You dont say whether the molecules in the native cell form a dimer - if
so I would search with that (you may need to turn off the packing search)
Or whether there is a pseudo translation vector in the mutant form..
Or what the data analysis graphs from TRUNCATE show - are they "normal"?
Eleanor
Demetres D. Leonidas wrote:
Dear all,
we have encountered a problem in solving one mutant structure. The
mutant protein crystallizes in the same space group as the native (C2)
but the unit cell dimensions are different. These for the native
structure are 101.2 33.1 73.4 90 90.3 90 and for the mutant 160.4 32.3
107.0 90 125.7 90. As a result the mutant structure has four
molecules in the asymmetric unit while the native had two. When we run
molecular replacement all programs (CNS, molrep, and amore) find only
two molecules. Phaser finds four but when we try to refine the Rfree
does not drop below 0.44 if we use four molecules and 0.53 if we only
use two no matter how well we built the molecule and regardless of any
addition of water molecules (the resolution of the data is 2.1). The
interesting thing is that in the electron density map we can clearly
see density for a substrate analog that was included in the
crystallization media. Do you thing that we have a case of twinning
here ? We have to mention that Tod Yates served did not indicate any
perfect merohedral twinning (partial merohedral twinning for this
space group is not possible).
We would appreciate any comments
Many thanks
Demetres
