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heme oxygenase found in pathogenic bacteria This subfamily contains bacterial heme oxygenase (HO, EC 1.14.14.18), where HO is part of a pathway for iron acquisition from host heme and heme products. Most of these proteins have yet to be characterized. HO catalyzes the rate limiting step in the degradation of heme to biliverdin in a multi-step reaction. HO is essential for recycling of iron from heme which is used as a substrate and cofactor for its own degradation to biliverdin, iron, and carbon monoxide. This family includes heme oxygenase (pa-HO) from Pseudomonas aeruginosa, an opportunistic pathogen that causes a variety of systemic infections, particularly in those afflicted with cystic fibrosis, as well as cancer and AIDS patients who are immunosuppressed. Pa-HO, expressed by the PigA gene, is critical for the acquisition of host iron since there is essentially no free iron in mammals, and is unusual since it hydroxylates heme predominantly at the delta-meso heme carbon, while all other well-studied HOs hydroxylate the alpha-meso carbon. Also included in this family is Neisseria meningitidis HO which is substantially different from the human HO, with the reaction product being ferric biliverdin IXalpha rather than reduced iron and free biliverdin IXalpha. HO shares tertiary structure similarity to methane monooxygenase (EC 1.14.13.25), ribonucleotide reductase (EC 1.17.4.1) and thiaminase II (EC 3.5.99.2), but shares little sequence homology. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",