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Structure and function of 6,7-dicarboxyheme-substituted myoglobin
S Neya1, N Funasaki, N Igarashi
1Department of Physical Chemistry, Kyoto Pharmaceutical University, Japan. sneya@mb.kyoto-phu.ac.jp
Biochemistry
|May 16, 1998
Summary
Researchers modified myoglobin with a synthetic heme, altering its structure and function. This modification reduced oxygen affinity and stabilized the heme-protein interaction via a novel salt bridge.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Chemistry
Background:
- Myoglobin's native structure relies on heme propionate-apoglobin linkages.
- Synthetic hemes offer opportunities to probe protein structure-function relationships.
Purpose of the Study:
- To investigate structural and functional changes in myoglobin reconstituted with a compact synthetic heme (6,7-dicarboxy-1,2,3,4,5,8-hexamethylheme).
- To understand the impact of disrupted heme propionate-apoglobin linkages on myoglobin's properties.
Main Methods:
- Reconstitution of myoglobin with a synthetic heme.
- Spectroscopic analysis (oxygen affinity measurements, autoxidation rates).
- X-ray crystallography (1.9 Å resolution) and proton NMR spectroscopy.
Main Results:
- The synthetic heme significantly lowered oxygen affinity (3-fold) and altered autoxidation rates.
- X-ray crystallography revealed a unique heme orientation with carboxylates extending towards the solvent.
- A novel salt bridge formed between the heme's 6-carboxylate and Arg45, stabilizing the heme.
Conclusions:
- The synthetic heme's electron-withdrawing carboxylates reduce oxygen affinity.
- The novel Arg45-heme salt bridge is crucial for heme fixation and stability within the myoglobin pocket.
- Disruption of native linkages can be compensated by engineered interactions for protein stability.