Such a "twinning operator" can also indicate that you spacegroup has an
extra symmetry operator (h,-h-k,-l)
That is in fact one of the symmetry operators for P3i21 H32 P6i22
Have you solved the structure in the lower symmetry and is that missing
density properly generated by this operator?
Eleanor
Benirschke, Robert C. wrote:
Dear all,
I am trying to solve the structure of a protein complex, via MR, and
when the phasing is complete there is 1/3 of the unit cell that is
missing electron density. The density present looks very good and
shows helices in regions that were disordered in my NMR model,
suggesting that it is correct. I have also tried phasing as P1, C2,
P3, and P6 all yielding the missing density. I have tested for
twinning, thinking this might be the problem, using the Yeates server
and it shows that there is partial twinning with a fraction of .48 and
a transformation matrix of 1 0 0 -1 -1 0 0 0 -1. Also, 3 other
crystals have showed this missing density and had twin fractions from
.46-.48. Although it is twinned, I am not sure how this would cause
an entire region of the unit cell to be missing and the crystal would
not be able to form with an entire layer not ordered. So my question,
to whoever is still reading, is what could be going on here? Thanks
in advance.
Robert
