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pH-dependent structural changes in haemoglobin component V from the midge larva Propsilocerus akamusi (Orthocladiinae, Diptera)

pH-dependent structural changes in haemoglobin component V from the midge larva Propsilocerus... 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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Crystallographica Section D: Biological Crystallography International Union of Crystallography

pH-dependent structural changes in haemoglobin component V from the midge larva Propsilocerus akamusi (Orthocladiinae, Diptera)

pH-dependent structural changes in haemoglobin component V from the midge larva Propsilocerus akamusi (Orthocladiinae, Diptera)

Acta Crystallographica Section D: Biological Crystallography , Volume 66 (3): 258 – Feb 12, 2010

Abstract

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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References (55)

Publisher
International Union of Crystallography
Copyright
Copyright (c) 2010 International Union of Crystallography
Subject
insect haemoglobin, pH-dependence, swinging movement
ISSN
0907-4449
eISSN
1399-0047
DOI
10.1107/S0907444909055760
pmid
20179337
Publisher site
See Article on Publisher Site

Abstract

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.

Journal

Acta Crystallographica Section D: Biological CrystallographyInternational Union of Crystallography

Published: Feb 12, 2010

Keywords: insect haemoglobin ; pH-dependence ; swinging movement .

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