Dear colleagues,
we have collected 200 degrees worth of oscillation data on a
selenomethionine derivative (1 "non-terminal" methionyl per 120 residues)
to 2A resolution.
XDS provides the following output:
<COLLECT.LP>
LATTICE- BRAVAIS- QUALITY UNIT CELL CONSTANTS (ANGSTROEM & DEGREES)
CHARACTER LATTICE OF FIT a b c alpha beta gamma
* 44 aP 0.0 47.9 47.9 171.2 90.1 90.0 119.9
* 31 aP 0.4 47.9 47.9 171.2 89.9 90.0 60.1
* 39 mC 0.8 83.0 47.9 171.2 90.0 90.1 89.9
* 14 mC 2.2 47.9 82.9 171.2 90.0 90.1 90.0
* 34 mP 2.3 47.9 171.2 47.9 90.1 119.9 90.0
* 29 mC 2.6 47.9 82.9 171.2 90.0 90.1 90.0
* 38 oC 2.8 47.9 83.0 171.2 89.9 90.0 90.1
* 10 mC 2.8 83.0 47.9 171.2 90.0 90.1 89.9
* 13 oC 2.9 47.9 82.9 171.2 90.0 90.1 90.0
* 12 hP 3.4 47.9 47.9 171.2 90.1 90.0 119.9
35 mP 249.9 47.9 47.9 171.2 90.0 90.1 119.9
33 mP 250.4 47.9 47.9 171.2 90.0 90.1 119.9
32 oP 251.8 47.9 47.9 171.2 90.1 90.0 119.9
.
.
.
SPACE-GROUP UNIT CELL CONSTANTS UNIQUE Rmeas
COMPARED LATTICE-
NUMBER a b c alpha beta gamma
CHARACTER
5 82.9 48.0 171.3 90.0 90.0 90.0 13033 15.3 36401
10 mC
143 47.9 47.9 171.3 90.0 90.0 120.0 8371 17.4 41063
12 hP
149 47.9 47.9 171.3 90.0 90.0 120.0 4496 17.0 44938
12 hP
150 47.9 47.9 171.3 90.0 90.0 120.0 4720 16.8 44714
12 hP
168 47.9 47.9 171.3 90.0 90.0 120.0 4255 16.9 45179
12 hP
* 177 47.9 47.9 171.3 90.0 90.0 120.0 2549 16.7 46885
12 hP
21 48.0 82.9 171.3 90.0 90.0 90.0 6758 15.1 42676
13 oC
5 48.0 82.9 171.3 90.0 90.1 90.0 12751 15.8 36683
14 mC
5 48.0 82.9 171.3 90.0 90.1 90.0 12751 15.8 36683
29 mC
1 47.9 47.9 171.3 89.9 90.0 60.1 24755 9.4 24679
31 aP
21 47.9 83.0 171.3 90.0 90.0 90.0 6765 9.2 42669
38 oC
3 47.9 171.3 47.9 90.0 119.9 90.0 12671 9.6 36763
34 mP
5 83.0 47.9 171.3 90.0 90.1 90.0 13029 8.9 36405
39 mC
1 47.9 47.9 171.3 90.1 90.0 119.9 24755 9.4 24679
44 aP
</COLLECT.LP>
We scaled reflections, with reasonable residuals, assuming space group P622
and have a reasonable solution in P6122. Refinement does not take us past
an Rfree of aprrox. 0.4. The apparent quality of the model-phased map
varies across the asymmetric unit.
The L-test does not indicate merohedral twinning. Translational
pseudosymmetry was not detected. <Merohedral> twinning has been tentatively
ruled out.
Before considering Order-Disorder-type crystal defects (as reviewed by
Andrey Lebedev here: http://www.ysbl.york.ac.uk/mxstat/andrey/ecm2010.pdf),
we would like to rule out that we might have erroneously applied too many
symmetry constraints. To that end, we have scaled data in C2. We observed
anomalous difference fourier peaks corresponding to positions of 6 selenium
atoms in the current model, but refinement still does not proceed, and maps
look similar to P6122 treatment. To "cover all bases" we would like to
extend the asymmetric unit to P1. And here is the question:
Does it suffice to pursue any one of the P1-associated lattices in the XDS
table or do both need to be tested?
Many thanks as always,
Wolfram Tempel
