title: Identification of Escherichia coli HemG as a novel, menadione-dependent flavodoxin with protoporphyrinogen oxidase activity.
abstract: Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) catalyzes the six-electron oxidation of protoporphyrinogen IX to the fully conjugated protoporphyrin IX. Eukaryotes and Gram-positive bacteria possess an oxygen-dependent, FAD-containing enzyme for this step, while the majority of Gram-negative bacteria lack this oxygen-dependent PPO. In Escherichia coli, PPO activity is known to be linked to respiration and the quinone pool. In E. coli SASX38, the knockout of hemG causes a loss of measurable PPO activity. HemG is a small soluble protein typical of long chain flavodoxins. Herein, purified recombinant HemG was shown to be capable of a menadione-dependent conversion of protoporphyrinogen IX to protoporphyrin IX. Electrochemical analysis of HemG revealed similarities to other flavodoxins. Interestingly, HemG, a member of a class of the long chain flavodoxin family that is unique to the gamma-proteobacteria, possesses a 22-residue sequence that, when transferred into E. coli flavodoxin A, produces a chimera that will complement an E. coli hemG mutant, indicating that this region confers PPO activity to the flavodoxin. These findings reveal a previously unidentified class of PPO enzymes that do not utilize oxygen as an electron acceptor, thereby allowing gamma-proteobacteria to synthesize heme in both aerobic and anaerobic environments.
authors: Biomedical and Health Sciences Institute and Department of Microbiology, University of Georgia, Athens, Georgia 30602, USA.
authors: Tye O
authors: TO
authors: Boynton
authors: Lauren E
authors: LE
authors: Daugherty
authors: Tamara A
authors: TA
authors: Dailey
authors: Harry A
authors: HA
authors: Dailey
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D010957:Plasmids; D050768:Protoporphyrinogen Oxidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D024483:Vitamin K 3 / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D011994:Recombinant Proteins; D024483:Vitamin K 3; C493977:HemG protein, E coli; D050768:Protoporphyrinogen Oxidase