Biochemical and Proteomic Analyses of Mycobacterial Heme Uptake

描述（由申请人提供）：结核分枝杆菌（Mycobacterium tuberculosis，Mtb）是结核病（TB）的病原体，仍然是困扰世界人口的最致命的疾病之一，因此迫切需要新的抗TB治疗剂。铁是结核杆菌生存的必需品，它必须从宿主中分离出来。这些拟议的研究围绕着新发现的新的分枝杆菌血红素铁获取途径。最近，Mtb细胞溶质血红素降解蛋白，MhuD，已被表征，其中MhuD通过血红素四吡咯环的裂解催化铁从血红素的释放。然而，Mtb mhuD缺失突变体并没有完全消除血红素存在下的生长，这表明另一种未发现的蛋白质也具有从血红素释放铁的功能。我们认为，Mtb染料脱色过氧化物酶（Mtb Dyp）可以从血红素中提取铁，而不需要四吡咯环的断裂，因为Mtb Dyp与E.以这种方式发挥作用的大肠杆菌蛋白质。此外，Mtb还具有分泌的EkB蛋白同源物（Enc），与Mtb Dyp形成双基因操纵子。提出这些蛋白质经由Mtb Dyp中的延伸C-末端延伸相互作用，由此Mtb Dyp被Mtb Enc纳米笼包封。有趣的是，我们还观察到Mtb铁结合铁蛋白Mtb BfrB也含有延伸的C末端尾，并且可能表明Mtb BfrB也被Mtb Enc区室化。该提案概述了一个务实的结构，生化和遗传的方法来表征血红素降解功能的Mtb Dyp，沿着与Mtb Enc的相互作用。因此，本研究的结果不仅将进一步加深我们对Mtb血红素铁摄取和利用的理解，而且还将为开发创新的抗TB疗法提供新的候选物，Mtb Dyp和Mtb Enc，它们没有真核同源物。

DESCRIPTION (provided by applicant): Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is still one of the most deadly diseases afflicting the world's population, therefore novel anti-TB therapeutics are urgently needed. Iron is an essential for Mtb survival, which it must sequester from its host. These proposed studies center around the newly discovered, novel mycobacterial heme-iron acquisition pathway. Recently, an Mtb cytosolic heme-degrading protein, MhuD, has been characterized, whereby MhuD catalyzes the release of iron from heme by cleavage of the heme tetrapyrrole ring. However, an Mtb mhuD deletion mutant did not completely abolish growth in the presence of heme, suggesting that another undiscovered protein is also functioning to release iron from heme. We propose that Mtb dye-decolorizing peroxidase, Mtb Dyp, may abstract iron from heme without the cleavage of the tetrapyrrole ring, as Mtb Dyp is a close homolog to E. coli proteins which function in this manner. Furthermore, Mtb also harbors a secreted encapsulin homolog (Enc), forming a two-gene operon with Mtb Dyp. These proteins are proposed to interact via an extended C-terminal extension in Mtb Dyp, whereby Mtb Dyp is encapsulated by Mtb Enc nano-cage. Interestingly, we have also observed that an Mtb iron-binding ferritin protein, Mtb BfrB, also contains an extended C-terminal tail, and may indicate that Mtb BfrB is also be compartmentalized by Mtb Enc. This proposal outlines a pragmatic structural, biochemical and genetic approach to characterize the heme-degrading function of Mtb Dyp, along with its interaction with Mtb Enc. Thus results from this study will not only further our understanding of Mtb heme-iron uptake and utilization but will also provide new candidates, Mtb Dyp and Mtb Enc, which have no eukaryotic homologues, for the development of innovative anti-TB therapeutics.