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Re: aniso scaling

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Just a comment

I am always unhappy about removing positional ncs retraints at all.
Agreed there may be real differences but these can be satisfactorily 
treated by excluding them from restraint. Domain Domain movements are 
dealt with by having two matrices of restraint. Improperly restraining 
NCS will mess things up no doubt. So in that case removing the restraint 
makes things better, but often things could be even better by specifying 
the groups for restraint with more precision.

Removing NCS restraints however will generate differences but are they 
real? We all sign up to the proposition that bond length, angles etc are 
not influenced by crystal packing. Surely then when we are dealing with 
two chemically identical molecules, we should expect them to have 
identical structures. Thus deviating from that null hypothesis should 
really only be done when we have unambigious information to the contrary 
(and to only the minimum extent). 

As to the B-factor, as has been said the Wilson plot tells you what you 
should expect. This can be misleading where you have processed free 
space rather than data but is a good guide. 
I think the problem is that we grew up with an idea high 
res = low B. This was based on our experience of crystals which diffracted 
in capills in the lab 2.0A. These are rocks compared to frozen crystals 
which diffract to 2.1A at the synchrotron (which under equivalent experimental 
conditions may be lucky to get to 3A). I have seen (and a casual trawl of 
the PDB shows this to be far from unique) what in the past would be a 
problem B of 40+ at 2.2A for frozen xtals collected at the synchrotron.


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