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Structural features of the protoporphyrin-apomyoglobin complex: a proton NMR spectroscopy study
1Department of Chemistry, Pennsylvania State University, University Park 16802.
Biochemistry
|December 18, 1990
Summary
The binding of protoporphyrin IX to apomyoglobin helps restore the native structure of myoglobin. This study reveals how iron-free myoglobin interactions organize the heme binding site and protein fold.
Area of Science:
- Biochemistry
- Structural Biology
- Protein NMR Spectroscopy
Background:
- Myoglobin's native structure and heme binding site geometry are influenced by iron-histidine coordination.
- Apomyoglobin, lacking iron, provides a model to study these influences.
Purpose of the Study:
- To investigate the structural properties of the apomyoglobin-protoporphyrin IX complex.
- To determine the effect of iron-to-histidine coordination on the native myoglobin fold.
- To analyze the heme binding site geometry in the absence of iron.
Main Methods:
- Standard two-dimensional proton nuclear magnetic resonance (2D 1H NMR) spectroscopy.
- Nuclear Overhauser spectroscopy (NOE) for resonance assignment.
Main Results:
- A spectral resemblance was observed between carbonmonoxymyoglobin and des-iron myoglobin.
- Protoporphyrin IX binds in the same orientation as heme.
- Most residues interacting with the prosthetic group adopted a holomyoglobin conformation.
- Tertiary structure features near protein termini were characterized.
Conclusions:
- Apomyoglobin-protoporphyrin IX interactions can organize the heme binding site.
- These interactions also organize unfolded regions of the apoprotein into the native holoprotein structure.