Fabien,
The extra density may be from a his-tag or cloning artifacts left over
at the beginning or end of your protein sequence. You may be seeing the
residues coming from a neighboring molecule. I have seen parts of a
C-terminal his-tag ordered in the electron density before.
Jon Schuermann
--
Jonathan P. Schuermann, Ph. D.
Beamline Scientist
NE-CAT, Building 436E
Advanced Photon Source (APS)
Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439
email: [email protected]
Tel: (630) 252-0682
Fax: (630) 252-0687
Fabien Bergeret wrote:
Hello
We’re resolving a structure of a soluble protein and in the electronic
density map (maximum resolution at 2.2Å), we observe a supplementary
density that does not belong to the protein. This density is present
in two different crystalline forms obtained in different
crystallization conditions.
This density could be represented by an oligopeptide ~10 residues long
for which there is no ambiguity about its polarity. Furthermore, side
chains are quite easily visible and a sequence can therefore be assigned.
The deduced sequence doesn’t belong to the sequence of the protein of
interest, meaning that the oligopeptide has been co-purified and
co-crystallized.
Has somebody met a similar situation? Could you please give us some
advices in terms of refinement, validation, etc.?
Thanks in advance
Best regards
Fabien
PhD student
[email protected] <mailto:[email protected]>
--
Jonathan P. Schuermann, Ph. D.
Beamline Scientist
NE-CAT, Building 436E
Advanced Photon Source (APS)
Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439
email: [email protected]
Tel: (630) 252-0682
Fax: (630) 252-0687
