Members of this family are HemZ proteins and are involved in the decarboxylation of coproporphyrinogen III in anaerobic heme biosynthesis. The family is related to, but distinct from HemN (Oxygen-independent coproporphyrinogen-III oxidase 1).
Homuth G, Rompf A, Schumann W, Jahn D
Transcriptional control of Bacillus subtilis hemN and hemZ
▸ Abstract
Previous characterization of Bacillus subtilis hemN, encoding a protein involved in oxygen-independent coproporphyrinogen III decarboxylation, indicated the presence of a second hemN-like gene (B. Hippler, G. Homuth, T. Hoffmann, C. Hungerer, W. Schumann, and D. Jahn, J. Bacteriol. 179:7181-7185, 1997). The corresponding hemZ gene was found to be split into the two potential open reading frames yhaV and yhaW by a sequencing error of the genome sequencing project. The hemZ gene, encoding a 501-amino-acid protein with a calculated molecular mass of 57,533 Da, complemented a Salmonella typhimurium hemF hemN double mutant under aerobic and anaerobic growth conditions. A B. subtilis hemZ mutant accumulated coproporphyrinogen III under anaerobic growth conditions. A hemN hemZ double mutant exhibited normal aerobic and anaerobic growth, indicating the presence of a third alternative oxygen-independent enzymatic system for coproporphyrinogen III oxidation. The hemY gene, encoding oxygen-dependent protoporphyrinogen IX oxidase with coproporphyrinogen III oxidase side activity, did not significantly contribute to this newly identified system. Growth behavior of hemY mutants revealed the presence of an oxygen-independent protoporphyrinogen IX oxidase in B. subtilis. A monocistronic hemZ mRNA, starting 31 bp upstream of the translational start codon, was detected. Reporter gene fusions of hemZ and hemN demonstrated a fivefold anaerobic induction of both genes under nitrate ammonifying growth conditions. No anaerobic induction was observed for fermentatively growing B. subtilis. The B. subtilis redox regulatory systems encoded by resDE, fnr, and ywiD were indispensable for the observed transcriptional induction. A redox regulation cascade proceeding from an unknown sensor via resDE, through fnr and ywiD to hemN/hemZ, is suggested for the observed coregulation of heme biosynthesis and the anaerobic respiratory energy metabolism. Finally, only hemZ was found to be fivefold induced by the presence of H(2)O(2), indicating further coregulation of heme biosynthesis with the formation of the tetrapyrrole enzyme catalase.
HemZ is essential for heme biosynthesis in Mycobacterium tuberculosis
▸ Abstract
The complete sequence and subsequent annotation of the Mycobacterium tuberculosis genome has allowed the prediction of many genes and gene functions by homology. HemZ is a predicted ferrochelatase which lies in an apparent operon with two genes involved in mycolic acid biosynthesis, mabA and inhA. We tried to construct hemZ deletion mutants in M. tuberculosis using a two-step recombination strategy, but could only delete the chromosomal copy when we provided a second functional copy on an integrating plasmid. We further confirmed that hemZ is essential under normal culture conditions by demonstrating that the integrated copy of hemZ could not be removed if it was the only wild-type allele in the cell. We were able to obtain hemZ mutants by supplementation with hemin but not with protoporphyrin IX or hemoglobin confirming that this gene does have a role in heme biosynthesis and that M. tuberculosis can transport hemin intracelullarly. The hemin auxotroph required 2 mug/ml hemin for growth and rapid loss of viability occurred after withdrawal of hemin. These data confirm the role of hemZ in heme biosynthesis and indicate that heme is an essential requirement for M. tuberculosis.
