While building our crystal structure model we encountered density which
we weren't able to assign. The unknown molecule/molecules seems to
coordinate a Ni^2+ -ion. This ion is also coordinated by a histidin and
probably one H_2 O-molecule. The crystals have been grown from a
protein-complex including the carotinoid peridinin, the lipid DGDG and
Chlorophyll. Besides this the solution in which they have been grown
contains Tris pH 8.5, NiCl_2 and PEG 2000 MME.
The linked images show a rotation around the density in 90°-steps (1.1A,
1.2sigma contour level). The above mentioned H_2 O-molecule has been
removed. It is supposed to fill the density that is below the Ni^2+ -Ion
in the first picture.
Images: http://www.bioxtal.rub.de/myst.html.en
Any hints are welcome =)
Mario
