Agreed. Lots of thermal action is reflected in a high Wilson B and is
consistent with a low diffraction limit: if average I keeps decreasing
with resolution, it has to go below the limit of measurement at a lower
resolution than a more sedate crystal, which will have a lower B and a
higher diffraction limit.
A good way to get a reliable B factor for low resolution data is to
analyze a "relative Wilson plot." Call your crystal of interest crystal
two, and a high resolution crystal with a reliably known B factor
crystal 1. Then plot the ln of the ratio of the <I>s of the two
crystals vs rho. The plot will be linear and the intercept will give
the scale (scale = exp (-intercept/2)) for crystal 2 relative to crystal
1 and the slope will give the difference in temperature factors (=
-slope/2) between the two crystals.
I learned this procedure in the 1970s from George Reeke, who encoded it
in the late lamented ROCKS software suite, and I believe that he learned
it from one of the wizards in the Lipscomb lab during the
carboxypeptidase days.
Joe Becker
Merck Research Laboratories
-----Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of
Eleanor Dodson
Sent: Thursday, July 26, 2007 5:21 AM
To: [log in to unmask]
Subject: Re: [ccp4bb] High Wilson B
It is hard to get a resonable estimate of Wilson B with 4.5A to 3A data,
but yes - if the crystal stops diffracting at 3A that seems reasonable
to me
Eleanor
Michael Colaneri wrote:
> Dear colleagues,
>
> I have a B of 75A**2 from Wilson statistics 4.7 to 3 A res, good
> straight line. Has anyone seen a B so high in Wilson statistics?
>
> ( I understand that it is best to have higher res but I do not).
>
> Thanks.
>
> Mike Colaneri
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