2010 AMBER Tutorial with Biotin and Streptavidin

What is AMBER?

Amber - Assisted Model Building with Energy Refinement - is a suite of about 50 programs that can be used to simulate, study and analyze macromolecular systems such as proteins dissolved in water at physiological conditions. Amber10, the current version (Amber11 soon to be released) of Amber, is extremely advanced, powerful and fast. PMEMD, particle mesh Ewald MD (boundary condition treatment / parallelized code) can churn out 314 ps/day of data for the system dihydrofolate reductase (159 residue protein) in TIP3P water (23,558 total atoms). However, because PMEMD lacks the ability to restrain the atoms we need properly, we will be using SANDER to perform most of our simulations.

Quick Tips

The Amber 10 Manual is the primary resource when trying to learn what variables and keywords mean and what they do. Using Adobe Acrobat to view the file, you can simply search the document for keywords, which saves much time.

There is a mailing list you could sign-up for, as an additional resource.

Using and editing this wiki:

Files, Programs, Scripts, etc.

Filename.extension

Contents of Filename.extension

• Explanation
• content -> description

If more contents of Filename.extension

• Explanation
• content -> description

Generating Data

...

ptraj - Analyzing Your Data

ptraj is an analysis program included in the AMBER suite (AMBERtools) designed in part by Dr. Thomas Cheatham. See this website.

A useful and recommended program - merely a text file with functional syntax - to write is:

RUNTRAJ

#!/bin/csh
ptraj parameter_aka_topology_filename.parm ptraj_input_filename.1.in > ouput_results_ptraj.1.out
exit

(When writing the above, one depressed 'Enter' on the keyboard, which is 'recorded' by vim. So, when the file is executed, it would be like hitting 'Enter' if you were entering the commands by hand in the shell. The names of the files - "parameter_aka_topology_filename.parm", "ptraj_input_filename.1.in" and "output_results_ptraj.1.out" were names I chose to illustrate the importance of neglecting brevity to be as clear as possible when naming files. It is also useful to use numbers to start a file's name.)

#!/bin/csh -> will be in nearly all of the programs you will write - unless you dabble in Cpp or G77. It tells the shell to treat the contents of this here file as if the contents were being typed in the shell by hand.

ptraj -> has been aliased in your .cshrc file and will initialize ptraj once read by the machine.

parameter_aka_topology_filename.parm -> is the .parm file you would like to specify.

ptraj_input_filename.1.in -> is the set of instruction you want ptraj to read and perform, in an input file (This would be "ptraj.concatenate.strip.trj" in the coming examples).

exit -> will exit from ptraj when the ptraj_input_filename.1.in has completed its instruction(s).

Executing it:

Herbie:~> csh RUNTRAJ

Some Sample Skripts

This page contains a brief list of ptraj functions and their syntax. The commands in "Some Sample Skripts" can be combined with most combinations of other functions to suit the need.

Combine Production Trajectories while Stripping the Water Molecules

ptraj.1.in

 trajin ../003.SANDER/10md.trj 1 1000 1

• trajin -> tells ptraj to "read-in" the file which comes after it
• ../003.SANDER/10md.trj -> is the file to be "read-in"
• 1 1000 1 -> tells ptraj to use the first to the 1000th snapshot of the trajectory. The third number, "1", is telling ptraj to read-in every frame. If this last number were "2", then ptraj would read-in every-other snapshot, "10" would be every 10th snapshot and so on.

trajin ../003.SANDER/11md.trj 1 1000 1

• This will do the exact same as the first trajin cmd (command), except now we're analyzing a different trajectory - 11md.trj.

trajout 1df8.trj.strip nobox

• trajout -> tells ptraj to write a new trajectory file, combining the two trajectories - 10md.trj and 11md.trj - from trajin.
• 1df8.trj.strip -> is the name of the new trajectory to be made by trajout.
• nobox -> is essentially a house-keeping cmd, where the periodic box information will just be neglected. Unless using CHARMM files, this ought to not be an issue.

strip :WAT

• strip -> instructs ptraj to disappear those objects named "WAT" ':WAT

• So you're left with a file "ptraj.concatenate.strip.trj" with the following in it:

trajin ../003.SANDER/10md.trj 1 1000 1
trajin ../003.SANDER/11md.trj 1 1000 1
trajout 1df8.trj.strip nobox
strip :WAT

RMSD

RMSD - root mean-square deviation - can be used to measure the distance an object moves relative to a reference object. For example, one could use an RMSD analysis to measure the movement of the alpha-carbon atoms in the active site of a protein, using the experimental structure as the reference structure (ptraj will measure the RMSD between each object specified in the ptraj script - see below) where ptraj will by default fit the two structures, aligning them as much as possible. nofit is used to turn this function off.

ptraj.2.in

 trajin 1df8.trj.strip 1 2000 1
 trajout 1df8.com.trj.stripfit
 reference 1df8.com.gas.leap.crd

• reference -> tells ptraj that you want to specify a reference file - snapshot - for which to compare your trajectory (file with many snapshots) to.
• 1df8.com.gas.leap.crd -> is the reference file. This file is very important and you ought to be thoughtful about your selection of this file. Usually, when possible, one wants to use the experimental structure as the reference. Referencing the experimental structure 'usually' provides the most informative results. But, if done thoughtfully, a non-experimental reference could be informative, too...

 rms reference out 1df8.rmsd.CA.txt :1-118@CA

• rms -> tells ptraj you want to perform an rms analysis
• reference -> tells traj to use the reference file, specified in the previous line
• out -> tells ptraj to create a temporary file out for which to store calculations during the analysis
• 1df8.rmsd.CA.txt -> is the name of the file with the RMSD analysis results. This is the file you will use with your plotting program..
• :1-118@CA -> tells ptraj to analyze the RMSD of the alpha-carbon atoms CA residues 1-118.

So when you're done, you're left with:

trajin 1df8.trj.strip 1 2000 1
trajout 1df8.com.trj.stripfit
reference 1df8.com.gas.leap.crd
rms reference out 1df8.rmsd.CA.txt :1-118@CA

Keep Only Streptavidin from 1df8.com.trj.stripfit

ptraj.4.in

trajin 1df8.com.trj.stripfit 1 2000 1
trajout 1df8.rec.trj.stripfit
strip :119

• We've just stripped residue 119 (Biotin) from the 1df8.com.trj.stripfit file, which we've previously stripped of water

Keep Only Biotin from 1df8.com.trj.stripfit

ptraj.5.in

trajin 1df8.com.trj.stripfit 1 2000 1
trajout df8.lig.trj.stripfit
strip :1-118

• Strip everything, keeping only the protein, Streptavidin

Biotin Notes

Download PDB Here and view it's details Here.