Hemoglobin tetramers stabilized by a single intramolecular cross-link

Area of Science:

• Biochemistry
• Protein Chemistry
• Biophysical Chemistry

Background:

• Hemoglobin (Hb) is crucial for oxygen transport.
• Chemical modifications can alter Hb function and stability.
• Understanding Hb structure-function relationships is key for therapeutic applications.

Purpose of the Study:

• To introduce a specific intramolecular cross-link into bovine and human hemoglobin.
• To investigate the effects of this cross-link on Hb's biochemical and biophysical properties.
• To evaluate the potential of cross-linked Hb for blood substitute development.

Main Methods:

• Reaction of deoxyhemoglobin with bispyridoxal tetraphosphate (bisPL)P4 followed by NaBH4 reduction.
• Characterization of cross-linked hemoglobin using biochemical and biophysical assays.
• Analysis of oxygen affinity, Bohr effect, cooperativity, and stability.

Main Results:

• High yield (80%) of cross-linked hemoglobin achieved using 1 mol (bisPL)P4 per mol Hb.
• Cross-link specifically connects N-terminal residues to lysine on opposite beta chains.
• Reduced oxygen affinity (5-fold in human, 4-fold in bovine) and Bohr effect.
• Increased resistance to heat denaturation and 10-fold greater beta-heme link stability.
• Maintained cooperative oxygen binding with decreased Hill coefficient.

Conclusions:

• Intramolecular cross-linking of hemoglobin with bisPLP4 is an effective method to enhance stability.
• The modification significantly alters oxygen transport characteristics.
• Cross-linked hemoglobin demonstrates promise as a basis for artificial blood substitutes.