Enhanced polymerization of recombinant human deoxyhemoglobin. beta. 6 Glu yields Ile
- National de la Sante et de la Recherche Medicale (France)
- Faculte des Sciences II, Geneva (Switzerland)
Polymerization of the deoxy form of sickle cell hemoglobin involves both hydrophobic and electrostatic intermolecular contacts. These interactions drive the mutated molecules into long fibrous rods composed of seven pairs of strands. X-ray crystallography of Hb S and electron microscopy image reconstruction of the fibers have revealed the remarkable complementarity between one of the {beta}6 valines of each molecule (the donor site) and an acceptor site at the EF corner of a neighboring tetramer. To estimate the relative importance of this key hydrophobic contact in polymer formation the authors have generated a polymerizing Hb with isoleucine at the {beta}6 position ({beta}E6I) by site-directed mutagenesis. The mutated {beta} chains were produced in Escherichia coli and reassembled into functional tetramers with native {alpha} chains. Compared to native Hb S, the {beta}E6I mutant polymerizes faster and with a shortened delay time in 1.8 M phosphate buffer, indicating an increased stability of the nuclei preceding fiber growth. Computer modeling of the donor-acceptor interaction shows that the presence of an isoleucine side chain at the donor site induced increased contacts with the receptor site and an increased buried surface area, in agreement with the higher hydrophobicity of the isoleucine residue. The agreement between the predicted and experimental differences in solubility suggests that the transfer of the {beta}6 valine or isoleucine side chain from water to a hydrophobic environment is sufficient to explain the observations.
- OSTI ID:
- 6215525
- Journal Information:
- Proceedings of the National Academy of Sciences of the United States of America; (USA), Vol. 87:5; ISSN 0027-8424
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HEMOGLOBIN
PROTEIN ENGINEERING
STRUCTURE-ACTIVITY RELATIONSHIPS
BIOCHEMICAL REACTION KINETICS
CRYSTALLOGRAPHY
ESCHERICHIA COLI
GLUTAMIC ACID
LEUCINE
LIGANDS
X-RAY DIFFRACTION
AMINO ACIDS
BACTERIA
CARBOXYLIC ACIDS
COHERENT SCATTERING
DIFFRACTION
GLOBINS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
MICROORGANISMS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PIGMENTS
PORPHYRINS
PROTEINS
REACTION KINETICS
SCATTERING
550201* - Biochemistry- Tracer Techniques