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Structural factors governing hemin dissociation from metmyoglobin
M S Hargrove1, A J Wilkinson, J S Olson
1Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251-1892, USA.
Biochemistry
|September 3, 1996
Summary
Amino acid mutations in metmyoglobin reveal key residues stabilizing the heme group. His93 and Leu89 are critical for preventing hemin loss, highlighting the importance of specific interactions for protein structure.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Science
Background:
- Metmyoglobin's function relies on its prosthetic heme group.
- Understanding heme binding is crucial for protein stability and function.
Purpose of the Study:
- To identify amino acid residues critical for retaining the heme prosthetic group in metmyoglobin.
- To elucidate the structural factors stabilizing heme binding.
Main Methods:
- Generated approximately 100 metmyoglobin mutants.
- Measured rates of hemin dissociation from these mutants at different pH levels.
Main Results:
- Mutations of His93(F8) and Leu89(F4) significantly increased hemin loss (>100-fold).
- Several other contact and noncontact residues also influenced hemin dissociation rates (>10-fold).
- Hydrophobic interactions, His93 covalent bond, and distal residue hydrogen bonding are key stabilizing factors.
Conclusions:
- Specific amino acid residues, particularly His93 and Leu89, are vital for maintaining heme group stability in metmyoglobin.
- Hydrophobic interactions and direct covalent/hydrogen bonds play a more significant role than surface electrostatic interactions.