Difference between revisions of "2014 AMBER tutorial with HIV Protease"
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Revision as of 13:38, 26 March 2014
For additional Rizzo Lab tutorials see AMBER Tutorials.
In this tutorial, we will learn how to run a molecular dynamics simulation of a protein-ligand complex. We will then post-process that simulation by calculating structural fluctuations (with RMSD) and free energies of binding (MM-GBSA).
Contents
I. Introduction
II. Structural Preparation
Preparation in Chimera
Downloading the PDB file
Preparing the ligand and receptor in Chimera
Generating the final files
antechamber
parmchk
tleaP
Visualization in VMD
III. Simulation using sander
Minimization
Equilibration
Production
Running jobs on the queue
IV. Simulation Analysis
Ptraj
RMSD Plots
Measuring h-bond distances
MM-GBSA Energy Calculation
MM/GBSA is the acronym for Molecular Mechanics/Generalized Born Surface Area. This part of AMBER combines molecular mechanics (MM) with both the electrostatic (PB) and nonpolar (SA) contribution to solvation . Topology files are needed for the receptor, ligand, and receptor-ligand complex. The trajectory files generate the coordinates. Therefore, molecular dynamics is used to generate a set of snapshots taken at fixed intervals from the trajectories. These snapshots are processed to remove solvent and generate the free energy of binding.
In the AMBER_Tutorial directory, create a new directory:
mkdir 005.MMGBSA
In this new directory, create the file gb.rescore.in containing:
Single point GB energy calc &cntrl ntf = 1, ntb = 0, ntc = 2, idecomp= 0, igb = 5, saltcon= 0.00, gbsa = 2, surften= 1.0, offset = 0.09, extdiel= 78.5, cut = 99999.0, nsnb = 99999, imin = 5, maxcyc = 1, ncyc = 0, /
Then create a csh script, run.sander.rescore.csh, that contains the following lines of command:
#! /bin/csh
#PBS -l nodes=1:ppn=2
#PBS -l walltime=24:00:00
#PBS -o zzz.qsub.out
#PBS -e zzz.qsub.err
#PBS -V
set workdir = "/nfs/user03/yechen1/AMBER-Tutorial/005.MMGBSA"
set sander = "/nfs/user03/wjallen/local/amber12/bin/sander"
cd ${workdir}
$sander -O -i gb.rescore.in -o gb.rescore.out.com -p ../002.ANTE.TLEAP /1LOQ.com.gas.leap.prm7 \
-c ../002.ANTE.TLEAP/1LOQ.com.gas.leap.rst7 -y ../004.PTRAJ/1LOQ.com.trj.stripfit \
-r restrt.com -ref ../002.ANTE.TLEAP/1LOQ.com.gas.leap.rst7 -x mdcrd.com -inf mdinfo.com
$sander -O -i gb.rescore.in -o gb.rescore.out.lig -p ../002.ANTE.TLEAP/1LOQ.lig.gas.leap.prm7 \
-c ../002.ANTE.TLEAP/1LOQ.lig.gas.leap.rst7 -y ../004.PTRAJ/1LOQ.lig.trj.stripfit \
-r restrt.lig -ref ../002.ANTE.TLEAP/1LOQ.lig.gas.leap.rst7 -x mdcrd.lig -inf mdinfo.lig
$sander -O -i gb.rescore.in -o gb.rescore.out.rec -p ../002.ANTE.TLEAP/1LOQ.rec.gas.leap.prm7 \
-c ../002.ANTE.TLEAP/1LOQ.rec.gas.leap.rst7 -y ../004.PTRAJ/1LOQ.rec.trj.stripfit \
-r restrt.rec -ref ../002.ANTE.TLEAP/1LOQ.rec.gas.leap.rst7 -x mdcrd.rec -inf mdinfo.rec
exit
~ ~ ~ ~
Then this script should be sent to the queue, i.e., qsub the script using the commands:
qsub run.sander.rescore.csh
You can monitor your progress by typing
qstat -u username
When the job is complete, you will obtain the following output files: gb.rescore.out.com, gb.rescore.out.lig, and gb.rescore.out.rec In these files, the single point energy calculation results will be written for each individual frame. It will be found in the results section and the output file will have an infrastrucutre that is similar to the following:
FINAL RESULTS
NSTEP ENERGY RMS GMAX NAME NUMBER
1 3.6269E+03 1.8737E+01 1.0472E+02 CB 585
BOND = 580.2786 ANGLE = 1563.7704 DIHED = 2161.5659
VDWAALS = -1684.2762 EEL = -13809.8494 EGB = -2953.6681
1-4 VDW = 756.7767 1-4 EEL = 7260.2823 RESTRAINT = 0.0000
ESURF = 9752.0291
minimization completed, ENE= 0.36269092E+04 RMS= 0.187371E+02
TRAJENE: Trajectory file ended
TRAJENE: Trajene complete.
