title: HmuS and HmuQ of Ensifer/Sinorhizobium meliloti degrade heme in vitro and participate in heme metabolism in vivo.
abstract: Ensifer meliloti is a nitrogen-fixing symbiont of the alfalfa legume able to use heme as an iron source. The transport mechanism involved in heme acquisition in E. meliloti has been identified and characterized, but the fate of heme once inside the cell is not known. In silico analysis of E. meliloti 1021 genome revealed no canonical heme oxygenases although two genes encoding putative heme degrading enzymes, smc01518 and hmuS, were identified. SMc01518 is similar to HmuQ of Bradyrhizobium japonicum, which is weakly homologous to the Staphylococcus aureus IsdG heme-degrading monooxygenase, whereas HmuS is homolog to Pseudomonas aeruginosa PhuS, a protein reported as a heme chaperone and as a heme degrading enzyme. Recombinant HmuQ and HmuS were able to bind hemin with a 1:1 stoichiometry and displayed a Kd value of 5 and 4 µM, respectively. HmuS degrades heme in vitro to the biliverdin isomers IX-β and IX-δ in an equimolar ratio. The HmuQ recombinant protein degrades heme to biliverdin IX-δ only. Additionally, in this work we demonstrate that humS and hmuQ gene expression is regulated by iron and heme in a RirA dependent manner and that both proteins are involved in heme metabolism in E. meliloti in vivo.
authors.affiliation: Biochemical and Microbial Genomics Department, Instituto de Investigaciones Biológicas Clemente Estable, MEC, Montevideo, Uruguay.
authors.forename: Vanesa
authors.initials: V
authors.lastname: Amarelle
authors.affiliation: Biochemical and Microbial Genomics Department, Instituto de Investigaciones Biológicas Clemente Estable, MEC, Montevideo, Uruguay.
authors.forename: Federico
authors.initials: F
authors.lastname: Rosconi
authors.affiliation: CONICET and Faculty of Pharmacy and Biochemistry, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Lázaro-Martínez
authors.affiliation: CONICET and Faculty of Pharmacy and Biochemistry, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Graciela
authors.initials: G
authors.lastname: Buldain
authors.affiliation: Biochemical and Microbial Genomics Department, Instituto de Investigaciones Biológicas Clemente Estable, MEC, Montevideo, Uruguay.
authors.forename: Francisco
authors.initials: F
authors.lastname: Noya
authors.affiliation: State University of New York at Buffalo, New York, USA.
authors.forename: Mark R
authors.initials: MR
authors.lastname: O'Brian
authors.affiliation: Biochemical and Microbial Genomics Department, Instituto de Investigaciones Biológicas Clemente Estable, MEC, Montevideo, Uruguay. efabiano@iibce.edu.uy.
authors.forename: Elena
authors.initials: E
authors.lastname: Fabiano
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology; D001664:Biliverdine / Q000737:chemistry; D055162:Biocatalysis; D004790:Enzyme Induction; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006427:Hemin / Q000494:pharmacology; D007501:Iron / Q000494:pharmacology; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000737:chemistry* / Q000502:physiology; D016962:Sinorhizobium meliloti / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D006418:Heme; D006427:Hemin; D007501:Iron; D006899:Mixed Function Oxygenases; D001664:Biliverdine
keywords: E. meliloti; Heme; Heme-degradation; Heme-oxygenase; Iron metabolism; Rhizobia