Heme utilization by pathogenic bacteria: not all pathways lead to biliverdin

Area of Science:

• Biochemistry
• Microbiology
• Enzymology

Background:

• Pathogenic bacteria utilize host heme for iron acquisition, essential for survival and virulence.
• Heme oxygenases (HOs) catalyze heme degradation, releasing iron.
• Both eukaryotic and bacterial HOs exist, with canonical enzymes sharing structural and mechanistic similarities.

Purpose of the Study:

• To review the diverse mechanisms of heme degradation in pathogenic bacteria.
• To highlight the discovery of noncanonical heme oxygenases and other heme-degrading factors.
• To discuss the mechanistic differences between enzymatic heme oxygenation and nonenzymatic coupled oxidation.

Main Methods:

• Literature review and synthesis of existing research on heme oxygenases and heme degradation.
• Comparative analysis of canonical and noncanonical heme oxygenases from various bacterial species.
• Discussion of in vitro heme degradation assays and their limitations.

Main Results:

• Identification of structurally and mechanistically distinct noncanonical HOs in bacteria like Staphylococcus aureus and Mycobacterium tuberculosis.
• Discovery of novel heme-degrading factors lacking homology to known HOs.
• Recognition of mechanistic differences between enzymatic heme oxygenation and coupled oxidation, particularly in intermediate stabilization and hydroxylation.

Conclusions:

• Bacterial heme degradation is more diverse than previously understood, involving canonical HOs, noncanonical HOs, and other factors.
• Accurate characterization of heme oxygenase activity requires ensuring successive oxygenation steps and avoiding misinterpretation of coupled oxidation.
• A systems biology approach is recommended for comprehensive characterization of bacterial heme degradation.