A Single Mutation in the Mycobacterium tuberculosis Heme-Degrading Protein, MhuD, Results in Different Products
A Single Mutation in the Mycobacterium tuberculosis Heme-Degrading Protein, MhuD, Results in Different Products
复制标题
DOI：
10.1021/acs.biochem.8b01198
复制
发表时间：
2019-02-12
期刊：
影响因子：
2.9
通讯作者：
Goulding, Celia W.
中科院分区：
文献类型：
--
作者：
Chao, Alex;Goulding, Celia W.
结核分枝杆菌血红素降解蛋白MhuD将血红素降解为胆绿素异构体和铁，而来自金黄色葡萄球菌的与其最相近的同系物IsdG和IsdI则将血红素降解为葡萄球菌胆绿素异构体、甲醛和铁。血红素结合复合物的结构叠加显示，MhuD活性位点中的血红素分子相对于IsdG和IsdI活性位点的血红素分子围绕四吡咯平面旋转了约90度。因此，IsdG/IsdI和MhuD生色团产物的差异可能归因于不同的血红素取向。在MhuD中，两个精氨酸Arg22和Arg26稳定血红素的丙酸酯，并可能是血红素取向的原因。在此，我们证明MhuD - R26S变体将产生的生色团产物从胆绿素改变为胆绿素IXα（α - BV），而R22S变体则不会。令人惊讶的是，与也将血红素降解为α - BV的经典血红素加氧酶（HO）不同，MhuD - R26S变体产生C1产物甲醛，而非如HO所观察到的一氧化碳。MhuD - R26S变体是进一步探究MhuD作用机制以及研究结核分枝杆菌中MhuD产物去向的重要工具。
Mycobacterium tuberculosis heme-degrading protein MhuD degrades heme to mycobilin isomers and iron, while its closest homologues from Staphylococcus aureus, IsdG and IsdI, degrade heme to staphylobilin isomers, formaldehyde, and iron. Superposition of the structures of the heme-bound complexes reveals that the heme molecule in the MhuD active site is rotated similar to 90 degrees about the tetrapyrrole plane with respect to IsdG and IsdI active site heme molecules. Therefore, the variation in IsdG/IsdI and MhuD chromophore products may be attributed to the different heme orientations. In MhuD, two arginines, Arg22 and Arg26, stabilize the heme propionates and may account for the heme orientation. Herein, we demonstrate that the MhuD-R26S variant alters the resulting chromophore product from mycobilin to biliverdin IX alpha (alpha-BV), whereas the R22S variant does not. Surprisingly, unlike canonical heme oxygenase (HO) that also degrades heme to alpha-BV, the MhuD-R26S variant produces the C1 product formaldehyde rather than carbon monoxide as observed for HO. The MhuD-R26S variant is an important tool for further probing the mechanism of action of MhuD and for studying the fate of the MhuD product in mycobacterium.