A new class of [2Fe-2S]-cluster-containing protoporphyrin (IX) ferrochelatases.
Protoporphyrin (IX) ferrochelatase catalyses the insertion of ferrous iron into protoporphyrin IX to form haem. These ferrochelatases exist as monomers and dimers, both with and without [2Fe-2S] clusters. The motifs for [2Fe-2S] cluster co-ordination are varied, but in all cases previously reported, three of the four cysteine ligands are present in the 30 C-terminal residues and the fourth ligand is internal. In the present study, we demonstrate that a group of micro-organisms exist which possess protoporphyrin (IX) ferrochelatases containing [2Fe-2S] clusters that are co-ordinated by a group of four cysteine residues contained in an internal amino acid segment of approx. 20 residues in length. This suggests that these ferrochelatases have evolved along a different lineage than other bacterial protoporphyrin (IX) ferrochelatases. For example, Myxococcus xanthus protoporphyrin (IX) ferrochelatase ligates a [2Fe-2S] cluster via cysteine residues present in an internal segment. Site-directed mutagenesis of this ferrochelatase demonstrates that changing one cysteine ligand into serine results in loss of the cluster, but unlike eukaryotic protoporphyrin (IX) ferrochelatases, this enzyme retains its activity. These data support a role for the [2Fe-2S] cluster in iron affinity, and strongly suggest convergent evolution of this feature in prokaryotes.
Shepherd
Mark
M
Biomedical and Health Sciences Institute, Paul D. Coverdell Center, University of Georgia, Athens, GA 30602, USA.
Dailey
Tamara A
TA
Dailey
Harry A
HA
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016935:Caulobacter crescentus / Q000201:enzymology; D003001:Cloning, Molecular; D003553:Cystine; D019143:Evolution, Molecular; D005294:Ferrochelatase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007501:Iron / Q000032:analysis*; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009169:Mycobacterium tuberculosis / Q000201:enzymology; D011524:Protoporphyrins / Q000378:metabolism*; D013455:Sulfur / Q000032:analysis*
D001426:Bacterial Proteins; D008565:Membrane Proteins; D011524:Protoporphyrins; D003553:Cystine; D013455:Sulfur; C028025:protoporphyrin IX; D007501:Iron; D005294:Ferrochelatase