Lactococcus lactis HemW (HemN) is a haem-binding protein with a putative role in haem trafficking

Abicht, Helge K; Martinez, Jacobo; Layer, Gunhild; Jahn, Dieter; Solioz, Marc (2012). Lactococcus lactis HemW (HemN) is a haem-binding protein with a putative role in haem trafficking. Biochemical journal, 442(2), pp. 335-43. London: Portland Press 10.1042/BJ20111618

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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.

Item Type:

Journal Article (Original Article)


04 Faculty of Medicine > Department of Gastro-intestinal, Liver and Lung Disorders (DMLL) > Clinic of Visceral Surgery and Medicine > Hepatology

UniBE Contributor:

Solioz, Marc




Portland Press




Factscience Import

Date Deposited:

04 Oct 2013 14:38

Last Modified:

05 Dec 2022 14:11

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URI: (FactScience: 222516)

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