title: Lactococcus lactis HemW (HemN) is a haem-binding protein with a putative role in haem trafficking.
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.
authors.affiliation: Department Clinical Research, University of Bern, Murtenstrasse 35, Berne, Switzerland.
authors.forename: Helge K
authors.initials: HK
authors.lastname: Abicht
authors.forename: Jacobo
authors.initials: J
authors.lastname: Martinez
authors.forename: Gunhild
authors.initials: G
authors.lastname: Layer
authors.forename: Dieter
authors.initials: D
authors.lastname: Jahn
authors.forename: Marc
authors.initials: M
authors.lastname: Solioz
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003304:Coproporphyrinogen Oxidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D019281:Dimerization; D029968:Escherichia coli Proteins / Q000235:genetics; D005798:Genes, Bacterial; D006418:Heme / Q000378:metabolism*; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013294:Lactococcus lactis / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D003304:Coproporphyrinogen Oxidase; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D006418:Heme; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D011994:Recombinant Proteins; C109194:HemN protein, Bacteria