title: Unique coupling of mono- and dioxygenase chemistries in a single active site promotes heme degradation.
abstract: Bacterial pathogens must acquire host iron for survival and colonization. Because free iron is restricted in the host, numerous pathogens have evolved to overcome this limitation by using a family of monooxygenases that mediate the oxidative cleavage of heme into biliverdin, carbon monoxide, and iron. However, the etiological agent of tuberculosis, Mycobacterium tuberculosis, accomplishes this task without generating carbon monoxide, which potentially induces its latent state. Here we show that this unusual heme degradation reaction proceeds through sequential mono- and dioxygenation events within the single active center of MhuD, a mechanism unparalleled in enzyme catalysis. A key intermediate of the MhuD reaction is found to be meso-hydroxyheme, which reacts with O2 at an unusual position to completely suppress its monooxygenation but to allow ring cleavage through dioxygenation. This mechanistic change, possibly due to heavy steric deformation of hydroxyheme, rationally explains the unique heme catabolites of MhuD. Coexistence of mechanistically distinct functions is a previously unidentified strategy to expand the physiological outcome of enzymes, and may be applied to engineer unique biocatalysts.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Aoba, Sendai 980-8577, Japan; matsui@tagen.tohoku.ac.jp mis2@tagen.tohoku.ac.jp.
authors.forename: Toshitaka
authors.initials: T
authors.lastname: Matsui
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Aoba, Sendai 980-8577, Japan;
authors.forename: Shusuke
authors.initials: S
authors.lastname: Nambu
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697; Department of Pharmaceutical Sciences, University of California, Irvine, CA 92697;
authors.forename: Celia W
authors.initials: CW
authors.lastname: Goulding
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Aoba, Sendai 980-8577, Japan;
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takahashi
authors.affiliation: Department of Chemistry, Graduate School of Humanities and Sciences, Nara Women's University, Kitauoyanishi, Nara 630-8506, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fujii
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Aoba, Sendai 980-8577, Japan; matsui@tagen.tohoku.ac.jp mis2@tagen.tohoku.ac.jp.
authors.forename: Masao
authors.initials: M
authors.lastname: Ikeda-Saito
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry*; D002384:Catalysis; D020134:Catalytic Domain; D049308:Dioxygenases / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D007501:Iron / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D014376:Tuberculosis / Q000382:microbiology
chemical_list: D006418:Heme; D002248:Carbon Monoxide; D007501:Iron; D006899:Mixed Function Oxygenases; D049308:Dioxygenases; D006419:Heme Oxygenase (Decyclizing); D010100:Oxygen
keywords: MhuD; Mycobacterium tuberculosis; dioxygenation; heme degradation; monooxygenation