One question - do you have two pairs of molecules, each related by the
PST or is there extra non-crystallographic translation ?
Averaging or NCS restraints dont give much extra information for
molecules in the same orientation.
Certainly any pseudo translation will generate sets of weak and strong
reflections but unless you have a simple fraction in each direction it
is not easy to try to select a sub-set for refinement.
Do all the data sets merge together reasonably?
You probably just have to slog it through - do you have any
experimental phasing at all?
Eleanor
Maruf Ali wrote:
Dear all
I have recently collected several datasets on different crystals of a
particular protein with a resolution range form 2.4 - 3.2A. All
datasets seem to process well in p21 with a unit cell of 109.6
83.1 115.87 90 94.8 90, and this space group is further
supported by analysis with the program pointless. The dataset have
very reasonable statistics and Rmerge values, with no indication of
twinning. Analysis of the self patterson indicated a 43% off origin
peak at 0.3 0.5 0.47. This was further flagged by pointless and
molrep as a Psuedo cell translation (PST). Looking at the systematic
absences there are some unusually strong and weak peaks. Initially
after some toiling with molecular replacement, there was a clear
solution with four molecules in the asymmetric unit. The maps
generated were good enough to build the core of the protein but do not
look like maps generated from data at 2.4A-3.2. Further more the free
R is stuck at around 40%, and there is no difference in free R when I
apply ncs or not or any difference in the maps. After building by hand
and with phenix autobuild there is still no difference in maps and
Rfree. I have read papers where labs have successfully refined PST
data by separating the reflections according to the PST. Oksanen et al
2006 acta D62 1369-1374: Poy et al 2001 NSMB Vol 8 no12 pg 1053:
VajDos et al protein science 1997 6;2297
My specific question are
Firstly how would I deal with refining PST data? (assuming this is the
problem).
Second with off origin peak of 0.3 0.5 0.47 how would I separate the
reflections?
Thirdly any comments would be valued
Thank you in advance
Maruf
Dr Maruf Ali
Section of Structural Biology,
Institute of Cancer Research,
237 Fulham road,
London.
SW3 6JB
The Institute of Cancer Research: Royal Cancer Hospital, a charitable
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