1. Lactococcus lactis HemW (HemN) is a haem-binding protein with a putative role in haem trafficking.
- Author
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Abicht HK, Martinez J, Layer G, Jahn D, and Solioz M
- Subjects
- Amino Acid Sequence, Bacterial Proteins chemistry, Bacterial Proteins genetics, Base Sequence, Carrier Proteins chemistry, Carrier Proteins genetics, Coproporphyrinogen Oxidase chemistry, Coproporphyrinogen Oxidase genetics, DNA, Bacterial genetics, Dimerization, Escherichia coli Proteins genetics, Genes, Bacterial, Heme-Binding Proteins, Hemeproteins chemistry, Hemeproteins genetics, Lactococcus lactis genetics, Molecular Sequence Data, Phylogeny, Protein Structure, Quaternary, Recombinant Proteins chemistry, Recombinant Proteins genetics, Recombinant Proteins metabolism, Sequence Homology, Amino Acid, Bacterial Proteins metabolism, Carrier Proteins metabolism, Coproporphyrinogen Oxidase metabolism, Heme metabolism, Hemeproteins metabolism, Lactococcus lactis metabolism
- Abstract
Lactococcus lactis cannot synthesize haem, but when supplied with haem, expresses a cytochrome bd oxidase. Apart from the cydAB structural genes for this oxidase, L. lactis features two additional genes, hemH and hemW (hemN), with conjectured functions in haem metabolism. While it appears clear that hemH encodes a ferrochelatase, no function is known for hemW. HemW-like proteins occur in bacteria, plants and animals, and are usually annotated as CPDHs (coproporphyrinogen III dehydrogenases). However, such a function has never been demonstrated for a HemW-like protein. We here studied HemW of L. lactis and showed that it is devoid of CPDH activity in vivo and in vitro. Recombinantly produced, purified HemW contained an Fe-S (iron-sulfur) cluster and was dimeric; upon loss of the iron, the protein became monomeric. Both forms of the protein covalently bound haem b in vitro, with a stoichiometry of one haem per monomer and a KD of 8 μM. In vivo, HemW occurred as a haem-free cytosolic form, as well as a haem-containing membrane-associated form. Addition of L. lactis membranes to haem-containing HemW triggered the release of haem from HemW in vitro. On the basis of these findings, we propose a role of HemW in haem trafficking. HemW-like proteins form a distinct phylogenetic clade that has not previously been recognized.
- Published
- 2012
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