[gmx-users] Force Field for Bilayer Simulations with Cholesterol and Proteins

[Piggot T.]

Hi David,

Firstly I would say, is there any reason why you need to use the Berger/Höltje/GROMOS force field combination? There are several other options available that I can think of which may be easier/better for you. You could use the Slipids (with an AMBER force field for the protein), CHARMM36 for all of the components of your system, or if you do want to stick with a united-atom force field, you could still use one of the GROMOS force fields ((e.g. 54A7) with the GROMOS-CKP lipids and the consistent cholesterol parameters that you can download from the manual entry of the automated topology builder. I haven't ever simulated cholesterol so I cannot really recommend which may be better than others for this molecule, but there will be plenty of literature out there to look at regarding this.

Secondly, if you do want to stay with the Berger/Höltje/GROMOS combination, you could probably add the missing atomtypes to the GROMOS force field you wish to use. I would strongly advise against using the old 'ffgmx' force field, this has been shown to behave pretty poorly for proteins. Do be careful in doing this addition of atomtypes, as the GROMOS force fields are different from the all-atom force fields in as much as the atomtypes have multiple van der Waals interaction parameters used for interactions with different atomtypes. Some of the GROMOS papers describe this in far more detail.

Just some of my thoughts, hopefully of some use!

Cheers

Tom
--
Dr Thomas Piggot
University of Southampton, UK.


________________________________________
From: gromacs.org_gmx-users-bounces at maillist.sys.kth.se [gromacs.org_gmx-users-bounces at maillist.sys.kth.se] on behalf of Ollila Samuli [samuli.ollila at aalto.fi]
Sent: 09 May 2014 11:42
To: gmx-users at gromacs.org
Subject: Re: [gmx-users] Force Field for Bilayer Simulations with Cholesterol and Proteins

Hi,

I used ffgmx.itp. It contains CB.

BR,
Samuli Ollila

________________________________________
From: gromacs.org_gmx-users-bounces at maillist.sys.kth.se [gromacs.org_gmx-users-bounces at maillist.sys.kth.se] on behalf of David Ackerman [da294 at cornell.edu]
Sent: Wednesday, May 07, 2014 10:30 PM
To: Discussion list for GROMACS users
Subject: Re: [gmx-users] Force Field for Bilayer Simulations with Cholesterol and Proteins

Thank you for your advice.

Which force field was used? I have downloaded the cholesterol parameters
from Höltje et al, but atomtypes like CB do not exist in the force field I
am using (53a6). Did you change these to other atomtypes as well, or were
you using a force field that included them?

-David


On Wed, May 7, 2014 at 8:59 AM, Ollila Samuli <samuli.ollila at aalto.fi>wrote:

> Hi,
>
> In my understanding the CH2-LP2 attraction is stronger than LP2-LP2
> attraction in the Berger/Höltje combination you described. If you then have
> CH2 groups in cholesterol and LP2 groups in lipids, it might lead to too
> condensed bilayer. I think that the related issue is discussed here:
>
> http://dx.doi.org/10.1088/0953-8984/18/28/S07
>
> and here:
>
> http://dx.doi.org/10.1039/C2CP42738A
>
> we have changed the CH2 groups in cholesterol to LP2 groups and compared
> the results quite extensively to the NMR measurements.
>
> BR,
> Samuli Ollila
>
>
> ________________________________________
> From: gromacs.org_gmx-users-bounces at maillist.sys.kth.se [
> gromacs.org_gmx-users-bounces at maillist.sys.kth.se] on behalf of David
> Ackerman [da294 at cornell.edu]
> Sent: Monday, May 05, 2014 7:39 AM
> To: gromacs.org_gmx-users at maillist.sys.kth.se
> Subject: [gmx-users] Force Field for Bilayer Simulations with Cholesterol
>       and Proteins
>
> Hello,
>
> I have been performing simulations of multi-component bilayers using
> parameters described in the following paper:
> http://www.ncbi.nlm.nih.gov/pubmed/23470157. They use the ffgmx forcefield
> with Berger lipid parameters included. They also use cholesterol from
> Holtje et. al (
> http://www.sciencedirect.com/science/article/pii/S000527360100270X), which
> was parameterized for the ffgmx force field.
>
> I noticed that unlike the KALP-15 GROMACS tutorial which suggests deleting
> the default lipid-gromos Berger interactions, the authors kept those
> interactions in the force field. In light of newer force fields, are these
> older force fields wither Berger parameters still acceptable? The
> cholesterol model seems commonly used, so I am unsure how to use
> cholesterol with a newer force field.
>
> Furthermore, if I were to include proteins in the simulation, would I still
> be able to use the same ffgmx force field with Berger parameters (including
> lipid-gromos interactions)?
>
> Thank you,
> David
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