Iron-starved Mycobacterium tuberculosis utilises the carboxymycobactin-mycobactin siderophore machinery to acquire iron. These two siderophores have high affinity for ferric iron and can withdraw the metal ion from insoluble iron hydroxides and iron-binding proteins. We first reported HupB, a multi-functional mycobacterial protein to be associated with iron acquisition in M. tuberculosis. This 28 kDa cell wall protein, up regulated upon iron limitation functions as a transcriptional activator of mycobactin biosynthesis and is essential for the pathogen to survive inside macrophages. The focus of this study is to understand the role of HupB in iron uptake and transport by the carboxmycobactin-mycobactin siderophore machinery in M. tuberculosis. Experimental approaches included radiolabelled iron uptake studies by viable organisms and protein–ligand binding studies using the purified HupB and the two siderophores. Uptake of ⁵⁵Fe-carboxymycobactin by wild type M. tuberculosis (WT M.tb.H37Rv) and not by the hupB KO mutant (M.tb.ΔhupB) showed that HupB is necessary for the uptake of ferri-carboxymycobactin. Additionally, the radiolabel recovery was high in HupB-incorporated liposomes upon addition of the labelled siderophore. Bioinformatic and experimental studies using spectrofluorimetry, CD analysis and surface plasmon resonance not only confirmed the binding of HupB with ferri-carboxymycobactin and ferri-mycobactin but also with free iron. In conclusion, HupB is established as a ferri- carboxymycobactin receptor and by virtue of its property to bind ferric iron, functions as a transporter of the ferric iron from the extracellular siderophore to mycobactin within the cell envelope.

缺铁的结核分枝杆菌利用羧基分枝杆菌素-分枝杆菌素铁载体机制来获取铁。这两种铁载体对三价铁具有高亲和力，可以从不溶性铁氢氧化物和铁结合蛋白中提取金属离​​子。我们首先报道了 HupB，一种与结核分枝杆菌铁获取相关的多功能分枝杆菌蛋白。这种 28 kDa 的细胞壁蛋白，在铁限制后上调，作为分枝杆菌素生物合成的转录激活剂，对病原体在巨噬细胞内生存至关重要。本研究的重点是了解 HupB 在结核分枝杆菌中羧霉菌素-霉菌素铁载体机制对铁的吸收和转运中的作用. 实验方法包括活生物体的放射性标记铁摄取研究和使用纯化的 HupB 和两种铁载体的蛋白质-配体结合研究。野生型结核分枝杆菌(WT M.tb. H37Rv) 而非hupB KO 突变体 ( M.tb.ΔhupB )摄取⁵⁵ Fe-羧基霉菌素) 表明 HupB 是吸收铁羧基霉菌素所必需的。此外，添加标记的铁载体后，结合 HupB 的脂质体的放射性标记回收率很高。使用荧光分光光度法、CD 分析和表面等离子共振的生物信息学和实验研究不仅证实了 HupB 与铁-羧基霉菌素和铁-霉菌素的结合，而且还证实了与游离铁的结合。总之，HupB 被确定为铁-羧基霉菌素受体，并且由于其结合三价铁的特性，作为三价铁从细胞外铁载体到细胞包膜内的分枝杆菌素的转运蛋白。