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Structures of deoxy and oxy hemerythrin at 2.0 A resolution.
M A Holmes1, I Le Trong, S Turley
1Department of Biological Structure, University of Washington, Seattle 98195.
Journal of Molecular Biology
|April 5, 1991
Summary
Detailed crystallographic analysis of deoxy and oxy hemerythrin reveals structural insights into oxygen binding. The study clarifies the protonation state of the bridging oxygen and the mechanism of dioxygen binding to iron.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Crystallography
Background:
- Hemerythrin is an oxygen-binding protein crucial for respiration in certain invertebrates.
- Previous low-resolution studies provided limited structural detail on its physiological forms.
- Understanding hemerythrin's structure is key to elucidating its oxygen transport mechanism.
Purpose of the Study:
- To determine the high-resolution crystallographic structure of deoxy and oxy hemerythrin.
- To elucidate the structural basis of oxygen binding and release in hemerythrin.
- To refine the understanding of the binuclear iron center's role in oxygen transport.
Main Methods:
- X-ray crystallography at 2.0 A resolution.
- Restrained least-squares refinement of molecular models.
- Analysis of crystallographic data including R-values and reflection data.
Main Results:
- High-resolution structures of deoxy and oxy hemerythrin were obtained with R-values of 16.8% and 17.3%, respectively.
- The protein structure is highly similar to myohemerythrin and met forms.
- The binuclear iron complex retains a bridging oxygen atom, which is protonated (hydroxyl) in deoxy hemerythrin.
Conclusions:
- The structure supports a mechanism where dioxygen binds to deoxy hemerythrin, with proton transfer from the bridge to dioxygen.
- This proton transfer stabilizes the bound dioxygen in a peroxo state via hydrogen bonding.
- The findings provide detailed insights into the molecular mechanism of oxygen binding in hemerythrin.