On 20 Aug 2008, at 8:11, Wim Burmeister wrote:
> James Pauff a écrit :
>> Hello all,
>>
>> I have a refined structure at 2.6 angstroms that at about 73%
>> completeness at this resolution. The I/sigma is about 2.0 at 2.6
>> angstroms, and the omit density for my ligands is great contoured
>> at 3.0sigma. My Rcryst is 19 or so and the Rfree is 24.5 or so.
>>
>> HOWEVER, my mean B value is 13.9, whereas my other 2 structures
>> (at 2.2 and 2.3 angstroms, same protein, >95% completeness) have
>> mean B values of 22+. Any suggestions as to what is going on
>> here? I'm having trouble explaining this.
>>
>> Thank you,
>> Jim
>>
>>
>>
>>
>>
> Dear Jim,
>
> probably you did not collect your data to the highest possible
> resolution. Did you use an inhouse source? You would expect that a
> crystal with an average temperature factor of 14 A2 would diffract
> to 1.6 A on a synchrotron source.
>
> Regards
>
> Wim
>
Indeed.
I could also speculate that if the completeness is 75% because 25%
of the *weakest* reflections are missing that would artificially show
a lower B factor. Did you look at the actual Wilson B plot - if not
do, you can learn a lot of simple things from this graph (its there
in the Truncate output, usually part of a scaling run, after SCALA)
A.
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