Hi Eleanor,
well, anisotropy results in artifacts in maps, with different outputs
depending on softwares and truncation or not.
There is also the fact that the definition of anisotropy can vary.
Membrane proteins are definitely affected by this pehnomenon, but a
single value of anisotropy as computed by Phaser is not linked directly
to a difference in resolution limits in an ellipsoid. (This claim might
trigger some disaproval; I've showed it for a simple approximtion of
resolution limits but others might test it with a real ellipsoid)
In any case, if you want to test out different things, I have a few
membrane proteins datasets (I kept the images) that I'd be happy to share.
Best
Vincent
Le 03/10/2022 à 13:33, Ian Tickle a écrit :
Hi Eleanor
Individually, the weights of weak data might be relatively small but
cumulatively the effect could be significant, especially if the
proportion of weak data is large, which is often the case with
anisotropic data. A large proportion of weak data in refinement
probably won't help and it might well hinder: this is the reason for
having an anisotropic cut-off.
Cheers
-- Ian
On Mon, 3 Oct 2022 at 12:18, Eleanor Dodson
<0000176a9d5ebad7-dmarc-requ...@jiscmail.ac.uk> wrote:
There have been several discussions lately where anisotropy has
been an issue.
I have always believed weak unreliable data does little harm to
refinement or maps because it is given a very low weight in any
calculation.
Weighting, in REFMAC anyway. is set partly using the Rfree for
that resolution shell.
However if the data is anisotropic would be better if those
weights were based on shells constructed taking the anisotropy
into consideration?
Or does it matter, and how could it be tested!
Eleanor
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Vincent Chaptal, PhD
Director of GdR APPICOM
Drug Resistance and Membrane Proteins Lab
MMSB -UMR5086
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