structure AND thermodynamics

Mon May 23 21:24:41 EST 1994

Dear Chris:

> technique for thermodynamics is scanning calorimetry. Unfortunately, it seems
> that the current calorimeters are not entirely satifactory, as we could all
> read in an article written by Julian Sturtevant in the last issue of Curr.
> Op. in Struct. Biol. (1994, 4, 69-78). Basically, the accuracy one is
> interested in is 10**-6 times the overall heat expended in the calorimetric

We are trying to study the relationship between structure and stability
by combining crystallographic, calorimetric and hydrgen exchange-NMR
data of small globular proteins.  Julian Sturtevant has contributed to
the calorimetry arena for over 50 years and does a good job of
describing the problems in the COSB review.  When it comes to DSC of
proteins, one is basically interested (amongst other things!) in
calculating the heat capacity change (dCp) associated with thermal
denaturation or unfolding.  There are significant problems in measuring
dCp from a single DSC scan.  One usually obtains this parameter by
doing DSC scans as a function of pH and plotting the enthalpy change
versus the melting temperature (dCp = ddH/dT).  Also, there is a lot of
debate about the information content of dCp in relation to protein
folding.  This means that the problem still remains largely unsolved.
Well, without going into further details, let me tell you that
sensitivity is but one of the many things that need careful
consideration when addressing DSC of proteins.

> experiment. Dr. Sturtevant questions whether it will be possible to make
> significant improvements of scanning calorimeters.

There are two companies in the U.S. that manufacture scanning
calorimeters suitable for doing DSC on macromolecules.  Microcal Inc.,
Northampton, Mass and Hart Scientific, Utah.  I have extensively used
the Microcal instrument and was told recently by the experts at this
company that significant improvements have been made in both sensitivity
and reproducibility.  You might want to contact Microcal 
for additional details.

> My question is whether anyone of you ever has tried a completely new type
> of calorimeter invented by Dr. Hans Coufal (IBM). His calorimeter uses a 
> Who can shed a light on this? Or, who can refer me to experts in the field?

Well, I heard something in reference to Dr. Coufal at a meeting
recently, but am not familiar with the details of this design.  I
suggest that you contact the BIOCALORIMETRY Center at Johns Hopkins
University directed by Dr. Ernesto Freire to determine if they have
additional info. on this matter (bcc at  I am also
aware of a high sensitivity calorimeter developed at NIH, but it works
by a mechanism different from that you have described.

> It would be extremely beneficial if protein crystallographers could also
> gather thermodynamic data on their mutant proteins. In this way, a large
> database of EXPERIMENTAL data on energetics combined with STRUCTURES would 
> become available. I believe this will be of crucial importance for cracking
> the Holy Grail of protein folding.

The system we use (yeast cytochrome c) has the advantage that we have
many mutants, their high res. crystal structures and hydrogen exchange
data in solution.  These in conjunction with the DSC data can aid in
comparing local and global protein stability from a structural point of

Well, there is a lot of DSC data published on both reversible and
irreversible protein denaturation and I would recommend that you keep an eye
out for papers published from the following labs:  Julian Sturtevant,
Peter Privalov, Ernesto Freire, Nick Pace, Jim Lepock and Pedro Mateo
amongst others.  Finally, the best review, IMO, on the various aspects
of DSC was published in Ann. Rev. Phys. Chem. [1987] 38, 463-488.  

Feel free to contact me if you have additional questions or comments.  

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