Greg Petsko's group did something like this about a billion years ago
(yet, strangely, I remember the paper, even though I'd be stumped if
you asked me what I had for breakfast...)
They covered the range from room temp down to very cold, using
different cryoprotectants (importantly, they were not vitrifying
their samples). I recall a plot of ADPs vs. temp that showed an
essentially linear decrease down to some temp (maybe around 150 K or
so?), after it plateaued, with no further reductions being seen at
even very low temp. They rationalized this by saying (I think) that
the decrease represented the dynamic disorder, which was damped at
low temperatures, and the plateau represented the point where static
disorder became the predominant contributor.
I remember thinking at the time that this made great intuitive sense.
I have no idea if people still buy this.
I can't put my finger on the reference, but if you start here you can
probably find your way: Ringe D, Petsko GA. Study of protein dynamics
by X-ray diffraction. Methods Enzymol. 1986;131:389-433.
On 13 May 2009, at 12:30 PM, Jacob Keller wrote:
The reason is that you've missed out one important term: the
atomic displacement parameters (B-factors), which describe a
combination of thermal motion and positional disorder between unit
cells.
A somewhat niggling point: isn't it true that the thermal motion is
insignificant at 100K? Does anybody know of a paper which
systematically measures B-factors as a function of temperature? The
asymptote of the resulting curve would represent all of the non-
thermal elements, right?
JPK
------------------------------------------------------------------------
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Patrick J. Loll, Ph. D.
Professor of Biochemistry & Molecular Biology
Director, Biochemistry Graduate Program
Drexel University College of Medicine
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(215) 762-7706
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