[gmx-users] Martini force field: elastic network

[Tsjerk Wassenaar]

Hi Hualin,

The elastic network should work; the help should be updated...
Note that only the 'elnedyn' method has really been tested.

Cheers,

Tsjerk

On Oct 14, 2011 7:11 PM, "Li, Hualin" <Hualin.Li at uth.tmc.edu> wrote:

Hi,Xavier,

    Thank you for your reply.  The method I used is from previous tutorial,
which goes like this:

" Martini + simple elastic network
The first option to help preserve higher-order structure of proteins is to
add to the standard Martini topology extra harmonic bonds between non-bonded
beads based on a distance cutoff. Note that in standard Martini, long
harmonic bonds are used to impose the secondary structure of extended
elements (sheets) of the protein.
1. Generate a coarse-grained PDB structure you want to use as the reference
structure.
2. Generate a list of distances between all beads within a certain
distance.The GROMACS tool genrestr is well suited for this. First generate
an index file containing only those beads you want to consider, the standard
option would be the backbone beads.
genrestr -f cg.pdb -n index -constr -o constraints
3. Select those restraints you want to keep, based on a lower and upper
cutoff. In adding to Martini you would not want to duplicate already
existing bonds, so the ”select restr.pl” script (protein_tutorial.tar.gz)
includes a lower cut-off value. The example below selects all instances from
the full list in ”constraints.itp” with a distance between 0.5 and 0.9 nm
and generates a harmonic bond with a force constant of 500 kJ mol-1 nm-2.
 ./select_restr.pl constraints.itp 0.5 0.9 500 > AddElBonds.itp
4. Paste the resulting file into the standard Martini topology for the
protein (protein.itp) in the section [ bonds ].
5. Proceed as before and start a production run."



  If there is any problem, what is the problem please?  In the new script
martinize.py, when typing "martinize.py -h" , this description show up

"

Elastic network: Fij = Fc exp( -a (rij - lo)**p )
 -elastic  Write elastic bonds (not working yet)
 -elnedyn  Use Elnedyn mapping and parameters with elastic network
      -ef  Elastic bond force constant Fc
      -el  Elastic bond lower cutoff: F = Fc if rij < lo
      -eu  Elastic bond upper cutoff: F = 0  if rij > up
      -ea  Elastic bond decay factor a
      -ep  Elastic bond decay power p
      -em  Remove elastic bonds with force constant lower than this
      -eb  Comma separated list of bead names for elastic bonds
     -cgo  PyMOL CGO file for elastic network visualization
"

    Is my understanding about the line "   -elastic  Write elastic bonds
(not working yet) " verbally wrong or it is already working please?

 Thank you very much for your reply? Is there any way to get the old version
of select_restr.pl please?

Thanks,
Hualin








________________________________________
From: gmx-users-bounces at gromacs.org [gmx-users-bounces at gromacs.org] On
Behalf Of XAvier Periole [x.periole at rug.nl]
Sent: Friday, October 14, 2011 11:17 AM
To: Discussion list for GROMACS users
Subject: Re: [gmx-users] Martini force field: elastic network

The website has been updated to fit a CG tutorial starting monday in
Lausanne. The manner of the c...
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