[phenixbb] low-resolution refinement
jenn.a.weinreich at gmail.com
Fri Jun 10 17:43:04 PDT 2011
I am refining a low-resolution structure of a protein complex (4.4 Å).
The structure was solved by molecular replacement using structures of
individual subunits as search models. Here are some of the questions that I
have (and also points raised by our reviewers.) Your thoughts and
suggestions on how to proceed with this will be very much appreciated.
1) The B factors are very high (300-400). The Wilson B calculated by
phenix.xtriage is ~200. Is this something I should be concerned about?
2) What is the expected (or 'acceptable') gap between R and Rfree at this
resolution. (Current R = 27%, Rfree = 33%) Does this sound reasonable?
3) It has been suggested to me that I should try adding riding hydrogens
during the last round of refinement (to help with geometry). Is this
something I should do?
And if so, should I remove them when I deposit the file to the PDB.
(Hydrogens at 4.5A are probably going to raise a lot of eyebrows...
4) What is the 'acceptable' coordinate and phase errors for structures at
this resolution. (They are now 1.4Å and 36˚)
5) I have been using secondary structure restraints during the refinement,
which seems to work reasonably well. I also tried refinement using
reference model (the structure of the individual components). But refining
with reference models seems to result in high RMSD bonds/angles. Is there
something I'm missing?
Short of growing better crystals, are there other strategies I should be
trying with the existing data?
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the phenixbb