Insane - A simple, versatile tool for building coarse-grained simulation systems

Insane (INSert membrANE) is a versatile tool to build coarse-grained simulation systems containing solutes, lipid bilayers, and/or solvents. It is initially aimed at the Martini force field but can be used for other models. It can write PDB or gromacs files.

Using insane, you can build a system containing a transmembrane protein included in a lipid bilayer, with water and ions with the following command line:

insane \
    -f cg1a0s.pdb \
    -l POPC \
    -sol W:90 -sol WF:10 \
    -salt 0.8 \
    -o system.gro -p topol.top

Installation

Insane can be installed either as a single-file program, or as a python module.

Install insane as a single-file program

Insane depends on python (either version 2 or 3) and on the numpy python library. Make sure you have these two requirements installed:

python -c 'import numpy'

If this command line outputs an error message, you need to instal either python or numpy.

Download the latest version of insane as a single executable.

Run insane: ./insane -h.

Install insane as a python module

Insane is available on pypi and can be installed using pip. To install insane for the current user, run

pip install --user insane

Pip installs the insane in ~/.local/lib/python<version>/site-packages, where <version> is the version of python. Check that the directory exists and that it is in your PYTHONPATH. The insane program is installed in ~/.local/bin, make sure this directory is in your PATH.

To install insane system wide, run

sudo pip install insane

We recommend the use of python virtual environments. Read more about them on the MDAnalysis website.

Quick start

Create a simple lipid bilayer

The following command creates a hydrated POPC bilayer:

insane -l POPC -d 10 -dz 7 -sol W -o bilayer.gro -p topol.top

The -l argument tells insane to include the given lipid. The number of lipids to include is determined from the area per lipid and the size of the box; the default area per lipid is 0.6 nm².

With -d and -dz, we specify the dimensions of the box. Here we create a hexagonal prism box where images are separated by 10 nm in the XY plane, and 7 nm in the Z dimension. The shape of the box can be changed with the -pbc argument.

The -sol argument tells insane to include some solvent in the box. Here we include Martini water. The total amount is defined from the free volume of the box, and the solvent diameter (0.5 nm per default).

The -o and -p arguments specify the output of the program. With -o bilayer.gro, insane will write the system structure in a GRO file usable with gromacs. Insane can also write PDB files if the output file has the '.pdb' file extension. With -p topol.top, insane will write a template TOP file to be used with gromacs. If the -p argument is omitted, insane writes the content of the system on the standard output in a form that can be appended at the end of an existing TOP file.

Create a more complex bilayer

Insane can build lipid mixtures. Here we build a ternary mixture containing a fully saturated lipid (DPPC), a polyunsaturated lipid (dilinoleyl-phosphatidylcholine, called DIPC in the Martini force field), and cholesterol.

insane \
    -o bilayer.gro -p topol.top \
    -x 20 -y 20 -z 10 \
    -l DPPC:4 -l DIPC:3 -l CHOL:3 \
    -sol W:90 -sol WF:10

The periodic box can be defined in multiple ways. Here we build an orthorhombic box by setting the X, Y, and Z axes separately with -x, -y, and -z, respectively.

The -l option can be provided multiple times to setup multiple lipid types. Here we setup DPPC, DIPC, and cholesterol with a 4:3:3 ratio.

The -sol option can also be provided multiple times. Here the solvent is composed of 90% of regular Martini water and 10% Martini anti-freeze water.

Solvate a protein

Insane can setup protein systems. Here we create a box of solvent around a protein. Note that insane does not prepare the protein itself. Use martinize to coarse grain a protein structure.

insane -o system.gro -p topol.top -f protein.pdb -d 7 -sol W -salt 0

Solutes, including proteins, can be read from a GRO or a PDB file provided with the -f argument.

With the -d 7 argument, insane builds the periodic box such that the distance between two periodic images is greater than 7 nm. By default, in the absence of a membrane, insane builds a rhombic dodecahedral box. Setting the periodic box with -box, or setting the box geometry with -pbc, overwrite that default.

If the -salt argument is set, insane will add ions to the system. With -salt set to 0, insane will add enough chloride or sodium ions to neutralize the system charge. If -salt is set to any positive value, it is read as the concentration of ions in molar.

Insert a protein in a membrane

Now that we have seen how to build a membrane and how to build a protein system, we can insert a protein in a lipid bilayer.

insane \
    -o system.gro -p topol.top \
    -d 10 -pbc hexagonal \
    -l POPC -sol PW \
    -f protein.gro -center

Here, the protein structure we give with the -f argument is centered in the box along the Z axis with the -center argument.

We build this system with Martini polarizable water using -sol PW.

With the -pbc option we set the shape of the periodic box to a prism with a hexagonal base.

Changing templates

Templates for both Martini 2 and 3 molecules are predefined within insane, use the -ff M2 or -ff M3 to switch between them. Specific template versions can also be specified directly in the lipid name e.g. use -l M3.POPC instead of -l POPC.

Definitions of lipid templates are stored in the insane/lipids.dat file and can be viewed and edited there.

Get help

Get the list of all the arguments by running insane -h.

You can get additional help in the "Tools" section of the Martini forum.

As well as access tutorials using insane in Martini 2 membrane tutorials and Martini 3 membrane tutorials.

Contribute

Insane is hosted on Github. Please, report there any issue you encounter.