The coproporphyrin ferrochelatase of Staphylococcus aureus: mechanistic insights into a regulatory iron-binding site.
The coproporphyrin ferrochelatase of Staphylococcus aureus: mechanistic insights into a regulatory iron-binding site.
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DOI：
10.1042/bcj20170362
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发表时间：
2017-10-10
期刊：
影响因子：
--
通讯作者：
Shepherd M
中科院分区：
文献类型：
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作者：
Hobbs C;Reid JD;Shepherd M
大多数特有的铁络合酶催化经典的血红素合成的最后一步，将亚铁插入原卟啉IX。然而，对于最近发现的依赖于复合卟啉的途径，铁络合酶催化倒数第二个反应，其中亚铁被插入到复合卟啉III中。细菌门的铁络合酶和放线杆菌的铁络合酶以前已经被证明将铁插入到复合卟啉中，而来自枯草杆菌和金黄色葡萄球菌的铁络合酶被已知的高铁浓度所抑制。本文报道了金黄色葡萄球菌铁络合酶的Km(共卟啉III)为1.5 µM，结果表明，提高铁浓度会增加共卟啉III的Km，为观察到的铁介导的底物抑制提供了一个潜在的解释。结构建模、定点突变和动力学分析共同证实了残基Glu271是铁与金黄色葡萄球菌铁络合酶抑制调控位点结合所必需的，为观察到的底物抑制模式提供了分子解释。因此，这项工作对金黄色葡萄球菌中血红素的生物合成如何受铁的供应进行调节具有重要意义。
The majority of characterised ferrochelatase enzymes catalyse the final step of classical haem synthesis, inserting ferrous iron into protoporphyrin IX. However, for the recently discovered coproporphyrin-dependent pathway, ferrochelatase catalyses the penultimate reaction where ferrous iron is inserted into coproporphyrin III. Ferrochelatase enzymes from the bacterial phyla Firmicutes and Actinobacteria have previously been shown to insert iron into coproporphyrin, and those from Bacillus subtilis and Staphylococcus aureus are known to be inhibited by elevated iron concentrations. The work herein reports a Km (coproporphyrin III) for S. aureus ferrochelatase of 1.5 µM and it is shown that elevating the iron concentration increases the Km for coproporphyrin III, providing a potential explanation for the observed iron-mediated substrate inhibition. Together, structural modelling, site-directed mutagenesis, and kinetic analyses confirm residue Glu271 as being essential for the binding of iron to the inhibitory regulatory site on S. aureus ferrochelatase, providing a molecular explanation for the observed substrate inhibition patterns. This work therefore has implications for how haem biosynthesis in S. aureus is regulated by iron availability.