2023 AMBER tutorial 2 with PDBID 3WZE
Contents
Introduction
Directory Setup
As always, we set up folders to keep us organized as we move generate files:
mkdir 001_structure mkdir 002_parameters mkdir 003_leap mkdir 004_equil mkdir 005_production
3WZE Structures
Receptor
Ligand
Amber Simulation Parameters
To generate parameters for the simulation, we must implement the following:
antechamber -i ../001_structure/3wze_lig_wH.mol2 -fi mol2 -o 3wze_ligand_antechamber.mol2 -fo mol2 -at gaff2 -c bcc -rn LIG -nc 0
nc = 0 because the charge on the ligand is 0. If your ligand is non-zero, enter the appropriate charge at the end of this line. It may be helpful to check the protonation state of the ligand at pH 7. Once 3wze_ligand_antechamber.mol2 output file is generated, run parmch2:
parmchk2 -i 3wze_ligand_antechamber.mol2 -f mol2 -o 3wze_ligand.am1bcc.frcmod
TLEaP
Next we will generate the AMBER topology file and coordinate files. Switch to the directory:
vi leap.in
Two types of files will be generated, parm7 (topology) and rst7 (coordinates). Create the input file:
vi leap.in
And then input the following (make sure you change the username):
#!/USERNAME/bin/sh
###load protein force field
source leaprc.protein.ff14SB
###load GAFF force field (for our ligand)
source leaprc.gaff
###load TIP3P (water) force field
source leaprc.water.tip3p
###load ions frcmod for the tip3p model
loadamberparams frcmod.ionsjc_tip3p
###needed so we can use igb=8 model
set default PBradii mbondi3
###load protein pdb file
rec=loadpdb ../000_structure/3wze_rec.pdb
##@make disulfide bond
###load ligand frcmod/mol2
loadamberparams ../000_structure/3wze_ligand.am1bcc.frcmod
lig=loadmol2 ../000_structure/3wze_ligand_antechamber.mol2
###create gase-phase complex
gascomplex= combine {rec lig}
###write gas-phase pdb
savepdb gascomplex 3wze.gas.complex.pdb
###write gas-phase toplogy and coord files for MMGBSA calc
saveamberparm gascomplex 3wze.complex.parm7 3wze.gas.complex.rst7
saveamberparm rec 3wze.gas.receptor.parm7 3wze.gas.receptor.rst7
saveamberparm lig 3wze.gas.ligand.parm7 3wze.gas.ligand.rst7
###create solvated complex (albeit redundant)
solvcomplex= combine {rec lig}
###solvate the system
solvateoct solvcomplex TIP3PBOX 12.0
###Neutralize system
addions solvcomplex Cl- 0
addions solvcomplex Na+ 0
#write solvated pdb file
savepdb solvcomplex 3wze.wet.complex.pdb
###check the system
charge solvcomplex
check solvcomplex
###write solvated toplogy and coordinate file
saveamberparm solvcomplex 3wze.wet.complex.parm7 3wze.wet.complex.rst7
quit
Once the files are generated, transfer the parm7 and rst7 files to the local environment. You can run them in Chimera to check the build. Open the protein, then open TOOLS--MD/ENSEMBLE ANALYSIS--MD MOVIE. Open the parm7 in prmtop box and then add the rst7 as a trajectory. Then click OK.
Equilibration
Next, we will minimize and equilibrate the system over nine successive steps. For information about the different parameters see the AMBER16 manual.
Change directory to:
cd 004_equil
The first step is to create the new file:
vi 01.min.md
And insert the following: Minimize all the hydrogens
&cntrl imin=1, ! Minimize the initial structure ntmin=2, ! Use steepest descent Ryota Added maxcyc=5000, ! Maximum number of cycles for minimization ntb=1, ! Constant volume ntp=0, ! No pressure scaling ntf=1, ! Complete force evaluation ntwx= 1000, ! Write to trajectory file every ntwx steps ntpr= 1000, ! Print to mdout every ntpr steps ntwr= 1000, ! Write a restart file every ntwr steps cut= 8.0, ! Nonbonded cutoff in Angstroms ntr=1, ! Turn on restraints restraintmask="!@H=", ! atoms to be restrained restraint_wt=5.0, ! force constant for restraint ntxo=1, ! Write coordinate file in ASCII format ioutfm=0, ! Write trajectory file in ASCII format /
You'll want to pay close attention to the restraint mask - it lifts in later steps.
