[phenixbb] unusual maps and Rfree for 1.75 structure

Yuri yuri.pompeu at ufl.edu
Sat Apr 16 19:50:27 PDT 2011

I am solving a structure of an enzyme that I have solved many times 
before, the only difference is a single mutation in the active site.
The crystal grew in basically exact conditions (macroscopically 
speaking they look different) as the other mutants I had. I scaled the 
data P 43 21 2 Rsym 0.068.  Like all the other data sets I had before.
This time however, the initial model has Rfree of about 0.27 and the 
maps look more like those of a 2.5 - 2.8 structure. My experinence with 
this enzyme is that I should be looking at around 0.22 or lower Rfree, 
and pretty clear maps as I saw for my 1.9 structure. Xtriage does not 
detect any pathologies.
I rececked my scaling log file, and it lists the systematic absences 
for the data.
I see some that are not that "weak"
for instance :
h k l      I/sigma
0 0 1        6.0
0 0 2        5.8
0 0 13       7.8

So I am inclined to reprocess my data in P 4 2 2. Are these "symptoms" 
of a possible wrong space group assignment? Is there something else 
obvious I am overlooking?
Thank you

Yuri Pompeu

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