Discovery of a siderophore export system essential for virulence of Mycobacterium tuberculosis
| Autor: | Kathryn S. Doornbos, Zhaoyong Xi, Peibei Sun, Michael Niederweis, Ryan M. Wells, Alexander Speer, Olga Danilchanka, Changlin Tian, Christopher M. Jones, Fangming Wu |
|---|---|
| Rok vydání: | 2012 |
| Předmět: |
Siderophore
Mutant Siderophores Biochemistry Mice Microbial Physiology Biology (General) Lung Oxazoles Sequence Deletion 0303 health sciences Mice Inbred BALB C Virulence Lipids 3. Good health Transport protein Bacterial Pathogens Survival Rate Host-Pathogen Interaction Host-Pathogen Interactions Female Bacterial Outer Membrane Proteins Research Article Protein Structure QH301-705.5 Iron Immunology Mycobactin Receptors Cell Surface Biology Microbiology 03 medical and health sciences Bacterial Proteins Virology Genetics Animals Tuberculosis Secretion Molecular Biology 030304 developmental biology 030306 microbiology Proteins Periplasmic space Mycobacterium tuberculosis RC581-607 Protein Structure Tertiary Membrane protein Parasitology Chromatography Thin Layer Immunologic diseases. Allergy Carrier Proteins Spleen |
| Zdroj: | PLoS Pathogens PLoS Pathogens, Vol 9, Iss 1, p e1003120 (2013) |
| ISSN: | 1553-7374 |
| Popis: | Iron is an essential nutrient for most bacterial pathogens, but is restricted by the host immune system. Mycobacterium tuberculosis (Mtb) utilizes two classes of small molecules, mycobactins and carboxymycobactins, to capture iron from the human host. Here, we show that an Mtb mutant lacking the mmpS4 and mmpS5 genes did not grow under low iron conditions. A cytoplasmic iron reporter indicated that the double mutant experienced iron starvation even under high-iron conditions. Loss of mmpS4 and mmpS5 did not change uptake of carboxymycobactin by Mtb. Thin layer chromatography showed that the ΔmmpS4/S5 mutant was strongly impaired in biosynthesis and secretion of siderophores. Pull-down experiments with purified proteins demonstrated that MmpS4 binds to a periplasmic loop of the associated transporter protein MmpL4. This interaction was corroborated by genetic experiments. While MmpS5 interacted only with MmpL5, MmpS4 interacted with both MmpL4 and MmpL5. These results identified MmpS4/MmpL4 and MmpS5/MmpL5 as siderophore export systems in Mtb and revealed that the MmpL proteins transport small molecules other than lipids. MmpS4 and MmpS5 resemble periplasmic adapter proteins of tripartite efflux pumps of Gram-negative bacteria, however, they are not only required for export but also for efficient siderophore synthesis. Membrane association of MbtG suggests a link between siderophore synthesis and transport. The structure of the soluble domain of MmpS4 (residues 52–140) was solved by NMR and indicates that mycobacterial MmpS proteins constitute a novel class of transport accessory proteins. The bacterial burden of the mmpS4/S5 deletion mutant in mouse lungs was lower by 10,000-fold and none of the infected mice died within 180 days compared to wild-type Mtb. This is the strongest attenuation observed so far for Mtb mutants lacking genes involved in iron utilization. In conclusion, this study identified the first components of novel siderophore export systems which are essential for virulence of Mtb. Author Summary In the late 19th century the French physician Armand Trousseau recognized that treating anemic tuberculosis patients with iron salts exacerbated the disease. In 1911 Twort postulated that mycobacteria produce an essential growth factor which was identified in 1953 as mycobactin. The hydrophobic mycobactin and its more water-soluble cousin carboxymycobactin are small molecules made by Mycobacterium tuberculosis to scavenge iron from its human host. While the biosynthesis of these siderophores has been decoded, it was unknown how M. tuberculosis secretes these molecules. In this study, we identified two similar transport systems, MmpS4/MmpL4 and MmpS5/MmpL5, which are required for biosynthesis and export of siderophores by M. tuberculosis. The lack of these transport systems drastically decreased the number of M. tuberculosis cells in the lungs and spleens of infected mice. Lung examination and histological assessment in mice infected with the mmpS4/S5 deletion strain showed almost no signs of infection. Further, none of the mice infected with this strain died within 180 days in contrast to wild-type M. tuberculosis. In this study, we identified the first components of a novel siderophore export system in M. tuberculosis and showed the importance of siderophore export for virulence of M. tuberculosis. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|