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Re: [ccp4bb]: Thermostability vs Structure



Well, I meant "The stability is influenced by both enthalpic (various non-covalent interactions)  and entropic contributions of the protein and water molecules".
----- Original Message -----
From: Benny Yiu
Sent: Wednesday, December 05, 2001 1:22 AM
Subject: Re: [ccp4bb]: Thermostability vs Structure

Protein folding is entropy-driven. The native state is relatively stabilised when water molecules are released from hydrophobic groups upon folding. As temperature increases, both the enthalpy and entropy of unfolding follow as water molecules are "loosened" at the denatured state. The stability is influenced by both enthalpic and entropic contributions from various non-covalent interactions of the protein and water molecules.
 
I agree with Mischa that we need carefully designed mutants, which is needed to find out if we need to break a particular interaction to allow the protein to reach the unfolding transition state.
 
What's the thermostability of the "normal" oxidases like?
 
Benny
----- Original Message -----
Sent: Wednesday, December 05, 2001 2:13 AM
Subject: Re: [ccp4bb]: Thermostability vs Structure

I don't see why this is so.
If a protein unfolds with a large half life at a given temperature, then this means that
the free energy of the transition state is large.  When a salt bridge needs to be broken
to reach this transition state of unfolding, then this raises the barrier.  So why wouldn't
the analysis of the number of ionic pairs be helpful in this matter ?

Filip Van Petegem
 
 
 

Mischa Machius wrote:

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Hi Francisco,

I am afraid, your problem is close to unsolvable. The suggestions
that have been made so far are ok, but they deal with thermodynamic
aspects. From your email, however, it appears that you are looking at
the kinetics of protein unfolding. There is even less known about the
determinants of "kinetic stability" in proteins. Your observations
are absolutely in line with current concepts: most protein folding
experts would say that it is impossible to look at the native
structure of a protein and make inferences about its stability, or
how mutants might change its stability. I am afraid, the only way out
is to do a mutational analysis combined with a thorough thermodynamic
analysis.

Good luck,

Mischa

>I am dealing with a structure of an oxidase. I have relatively decent
>data till 1.7 A, and the model is practically refined. The protein is
>very thermostable with a half life of 2 hours at 80ºC.
>
>I have compared the structure with other "normal" oxidases, and I am not
>able to find suitable differences to explain thermostability in terms of
>structure. I have analyzed presence of disulfide bridges, salt bridges,
>packing , etc ....
>
>Is/was anybody dealing with a similar problem ?. What should be the
>factors to analyze for the explanation of thermostability ?

--
----------------------------------------------------------------------------
Mischa Machius, PhD
Assistant Professor
University of Texas Southwestern Medical Center
Department of Biochemistry
5323 Harry Hines Blvd.                                Tel: +1 214 648 9760
L4.250                                                Fax: +1 214 648 8954
Dallas, TX 75390-9038, U.S.A.     Email: Mischa.Machius@UTSouthwestern.edu
----------------------------------------------------------------------------

-- 


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Filip Van Petegem                 
Laboratory for Protein Biochemistry and Protein Engineering
Department of Biochemistry Physiology and Microbiology
K.L. Ledeganckstraat 35                Tel: (32)-9-264-5127
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