Lactococcus lactis HemW (HemN) is a haem-binding protein with a putative role in haem trafficking
Lactococcus lactis HemW (HemN) is a haem-binding protein with a putative role in haem trafficking
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DOI：
10.1042/bj20111618
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发表时间：
2012-03-01
影响因子：
4.1
通讯作者：
Solioz, Marc
中科院分区：
文献类型：
--
作者：
Abicht, Helge K.;Martinez, Jacobo;Solioz, Marc
乳酸乳球菌不能合成血红素，但当供应血红素时，会表达一种细胞色素BD氧化酶。除了这种氧化酶的cydAB结构基因外，乳酸乳杆菌还具有另外两个基因hemH和hemW(Hemn)，推测它们在血红素代谢中具有功能。虽然似乎很清楚hemn编码一种铁络合酶，但hemW的功能尚不清楚。hemW样蛋白存在于细菌、植物和动物中，通常被注释为CPDHs(辅酶原III脱氢酶)。然而，这种功能从未被证明是针对一种类hemW蛋白的。我们在这里研究了乳酸乳杆菌的HEMW，结果表明它在体内和体外都没有CPDH活性。重组生产的纯化的HEMW含有铁-S(铁-硫)簇，是二聚体；失去铁后，蛋白质成为单体。这两种形式的蛋白质在体外都与血红素b共价结合，化学计量比为每个单体一个血红素，K-D为8MU M。在体内，血红蛋白以无血红素的胞浆形式和含有血红素的膜结合形式存在。将乳酸乳杆菌膜添加到含血红素的HEMW中，可在体外引发HEMW中的Hem释放。在这些发现的基础上，我们提出了HEMW在贩毒中的作用。类hemW蛋白形成了一个以前未被认识到的独特的系统发育分支。
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 hemN 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 K-D of 8 mu M. 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.