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Published on: July 31, 2010
Determinants of Ascaris hemoglobin octamer formation
1Howard Hughes Medical Institute, Departments of Molecular Microbiology and Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
The Journal of Biological Chemistry
|November 26, 1998
Summary
The Ascaris hemoglobin tail aids octamer assembly, not stabilization. This charged tail acts as an intramolecular chaperone, crucial for forming the functional hemoglobin structure.
Area of Science:
- Biochemistry
- Structural Biology
- Parasitology
Background:
- Ascaris hemoglobin (AH) is an oxygen-avid homooctamer with a unique structure.
- It features two globin folds and a charged COOH-terminal tail with four His-Lys-Glu-Glu (HKEE) repeats.
Purpose of the Study:
- To investigate the role of the AH tail in octamer formation and stability.
- To compare the tail function with that of Pseudoterranova decipiens hemoglobin (PH).
Main Methods:
- Deletion analysis of the AH tail.
- Interchanging tails between AH and PH.
- Dissociation analysis of wild-type and mutant hemoglobins.
- Mutational and biochemical studies.
Main Results:
- At least two HKEE repeats are necessary for efficient AH octamer formation.
- The first four tail residues alone moderately promote multimerization.
- The PH tail also moderately promotes octamer formation.
- Octamer stability is primarily due to globin fold interactions, not the tail.
- Isoleucine 15 in the AB loop is critical for stabilizing interactions.
Conclusions:
- The AH tail functions as an intramolecular chaperone, facilitating octamer assembly.
- The tail does not stabilize the pre-formed quaternary structure.
- Globin fold interactions, particularly involving isoleucine 15, stabilize the assembled octamer.
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