[gmx-users] Re: Gromacs 54a7 force field

[Justin Lemkul]

On 7/18/12 6:57 PM, Thomas Piggot wrote:
> Hi,
>
> Justin, I am interested by your comments regarding the CHARMM lipids. In
> particular can you elaborate as to why you think that the CHARMM lipids are
> better than the united-atom ones (such as Berger and several GROMOS variants).
>

I think there's nothing wrong with Berger lipids, and I myself use them 
routinely.  They do a decent job of reproducing lipid behavior, no question.  My 
own use is motivated by historical reasons primarily since I began work with 
them many years ago (also around the time that 53A6 was all shiny and new) and 
I'm trying to keep consistent.  It seems to me that the CHARMM36 parameters are 
very thoroughly validated and are very modern.  The Berger lipids were developed 
a long time ago using very short (by modern comparisons) simulations and old 
parameter sets that have since been improved upon.  There are numerous 
reasonable lipid models out there, to be sure.

> As for the original question, the modifications in going from GROMOS 53A6 to
> 54A7 will not influence the combination with the Berger lipid parameters, if the
> most common approach of using the parameters from the 'lipid.itp' file is taken.
> The interactions between protein and lipid will remain the same, with the van
> der Waals interactions between the protein and lipid treated using the GROMOS87
> parameters as defined in lipid.itp. From my experiences I would strongly
> recommend using 54A7 over 53A6, as we have seen instability in short helices in
> 53A6 that is not reproduced when simulating the same systems with several other
> force fields.
>

I agree with this, I'm just a stickler for validation.  A test system using this 
force field combination should certainly replicate some known behavior.  It's 
generally accepted that any Gromos derivative is compatible with the Berger 
parameters, but I've never seen anyone demonstrate it systematically aside from 
their own usage for particular cases.

> For the 'best' force field to choose when simulating a membrane-protein system,
> there is no definitive answer that I (or anyone else) can give you (yet). My own
> opinion is that currently CHARMM36 is probably too slow (given that I would
> strongly recommend the use of the CHARMM TIP3P water model with this force
> field) and that the all-atom protein force fields are probably better than the
> united-atom ones. This means that I would (for a PC membrane) use Berger for the
> lipids with OPLS-AA/L or an AMBER force field for the protein. This is just my
> (current) opinion though, I strongly suggest doing lots of your own reading
> before making your mind up.

Indeed.

-Justin

-- 
========================================

Justin A. Lemkul, Ph.D.
Research Scientist
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

========================================