In the command line, type:
grep VDWAALS gb.rescore.out.com > vdw.com.txt. grep ESURF gb.rescore.out.com > surf.com.txt.
You can take these text files, import them into Excel, and do the rest of your modifications there.
Equations for analysis
Remember that to obtain the Gvdw term, you need to take the SASA (which is ESURF) and input into equation 1:
ΔGnonpolar = SASA*0.00542 + 0.92
Also, the mmgbsa of a given system can be determined by equation 2:
ΔGmmgbsa = ΔGvdw + ΔGcoul + ΔGpolar + ΔGnonpolar
From the output file:
VDWAALS = ΔGvdw
EELS = ΔGcoul
EGB = ΔGpolar
You can then easily calculate the ΔΔGbind by using equation 3:
ΔΔGbind = ΔGmmgbsa,complex – (ΔGmmgbsa,lig + ΔGmmgbsa,rec) You will want to careful when doing your analysis that the results from frame 1 for the receptor and ligand are subtracted from the results from frame 1 for your complex. By doing this in excel, you should have 2000 frames for each, and the values should cleanly line up. Finally, you will want to plot your ΔΔGbind and examine if you see corresponding changes in the ligand position and the ΔΔGbind. Also, you should determine the mean and standard deviation for your ΔΔGbind.
Plotting Energy
When your rescoring calculation finishes, you have the following three output files: "gb.rescore.out.com", "gb.rescore.out.lig", and "gb.rescore.out.rec".
Use the following script, entitled get.mmgbsa.bash, to extract data and calculate MMGBSA energy for each snap shot.
#! /bin/bash
# by Haoquan
echo com lig rec > namelist
LIST=`cat namelist`
for i in $LIST ; do
grep VDWAALS gb.rescore.out.$i | awk '{print $3}' > $i.vdw
grep EGB gb.rescore.out.$i | awk '{print $9}' > $i.polar
grep EELS gb.rescore.out.$i | awk '{print $6}' > $i.coul
grep ESURF gb.rescore.out.$i | awk '{print $3 * 0.00542 + 0.92}' > $i.surf
paste -d " " $i.vdw $i.polar $i.surf $i.coul | awk '{print $1 + $2 + $3 + $4}' > data.$i
rm $i.*
done
paste -d " " data.com data.lig data.rec | awk '{print $1 - $2 - $3}' > data.all
for ((j=1; j<=`wc -l data.all | awk '{print $1}'`; j+=1)) do
echo $j , >> time
done
paste -d " " time data.all > MMGBSA_vs_time.dat
rm namelist time data.*
To run this script do:
bash get.mmgbsa.sh
This will create a text file called MMGBSA_vs_time.dat with x and y values separated by a space and comma. These values can be imported to Excel or Origin or to XMGRACE if you are using Linux:
xmgrace MMGBSA_vs_time.dat
2013 AMBER MMGBSA plot.jpg
