Department of Animal Biology, University of Hyderabad, Hyderabad, Telangana, India.
J Appl Microbiol. 2020 Dec;129(6):1733-1743. doi: 10.1111/jam.14728. Epub 2020 Jun 25.
To characterize the 21-kDa iron-regulated cell wall protein in Mycobacterium smegmatis co-expressed with the siderophores mycobactin, exochelin and carboxymycobactin upon iron limitation.
Mycobacterium smegmatis, grown in the presence of 0·02 μg Fe ml (low iron) produced high levels of all the three siderophores, which were repressed in bacteria supplemented with 8 μg Fe ml (high iron). Exochelin, the major extracellular siderophore was the first to rise and was expressed at high levels during log phase of growth. Carboxymycobactin, a minor component in log phase iron-starved M. smegmatis continued to rise when cultured for longer periods, reaching levels greater than exochelin. Iron-starved bacteria expressed a 21-kDa iron-regulated protein (IrpA) that was identified as Clp protease subunit (MSMEG_3671) and characterized as a receptor for ferri-exochelin.
Ferri-exochelin is the preferred siderophore in M. smegmatis and this ferri-exochelin: IrpA machinery is absent in Mycobacterium tuberculosis.
Exochelin machinery is functional in M. smegmatis and the carboxymycobactin-mycobactin machinery is the sole iron uptake system in M. tuberculosis. The absence of the ferri-exochelin: IrpA system in the pathogen signifies the importance of the carboxymycobactin-mycobactin system machinery in M. tuberculosis.
在缺铁条件下，与铁载体麦考酚酸、外铁载体和羧基麦考酚酸共表达时，对分枝杆菌中的 21kDa 铁调节细胞壁蛋白进行特征分析。
分枝杆菌在 0.02μg Fe/ml（低铁）存在下生长时产生高水平的所有三种铁载体，而在补充 8μg Fe/ml（高铁）的细菌中受到抑制。外铁载体是主要的细胞外铁载体，在对数生长期首次升高，并在生长对数期表达水平较高。分枝杆菌在缺铁的对数期，羧基麦考酚酸继续升高，当培养时间更长时，达到高于外铁载体的水平。缺铁细菌表达了一种 21kDa 的铁调节蛋白（IrpA），被鉴定为 Clp 蛋白酶亚基（MSMEG_3671），并被表征为铁外铁载体的受体。
铁外铁载体是分枝杆菌的首选铁载体，而这种铁外铁载体：IrpA 机制在结核分枝杆菌中不存在。
分枝杆菌中的外铁载体机制是功能性的，而分枝杆菌中的羧基麦考酚酸-麦考酚酸机制是唯一的铁摄取系统。病原体中缺乏铁外铁载体：IrpA 系统表明羧基麦考酚酸-麦考酚酸系统在结核分枝杆菌中的重要性。
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