Frozen vs Room temp. crystals

Brad Poland brad at helix0.chem.iastate.edu
Wed Apr 17 11:07:32 EST 1996


Bill Hunter (wnh at spec.ch.man.ac.uk) wrote:
: Dear Mark,

: Do you see a change in unit cell dimensions? I would be interested to know
: about MFID v resolution for your 2 data sets?  Does a reduction in
: mobility/thermal motion lead to improved scattering?  Whilst I've seen
: publications on protein models refined against data sets collected at different
: temperatures I don't recall seeing a detailed comparision of the actual data.
: Do you know of any relevant papers on the subject?

: Cheers

I've just finished collecting 2 data sets one at room temp and one at 107K.
The difference the data stats is remarkable.  Resolution increased from 3.2A
to 2.6A.  My unit cell parameters changed a little ~0.3A in axial lengths.

I am refining both models now and after several cycles of refinement
the RMSD in coordinates is ~0.15A, essentially the same structure.  My data
are much better at 107K, which I feel are do to two factors. 1) There is less
thermal motion. 2) There is less decay of the crystal in the X-ray beam.  I
was about to increase my collection time/frame by a factor of 1.5.

Also my crystals grew from PEG and I used 25% glycerol as the protected, worked perfectly.  Hope the info. helps.

brad 


--
                                                              __o      o
Brad Poland, ISU Ames, IA.                     ____/\o__   _ |/<_     <\
brad at helix0.chem.iastate.edu                              (_)| (_)   / >

Some people eat to train, I train to eat!


 




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