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PDBsum entry 3a9m
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Oxygen transport
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PDB id
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3a9m
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References listed in PDB file
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Key reference
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Title
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Ph-Dependent structural changes in haemoglobin component V from the midge larva propsilocerus akamusi (orthocladiinae, Diptera).
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Authors
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T.Kuwada,
T.Hasegawa,
T.Takagi,
I.Sato,
F.Shishikura.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2010,
66,
258-267.
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PubMed id
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Abstract
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Haemoglobin component V (Hb V) from the midge larva Propsilocerus akamusi
exhibits oxygen affinity despite the replacement of HisE7 and a pH-dependence of
its functional properties. In order to understand the contribution of the distal
residue to the ligand-binding properties and the pH-dependent structural changes
in this insect Hb, the crystal structure of Hb V was determined under five
different pH conditions. Structural comparisons of these Hb structures indicated
that at neutral pH ArgE10 contributes to the stabilization of the haem-bound
ligand molecule as a functional substitute for the nonpolar E7 residue. However,
ArgE10 does not contribute to stabilization at acidic and alkaline pH because of
the swinging movement of the Arg side chain under these conditions. This
pH-dependent behaviour of Arg results in significant differences in the
hydrogen-bond network on the distal side of the haem in the Hb V structures at
different pH values. Furthermore, the change in pH results in a partial movement
of the F helix, considering that coupled movements of ArgE10 and the F helix
determine the haem location at each pH. These results suggested that Hb V
retains its functional properties by adapting to the structural changes caused
by amino-acid replacements.
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