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. Author manuscript; available in PMC: 2020 Dec 1.
Published in final edited form as: Curr Opin Struct Biol. 2019 Feb 22;59:19–28. doi: 10.1016/j.sbi.2019.01.006

Figure 8. Multiple enzymes, multiple binding modes, multiple ways to degrade heme.

Figure 8.

Canonical heme oxygenase enzymes HO1 and HemO ((a); PDBID: 1N45 and (b); PDBID: 1SK7), respectively) bind heme in a planar orientation. HO1 stereospecifically produces α-biliverdin, while HemO produces β- and γ-biliverdin due to the ~100° rotation of the heme ring in this active site relative to HO1. IsdG-like heme oxygenase enzymes IsdG/I and MhuD ((c); PDBID: 2ZDO and (d); PDBID: 4NL5, respectively) “ruffle” the heme porphyrin which results in cleavage of meso-carbons and products that are different than canonical HO’s (see figure 7).The heme ring in MhuD is rotated ~90° relative to the heme in IsdG/I, also contributing to the different bilin products that are produced.