A cooperative oxygen-binding hemoglobin from Mycobacterium tuberculosis.

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Two hemoglobin genes, glbN and glbO, were identified in Mycobacterium tuberculosis H37Rv.
• Hemoglobins play crucial roles in oxygen transport and storage in various organisms.

Purpose of the Study:

• To characterize the function and physiological role of the glbN gene product, hemoglobin N (HbN).
• To investigate the oxygen-binding properties and potential protective mechanisms of HbN.

Main Methods:

• Gene expression analysis in Mycobacterium bovis bacillus Calmette-Guérin.
• Ligand binding kinetics and resonance Raman spectroscopy.
• Site-directed mutagenesis studies.

Main Results:

• The glbN gene encodes a dimeric hemoglobin (HbN) with exceptionally high oxygen affinity.
• Oxygen binding is cooperative, characterized by rapid association and slow dissociation rates.
• A unique tyrosine conformation at the B10 position stabilizes bound oxygen.
• HbN expression increases in stationary phase aerobic cultures, not under hypoxia.
• HbN may protect against reactive nitrogen species.

Conclusions:

• HbN exhibits unique structural and functional properties for high-affinity oxygen binding.
• The expression pattern suggests a role beyond simple oxygen transport.
• HbN is likely involved in protecting Mycobacterium tuberculosis from host-induced oxidative stress, particularly reactive nitrogen species.