[phenixbb] TaBr SAD Autosol and Phaser

Ian S iscrystallo at gmail.com
Wed Apr 4 16:22:07 PDT 2018

Hi Phenixbb,

I trying to phase a structure soaked in TaBr and am running into some
technical problems. My anomalous signal goes out to about 4.5 and I have a
1.9A native data set. SIR hasn't worked so far.

Autosol SAD has given me several convincing solutions when searching for
Tantalum (not TX), finding 11 sites (not clustered) at 6 angstroms: FOM
=0.478, map=0.1.3, and corr of 0.82 and a final score of 37+-15.71. By only
playing around with the sites I can get an overall score of 73 +- 4.58, map
skew to 0.5, and a RMS density to 0.79, thought the R-factor increases to
.43 and the FOM .

Perhaps not suprisingly at this resolution, the map is uninterpretable
(maybe some helices) so I'm trying to improve the phases by model building
and by using Phaser and giving it TX sites.
If I put the Ta sites in Phaser with the same dataset as Autosol, I get a
FOM of .342. If I use the TX label it drops to 0.143. What is happening
here? I know that typically TaBr has one or two major sites (my protein
isnt massive, only about 1200 aa predicted in the ASU) , so I use only the
top two major sites and have the same problem. Does this indicate that the
Ta sites Autosol found are not in fact the sites I'm looking for? Or maybe
that there really are 10 TaBr sites all with low occupancy? Any suggestions
would be appreciated.
Thank you.

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