Crystal structure of Campylobacter jejuni ChuZ: a split-barrel family heme oxygenase with a novel heme-binding mode

The heme oxygenase ChuZ is part of the iron acquisition mechanism of Campylobacter jejuni, a major pathogen causing enteritis in humans. ChuZ is required for C. jejuni to use heme as the sole iron source. The crystal structure of ChuZ was resolved at 2.5Å, and it was revealed to be a homodimer with a split-barrel fold. One heme-binding site was at the dimer interface and another novel heme-binding site was found on the protein surface. Heme was bound in this site by four histidine side-chains through hydrophobic interactions. Based on stoichiometry studies and comparisons with other proteins, the possibility that similar heme-binding site exists in homologous proteins and its possible functions are discussed. The structural and mutagenesis analyses reported here establish ChuZ and ChuZ homologs as a new bacterial heme oxygenase family apart from the canonical and IsdG/I families. Our studies provide insight into the enzymatic mechanisms and structure-function relationship of ChuZ.