This simple python3 code accompanies the paper "Membrane Stiffness is Modified by Integral Membrane Proteins" which is published in the journal Soft Matter. By making this code public we hope that other researchers will be more easily be able to reproduce our results.
If you use the code, please cite
Fowler P W, Hélie J, Duncan A, Chavent M, Koldsø H, Sansom MSP. Soft Matter 2016, 12 (37), 7792–7803. http://dx.doi.org/10.1039/c6sm01186a
You will need to install
- python 3.X
- numpy and scipy
- MDAnalysis. Version 0.8.1 used for development and testing.
On a Mac python, numpy and scipy can be easily installed using either MacPorts or Homebrew. The other python modules should already be present on your system (argparse and math).
Although the code is setup with command line flags so you can analyse your own simulation data, coordinate and trajectory files of the last 20% (i.e. 4-5µs) of the 1500 POPC coarse-grained MARTINI simulation is included in the example-trajectory/ folder. For simplicity these only contain the phosphate (i.e. PO4) beads as the code uses these to construct the two surfaces of the bilayer. Defaults in the code are setup so that if you simply run the following in a terminal
./calculate-bilayer-power-spectrum.py
It will use the same options as in the paper and analyse the small 1500 CG POPC simulation. The data files are written to
ls output-files/
output-thickness.dat output-undulation.dat
In both cases plotting column 1 against column 2 on a log-log plot will give you the power spectra shown in the upper panel of Figure 2C of the paper.
The code is also setup with command line options. To see these
./calculate-bilayer-power-spectrum.py --help
and you should get
usage: calculate-bilayer-power-spectrum.py [-h] [--pdb PDB] [--traj TRAJ]
[--phosphate PHOSPHATE]
[--output OUTPUT]
[--discard DISCARD] [--step STEP]
[--bins BINS]
optional arguments:
-h, --help show this help message and exit
--pdb PDB the name of the coordinate file to read in (e.g.
foo.pdb)
--traj TRAJ the name of the trajectory file to read in (e.g.
foo.xtc)
--phosphate PHOSPHATE
the selection text for the phosphate group (default is
'name PO4' for MARTINI CG sims)
--output OUTPUT the stem of the output file (default is 'output-
files/output')
--discard DISCARD the proportion of the trajectory to discard in the
range 0.0-1.0 (defaults to analyse the whole
trajectory i.e. 0.0)
--step STEP the size of the grid in nm (default=0.5nm)
--bins BINS divide the trajectory into this many bins (default is
to analyse the whole trajectory)