Hi
Many years ago I coded up integration using anisotropic resolution
limits for Mosflm - it seemed to work well, but the refinement
programs available at the time really didn't like huge regions of
reciprocal space having no data in them - they preferred to have
measurements there with sigmas, even if the measurements were just
background. I thought my implementation was rather elegant, since it
integrated a rather nicely formed ellipsoidal region of reciprocal
space.
So although the code is still there, and it still works, I don't make
a big deal about it. If the refinement programs are happy to deal
with the unmeasured data (in the directions where the crystal doesn't
diffract so well), I'm happy to put the effort in to resurrect it.
As for how the anisotropy occurs, there are a few good reasons; as
Fred said, the illuminated volume of the crystal can contribute.
I think another point is that there is no reason why (for a non-cubic
crystal) the order in the crystal should be isotropic; for example,
if you have molecules that are approximate prolate spheroids (think
rugby ball, or football for our American readers), they can obviously
pack better with their long axes aligned, but the orientation about
that long axis can be rather less well defined. The diffraction is a
reflection (ahem) of the internal order...
Hi,
I also have a question concerning anisotropic data. Collected a
data set and the best crystal gave highly anisotropic diffraction
patterns ( 3.7 A - 5.8 A). So my first question is how to handle
these data. I got only experience with "normal data" using the
ccp4 suite. Are there any program specially for these kind of
data? There are?
The second question is how anisotropic data occur? The protein I
work with has a tetragonal sg with a=b= 86.0 and an extremely long
c axis of 651 A. Secondary Structure prediction suggest a lot of
beta strands. How can I explain the anisotropy (for my own
interest and my thesis)?
Thank you very much.
Marie
Harry
--
Dr Harry Powell,
MRC Laboratory of Molecular Biology,
Hills Road,
Cambridge,
CB2 0QH
