AMBER Tutorial ¶

Interactive data analysis with pytraj/cpptraj and Jupyter notebook ¶

By Hai Nguyen (BSD 2-clause) ¶

What is Jupyter notebook?¶

Direct introduction and figure from Jupyter notebook website:

"The Jupyter Notebook is a web application that allows you to create and share documents that contain live code, equations, visualizations and explanatory text. Uses include: data cleaning and transformation, numerical simulation, statistical modeling, machine learning and much more."

What is pytraj?¶

pytraj is a Python package binding to the popular cpptraj program. pytraj is written do extend the flexibility of cpptraj and to expose cpptraj's functionality to Python's ecosystem, such as numpy, pandas, matplotlib, ...

What can you learn from this tutorial¶

Use Jupyter notebook for interactive data exploration
Use pytraj to perform basis analysis such loading files to memory and do computing RMSD
Use matplotlib and pandas for analyzing output from pytraj

Requirement¶

AmberTools >= 16
If you allow AMBER to install Python distribution from Miniconda, you have most needed packages (except pandas) for this tutorial.
If not, you need to install (either using pip or conda)
- matplotlib
- jupyter notebook
Install pandas:
```
amber.conda install pandas
```
You know how to use Linux command line. If not, please check basic AMBER tutorial

Download required trajectories, topology¶

All files used in this tutorial, including this notebook, is here: tutorial_files.zip

Download it, then

mkdir tutorial
cd tutorial
unzip ../tutorial_files.zip

Start notebook¶

$ amber.jupyter notebook
(or jupyter notebook if you did not allow AMBER to install Miniconda)

You should expect to see a blank directory (or with a list of files)

Choose New --> Python 2 (or Python 3, depending on which version you're using)
You should expect to see

How to follow this tutorial? Copy and paste each command in this tutorial to the notebook, hit "Shift-Enter" to run and to create new Cell. Check Tips in the end of this tutorial for useful commands.
If you want to use the notebook remotely (run it in your remote cluster and view it in your desktop), please check remote notebook tutorial
Note: This tutorial is written in the Jupyter notebook, so you can download and run it too.

Load trajectory to memory¶

from __future__ import print_function
import warnings
warnings.filterwarnings("ignore", category=DeprecationWarning) # avoid warning message to make the notebook nicer

import pytraj as pt

traj = pt.load('data/trpzip2.gb.nc', top='data/trpzip2.ff10.mbondi.parm7')

Get some basic information about the trajectory¶

print(traj)

pytraj.Trajectory, 1201 frames: 
Size: 0.000000 (GB)
<Topology: 220 atoms, 13 residues, 1 mols, non-PBC>

Computing RMSD, using 1st frame as reference¶

In this case we are computing mass-weighted RMSD, using all non-hydrogen atoms in residues 1 to 13

data_rmsd_first = pt.rmsd(traj, ref=0, mask=":1-13&!@H*")

print(data_rmsd_first)

[  2.30050392e-07   7.92393865e-01   9.72257525e-01 ...,   2.51047183e+00
   2.44805673e+00   2.33894156e+00]

Using matplotlib to plot¶

%matplotlib inline

from matplotlib import pyplot as plt

plt.plot(data_rmsd_first)
plt.xlabel('Frame')
plt.ylabel('RMSD (Angstrom)')

<matplotlib.text.Text at 0x127834b90>

Loading reference structure¶

In this case, we are loading the NMR structure for trpzip2

# we can reuse loaded topology from `traj`
ref = pt.load('data/trpzip2.1LE1.1.rst7', top=traj.top)
print(ref)

pytraj.Trajectory, 1 frames: 
Size: 0.000000 (GB)
<Topology: 220 atoms, 13 residues, 1 mols, non-PBC>

Computing RMSD to a Reference¶

data_rmsd_ref = pt.rmsd(traj, ref=ref, mask=":1-13&!@H*")
print(data_rmsd_ref)

[ 1.28171363  0.98184973  0.95976186 ...,  2.1723379   2.21177339
  2.10760399]

