the receptor.
Select -> Residue -> SIM -> Select -> Invert (Selected Molecules) -> Actions -> Atoms/Bonds -> Delete
We'll need to properly protonate the ligand in order for the AMBER calculations to function:
Tools -> Structure Editing -> Add H Tools -> Structure Editing -> Add Charge -> (have Amber ff14SB and AM1-BCC selected) -> Ok
Once done, make sure to save your file as:
NOTE: Before proceeding, make sure both the ligand and receptor file you just created have been copied from your local computer to the 001_structure directory in your Seawulf account.
Let's move into the second directory:
Here, we'll be generating force field parameters for our ligand so that AMBER can use them in later calculations. We'll be doing this using antechamber and parmchk2:
antechamber -i ../001_structure/1HW9_lig_wH.mol2 -fi mol2 -o 1HW9_ligand_antechamber.mol2 -fo mol2 -at gaff2 -c bcc -rn LIG -nc -1
Notice the -nc flag at the end of the command line. Make sure that this value corresponds to the protonation state of your ligand! Once the output file is generated, we need to run parmch2 to generate a frcmod file:
parmchk2 -i 1HW9_ligand_antechamber.mol2 -f mol2 -o 1HW9_ligand.am1bcc.frcmod