A genetic locus required for iron acquisition in Mycobacterium tuberculosis

Abstract

Mycobactins are a family of membrane-associated siderophores required for Mycobacterium tuberculosis to adapt to its intracellular habitat. These lipophilic siderophores have been recently shown to directly acquire intracellular iron through lipid trafficking. Despite tremendous progress in understanding the assemblyline enzymology of the siderophore biosynthesis, the genes as well as the mechanistic and biochemical principles involved in producing membrane-associated siderophores have not been investigated. Here, we report a biosynthetic locus that incorporates variety of aliphatic chains on the mycobactin skeleton. Cell-free reconstitution studies demonstrate that these acyl chains are directly transferred from a carrier protein on to the -amino group of lysine residue by an unidentified Rv1347c gene product. The unsaturation in the lipidic chain is produced by a novel acyl-acyl carrier protein dehydrogenase, which, in contrast to the conventional acyl-CoA dehydrogenases, is involved in the biosynthetic pathway. MbtG protein then performs the final N6-hydroxylation step. Genome-wide analysis revealed homologues of N-acyl transferase and MbtG in other pathogenic bacteria. Because iron plays a key role in the development of infectious diseases, the biosynthetic pathway described here represents an attractive target for developing new antibacterial agents.biosynthesis ͉ mycobactin ͉ siderophore ͉ acyl-transferase ͉ dehydrogenase

Lipidomic discovery of deoxysiderophores reveals a revised mycobactin biosynthesis pathway in Mycobacterium tuberculosis

“…Seminal work showed that mycobactin synthases, named MbtA-N, are encoded at two loci (6,9,10). IdeR controls siderophore biosynthesis by repressing transcription of mbtA-N in iron-replete conditions (9)(10)(11). The predicted functions of MbtA-N fit well into widely accepted theoretical models for the production of mycobactin, but the functions of most genes and intermediates in mycobactin biosynthesis have not been directly established (5,6,9,10).…”

“…First, they are high-affinity, hexadentate iron ligands. Second, they neutralize the Fe 3+ cation and tether it to a lipid tail, promoting iron transport across the hydrophobic membranes (8)(9)(10). Both lipids contain the same peptide.…”

“…Whereas mycobactin biosynthesis is a known virulence-conferring pathway, the precise mechanisms by which mycobactins are produced and cycled through the cell wall are incompletely understood. Seminal work showed that mycobactin synthases, named MbtA-N, are encoded at two loci (6,9,10). IdeR controls siderophore biosynthesis by repressing transcription of mbtA-N in iron-replete conditions (9)(10)(11).…”

“…IdeR controls siderophore biosynthesis by repressing transcription of mbtA-N in iron-replete conditions (9)(10)(11). The predicted functions of MbtA-N fit well into widely accepted theoretical models for the production of mycobactin, but the functions of most genes and intermediates in mycobactin biosynthesis have not been directly established (5,6,9,10). Here we describe the development and application of mycobacterial lipidomics to identify deoxysiderophore intermediates that are inconsistent with the current model of mycobactin biosynthesis and lead to a new general mechanism of biosynthesis.…”

Increased expression of host iron-binding proteins precedes iron accumulation and calcification of primary lung lesions in experimental tuberculosis in the guinea pig

“…Iron is a cofactor for numerous heme and non-heme proteins that are involved in critical metabolic functions that are common to all living organisms (21,22). M. tuberculosis like other pathogenic bacteria has evolved complex mechanisms to acquire host iron which is limited in vivo even under normal physiologic conditions (30,31,45,46). It was the observations from in vitro studies, that M. tuberculosis can scavenge host iron that led us to hypothesize that iron accumulated in the primary lung lesions in the guinea pig model of tuberculosis.…”