[phenixbb] P43212 spacegroup change to C2221?

Leigh Allen c.leigh.allen at gmail.com
Tue Aug 25 09:47:27 PDT 2009

Hello Phenix users.

I recently solved the structure of my enzyme using SAD to a resolution of
1.9A.  The R values were 0.19/0.25 and the space group was P43212 with a
unit cell ~80, 80, 220.

I then starting collecting datasets cocrystallized with ATP analogs and
noticed that a lot of my datasets have a different unit cell when scaled in
P43212.  It comes out to be ~60, 60, 220 and I can NOT get a solution in
Phaser with this data.  If I scale it in C2221, then the unit cell is the
same (80, 80, 220), but upon refinement, the R factors don't go much below
0.26/0.32.  Has anyone ever seen something like this happen?  I'm unsure if
I should feel like the solution is C2221 since there are space groups of
higher symmetry with similar residuals that seem plausible in indexing just
the smaller unit cell. Should I keep trying to get a solution out of the
data that leads to different unit cell parameters, but has higher symmetry?

Xtriage seems to find twinning, but I think it's from NCS since my ASU
contains a homodimer.  I could also be wrong about this...

Thanks in advance for any advice!

Leigh Allen
Ph.D Candidate
McCafferty Lab
Duke University
Department of Chemistry
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