Hi all,
I recently solved a structure using SAD or SIRAS successfully (refinement using
native data). But I came across some questions about the heave atom (Hg) sites.
SG : P212121. Cell: 61.000 137.700 142.170 90.00 90.00 90.00 (native and
derivative are very similar).
1. I used shelxD finding the Hg sites, but got different results from SAD and
SIRAS. Here paste the first 3 sites:
X Y Z X Y
Z
(fractional) (orthogonal)
SAD:
Hg1 0.598389 0.567345 0.098041 36.759 78.146 13.983
Hg2 0.901955 0.570168 -0.098881 55.407 78.535 -14.102
Hg3 0.727585 0.594368 -0.240330 44.696 81.868 -34.276
SIRAS:
Hg1 0.598717 0.432159 0.098363 36.522 59.508 13.984
Hg2 0.901527 0.430199 -0.098437 54.993 59.238 -13.995
Hg3 0.727432 0.406845 -0.240253 44.373 56.023 -34.157
It seems there is a symmetry plane m(x,1/2,z) between SAD sites and SIRAS
sites. The above HA coordinates were in real space not the partterson space,
right? So could someone tell me why there is a m?
PS: the Harker section plots (FFT for patterson in CCP4) of difference
patterson and ano-difference patterson are very similar.
2. I put the Hg sites caculated by shelxD (say, the SAD sites) to SHARP and got
the density map (looks very good). RESOLVE was used to autobuild the model.
The Fo-Fc map (Fo from Hg-data, Fc from the model after refinement) at sig>5
obviously showed the Hg sites (around Cys). But the heave atom coordinates
(from shelxD or sharp) didn't match the Fo-Fc density. I don't know why is
that? Dose it bucause the coordinate system mismatch?
Any help would be much appreciated.
Thanks,
Pu
