[phenixbb] AutoSol Br SAD/MAD

Ian Slaymaker iscrystallo at gmail.com
Mon Mar 12 12:17:52 PDT 2018

Hello Phenixbb,

I've been out of the crystallography game for a few years and was hoping
for some suggestions.
I'm trying to phase a structure (~1200aa protein:DNA complex) with native
data out to 2.0A and SAD/MAD data out to 3.0-2.6. I'm trying to use Br/I
soaking while I wait for Sel-Met crystals to grow.

I'm collecting 1800 frames at a synchrotron and scaling together multiple
MAD wavelength sets (30 degree inverse wedges) collected from the same
crystal with phenix.scale_and_merge to achieve >85% anomalous data
(determined by xtriage). Anomalous signal of the merged data is around 10
at the 3.5 angstrom shell. I'm keeping an eye on the merging statistics,
but I'm not sure what the critical stats to monitor are.

AutoSol has given me a a few possible solutions, finding between 3 and 8
sites for MAD and SAD sets(I'm letting AutoSol decide how many to find)
with Resolve Rfactors around 0.34, but low map skew (<1 and sometimes
negative). I've tried using the initial sites to search for additional Br
sites, but with no luck, and the density isn't good enough to build
anything into. I'm doing hyss searches with various resolution cutoffs and
continue to get the same/similar uninterpretable density with very few
heavy atom sites found.

My questions:
What are the critical stats to look at when merging data for anomalous
Are there parameters to explore in AutoSol to identify more heavy atom
Should I accept that I need to wait for new crystals to grow or keep
charging ahead with this data, encouraged by some promising numbers by

Thank you in advance for the suggestions.

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