[buster-discuss] Refine occupancy on two different polypeptide chains
vonrhein at globalphasing.com
Mon Jan 29 09:48:57 CET 2018
On Fri, Jan 26, 2018 at 10:17:01AM +0100, Anna Suarez Larsson wrote:
> I am dealing with a pentameric structure composed of two different
> short (80 aa) polypeptide chains, A and B, that are 40%
> identical. In the crystal packing it looks to be no preferred
> orientation for the ring with respect to the two different
> proteins. I would like to combine the two chains in the same
> structure and refine with Buster to get the relative occupancy.
Yes, that should be doable.
> We know from gel electrophoresis of the two proteins coexpressed
> that the relation is 3:2 (A to B) between them, both in crystals and
> in solution. The crystals diffract to about 2.0 � resolution but the
> spots are streaky. The R-values when refining with only one of the
> polypeptide chains are much lower for A compared to B.
> My attempt to do the refinement in Buster using first pdb2occ and then run with the command -Gelly failed with the comment:
> Interpreting CONSTANT and FREE cards:
> =====NOTE BUSTER_CONSTANT OCC FixOcc
> *** ERROR found in interpreting atom specifier from CONSTANT card
> *** ERROR specifier=FixOcc
> *** ERROR does not match any atoms
> *** ERROR *** found processing constant cards
> *** ERROR *** (on call to GELLY_PROCESS_CONSTANT_CARDS_OWN
> *** ERROR *** by s/r GELLY_PROCESS_CONST_COMBINE_CARDS_OWN)
Yes: we never anticipated that the complete model consists of atoms
that will get their occupancy refined - so the FixOcc set/group is
> How should I do to be able to proceed?
What happens if you remove that line (NOTE BUSTER_CONSTANT OCC FixOcc)
from your Gelly file?
> Is it possible to refine double occupancy on all the five
> polypeptide chains or is it required that I keep some of them with
> fixed occupancy?
You should be able to do that, although using pdb2occ might not be the
most elegant way: this tool is mainly intended to handle occupancy
refinement situations with some small(ish) localised items (alternate
conformation side-chains, partially occupied ligands, alternate loop
Please let us know if you hit another issue.
Clemens & Andrew (for buster-develop)
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