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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.
James H. Naismith | Research mailto:email@example.com
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