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.
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Research Article|
February 13 2012
Lactococcus lactis HemW (HemN) is a haem-binding protein with a putative role in haem trafficking
Helge K. Abicht;
Helge K. Abicht
*Department Clinical Research, University of Bern, Murtenstrasse 35, 3010 Berne, Switzerland
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Jacobo Martinez;
Jacobo Martinez
†Department of Biology, Chemistry and Pharmacy, Free University of Berlin, Takustrasse 6, 14195 Berlin, Germany
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Gunhild Layer;
Gunhild Layer
‡Institute of Microbiology, Technical University Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany
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Dieter Jahn;
Dieter Jahn
‡Institute of Microbiology, Technical University Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany
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Marc Solioz
Marc Solioz
1
*Department Clinical Research, University of Bern, Murtenstrasse 35, 3010 Berne, Switzerland
1To whom correspondence should be addressed (email marc@solioz-scientific.ch).
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Publisher: Portland Press Ltd
Received:
September 07 2011
Revision Received:
November 14 2011
Accepted:
December 05 2011
Accepted Manuscript online:
December 05 2011
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2012 Biochemical Society
2012
Biochem J (2012) 442 (2): 335–343.
Article history
Received:
September 07 2011
Revision Received:
November 14 2011
Accepted:
December 05 2011
Accepted Manuscript online:
December 05 2011
Citation
Helge K. Abicht, Jacobo Martinez, Gunhild Layer, Dieter Jahn, Marc Solioz; Lactococcus lactis HemW (HemN) is a haem-binding protein with a putative role in haem trafficking. Biochem J 1 March 2012; 442 (2): 335–343. doi: https://doi.org/10.1042/BJ20111618
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