Re: Temperature dependent unfolding..

From: Neema Salimi (nsalimi_at_msg.ucsf.edu)
Date: Thu Sep 06 2007 - 12:45:22 CDT

Extrapolations from room temperature (or slightly higher) are pretty
worthless for simulations at these temperatures. I've had proteins
bigger than ubiquitin that unfold far slower at room temperature that
unfold just fine at 500K. And extrapolations based on (delta)Cp are
equally meaningless, as for some of the proteins I've looked at, says
they would unfold in less than 1 picosecond, obviously quite impossible.

On Sep 6, 2007, at 4:34 AM, Giovanni Settanni wrote:

> Hi Arun,
>
> did you (very very roughly) check the expected unfolding time of
> ubiquitin at high temperature extrapolating the Arrhenius's law
> (with the brutal assumption that there are no solvent phase
> transitions as you would not see them in the simulations)? It may
> be much larger than
> 12ns, and your simulations may be correct (even if they provide no
> information about the unfolding pathways!). Ubiquitin has a very small
> unfolding rate at 300K (0.001 s-1), I do not expect it to increase by
> almost 12 orders of magnitudes with temperature alone. The authors
> of the phys rev E probably did a temperature AND pressure induced
> unfolding.
> Cheers
>
> Gianni
>
> --
> Giovanni Settanni
> Centre for Protein Engineering
> MRC Centre
> Hills Road,
> Cambridge, UK
> CB2 0QH
> Phone: +44 1223 402133
> Fax: +44 1223 402140
>
>
> Arun Krishnan wrote:
>> Hi Monika,
>> I have uploaded all my config files to my website. You can get
>> them from here:
>> a) energy minimization: http://www.iab.keio.ac.jp/~krishnan/
>> downloads/min.namd <http://www.iab.keio.ac.jp/~krishnan/downloads/
>> min.namd>
>> b) heating to 300K: http://www.iab.keio.ac.jp/~krishnan/downloads/
>> heating.namd
>> c) equilibration @300K: http://www.iab.keio.ac.jp/~krishnan/
>> downloads/equilibrate_300K.namd
>> d) production @300K: http://www.iab.keio.ac.jp/~krishnan/downloads/
>> production_300K.namd <http://www.iab.keio.ac.jp/~krishnan/
>> downloads/production_300K.namd>
>> e) heating to 520K: http://www.iab.keio.ac.jp/~krishnan/downloads/
>> heating_to_520K.namd
>> f) equilibration @520K: http://www.iab.keio.ac.jp/~krishnan/
>> downloads/equilibrate_520K.namd
>> g) production @520K: http://www.iab.keio.ac.jp/~krishnan/downloads/
>> production_520K.namd <http://www.iab.keio.ac.jp/~krishnan/
>> downloads/production_520K.namd>
>> I ran these under NPT.. so some of the comments in the files might
>> not make sense. (These were put in when I was initially doing an
>> NVT ensemble).
>> Do let me know if you see anything wrong.
>> Thanks in advance.
>> Cheers,
>> Arun
>> On 9/5/07, *Monika Sharma* <mon_sharma_at_research.iiit.ac.in
>> <mailto:mon_sharma_at_research.iiit.ac.in>> wrote:
>> hii!!
>> can you just write your conf file here the last part of the
>> run?There
>> might be some problem in going from 300K to 500K.
>> regards,
>> monika
>> Arun Krishnan wrote:
>> > Dear NAMD list users,
>> >
>> > I have been trying to carry out unfolding simulations of
>> Ubqiuitin. I
>> > use the top_all22_prot.inp and par_all22_prot.inp topology and
>> > parameter files.
>> > I did the following steps:
>> >
>> > a) Energy minimization
>> > b) Heating to 300K
>> > c) Equilibration for 50ps NPT
>> > d) Production run @300K for 1ns. NPT
>> > e) Heating to 500K
>> > f) Equilibration for 50ps NPT
>> > g Production run @500K for 12ns NPT
>> >
>> > Very surprisingly, I don't see the RMSD values changing
>> (with respect
>> > to the final equilibrated frame at 300K) by greater than 4-5
>> > Angstroms. This is very weird. There is a paper in Physical
>> Review E,
>> > 72, 051928, 2005 "Unfolding dynamics of the protein ubiquitin:
>> Insight
>> > from simulation" where they achieved drastic unfolding
>> within 1ns
>> > for ubiquitin at 520K. I followed what they did and tried
>> at 520K
>> too.
>> >
>> > I have used NPT throughout.. but I also used NVT and NVE
>> ensembles..
>> > and in all cases it seems to be very stable. Does anyone
>> have any
>> > pointers to what I might be doing wrong?
>> >
>> > Thanks in Advance,
>> >
>> > Arun
>> > -
>> >
>>
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>
>
>

Neema Salimi
nsalimi_at_msg.ucsf.edu

University of California-San Francisco
Graduate Group in Biophysics
Agard Lab
http://msg.ucsf.edu/agard/
Lab Phone: (415) 476-5143

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