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Title
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Atomic resolution structure of obelin: soaking with calcium enhances electron density of the second oxygen atom substituted at the C2-position of coelenterazine.
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Authors
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Z.J.Liu,
E.S.Vysotski,
L.Deng,
J.Lee,
J.Rose,
B.C.Wang.
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Ref.
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Biochem Biophys Res Commun, 2003,
311,
433-439.
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PubMed id
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Abstract
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The spatial structure of the Ca(2+)-regulated photoprotein obelin has been
solved to resolution of 1.1A. Two oxygen atoms are revealed substituted at the
C2-position of the coelenterazine in contrast to the obelin structure at 1.73A
resolution where one oxygen atom only was disclosed. The electron density of the
second oxygen atom was very weak but after exposing the crystals to a trace of
Ca(2+), the electron densities of both oxygen atoms became equally intense. In
addition, one Ca(2+) was found bound in the loop of the first EF-hand motif.
Four of the ligands were provided by protein residues Asp30, Asn32, Asn34, and
the main chain oxygen of Lys36. The other two were from water molecules. From a
comparison of B-factors for the residues constituting the active site, it is
suggested that the variable electron densities observed in various photoprotein
structures could be attributed to different mobilities of the peroxy oxygen
atoms.
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