title: The hmuQ and hmuD genes from Bradyrhizobium japonicum encode heme-degrading enzymes.
abstract: Utilization of heme by bacteria as a nutritional iron source involves the transport of exogenous heme, followed by cleavage of the heme macrocycle to release iron. Bradyrhizobium japonicum can use heme as an iron source, but no heme-degrading oxygenase has been described. Here, bioinformatics analyses of the B. japonicum genome identified two paralogous genes renamed hmuQ (bll7075) and hmuD (bll7423) that encode proteins with weak similarity to the heme-degrading monooxygenase IsdG from Staphylococcus aureus. The hmuQ gene is clustered with known heme transport genes in the genome. Recombinant HmuQ bound heme with a K(d) value of 0.8 microM and showed spectral properties consistent with a heme oxygenase. In the presence of a reductant, HmuQ catalyzed the degradation of heme and the formation of biliverdin. The hmuQ and hmuD genes complemented a Corynebacterium ulcerans heme oxygenase mutant in trans for utilization of heme as the sole iron source for growth. Furthermore, homologs of hmuQ and hmuD were identified in many bacterial genera, and the recombinant homolog from Brucella melitensis bound heme and catalyzed its degradation. The findings show that hmuQ and hmuD encode heme oxygenases and indicate that the IsdG family of heme-degrading monooxygenases is not restricted to gram-positive pathogenic bacteria.
authors.affiliation: Department of Biochemistry, 140 Farber Hall, State University of New York at Buffalo, Buffalo, NY 14214, USA.
authors.forename: Sumant
authors.initials: S
authors.lastname: Puri
authors.forename: Mark R
authors.initials: MR
authors.lastname: O'Brian
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001664:Biliverdine / Q000378:metabolism; D020369:Bradyrhizobium / Q000201:enzymology* / Q000235:genetics; D017347:Brucella melitensis / Q000201:enzymology / Q000235:genetics; D019295:Computational Biology; D003352:Corynebacterium / Q000235:genetics; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D016680:Genome, Bacterial / Q000235:genetics; D006418:Heme / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013057:Spectrum Analysis; D013211:Staphylococcus aureus / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D011994:Recombinant Proteins; D006418:Heme; D006899:Mixed Function Oxygenases; D001664:Biliverdine