Plotting two RMSDs¶

We can plot rmsd to 1st frame (previously calculated) and rmsd to reference (NMR)

plt.plot(data_rmsd_first, label='to first')
plt.plot(data_rmsd_ref, label='to NMR')
plt.xlabel('Frame')
plt.ylabel('RMSD (Angstrom)')
plt.legend()

<matplotlib.legend.Legend at 0x12ae74c90>

Computing pairwise RMSD for specific snapshots¶

# compute pairwise RMSD for first 50 snapshots and skip every 10 frames
mat = pt.pairwise_rmsd(traj, mask=":1-13&!@H*", frame_indices=range(0, 500, 10))
print(mat)

[[ 0.          0.81742334  0.88945633 ...,  2.52540493  2.44746494
   2.83389616]
 [ 0.81742334  0.          0.92505556 ...,  2.42510176  2.32717562
   2.82156968]
 [ 0.88945633  0.92505556  0.         ...,  2.34702587  2.26490974
   2.60315514]
 ..., 
 [ 2.52540493  2.42510176  2.34702587 ...,  0.          1.00938892
   1.4123441 ]
 [ 2.44746494  2.32717562  2.26490974 ...,  1.00938892  0.          1.39651227]
 [ 2.83389616  2.82156968  2.60315514 ...,  1.4123441   1.39651227  0.        ]]

plt.imshow(mat, cmap='jet')
plt.xlabel('Frame')
plt.ylabel('Frame')
plt.colorbar()

<matplotlib.colorbar.Colorbar at 0x12aec9790>

Computing dihedral angles¶

In this case, we are computing phi and psi angle for residues 2 to 12. We tell pytraj to convert raw data to pandas's DataFrame to better visualization in notebook

phipsi = pt.multidihedral(traj, resrange='1-12', dihedral_types="phi psi", dtype='dataframe')

Pretty display data¶

In this case, we only display a part of the data

phipsi[['phi_4', 'psi_4', 'phi_5', 'psi_5']].head(5)

Getting some basic info¶

phipsi[['phi_4', 'psi_4', 'phi_5', 'psi_5']].describe()

Plotting dihedral¶

In this case, we are plotting Psi dihedral for residue 4 (TRP)

plt.plot(phipsi['psi_8'], '-bo', markersize=3, linewidth=0)
plt.xlabel('Frame')
plt.ylabel('Phi4')

<matplotlib.text.Text at 0x12c783d90>

Get some information about the structure¶

top = traj.top

for residue in top.residues:
    # Note: In python, 0-based index is used.
    # For example: SER0 should be first residue
    print(residue)

<SER0, 13 atoms>
<TRP1, 24 atoms>
<THR2, 14 atoms>
<TRP3, 24 atoms>
<GLU4, 15 atoms>
<ASN5, 14 atoms>
<GLY6, 7 atoms>
<LYS7, 22 atoms>
<TRP8, 24 atoms>
<THR9, 14 atoms>
<TRP10, 24 atoms>
<LYS11, 22 atoms>
<NHE12, 3 atoms>

list(traj.top.atoms)[:10]

[Atom(name=N, type=N3, atomic_number=7, index=0, resid=0),
 Atom(name=H1, type=H, atomic_number=1, index=1, resid=0),
 Atom(name=H2, type=H, atomic_number=1, index=2, resid=0),
 Atom(name=H3, type=H, atomic_number=1, index=3, resid=0),
 Atom(name=CA, type=CX, atomic_number=6, index=4, resid=0),
 Atom(name=HA, type=HP, atomic_number=1, index=5, resid=0),
 Atom(name=CB, type=CT, atomic_number=6, index=6, resid=0),
 Atom(name=HB2, type=H1, atomic_number=1, index=7, resid=0),
 Atom(name=HB3, type=H1, atomic_number=1, index=8, resid=0),
 Atom(name=OG, type=OH, atomic_number=8, index=9, resid=0)]

Tips¶

Run bash command: Use !

! echo Hello

Hello

How to run this notebook?
- Run all commands: Cell -> Run All
- Run each Cell: Ctrl-Enter
- Run each Cell and jump to next Cell: Shift-Enter
How to save all commands to Python script: Choose File -> Download as -> Python (.py)
How to save figures in this notebook: Right click and choose Save image as (or similiar command)
More info? Choose Help -> Keyboard Shortcuts