Import into Mycobacterium tuberculosis with exporters

The pathogen Mycobacterium tuberculosis still kills over a million people per year. The survival of M. tuberculosis relies on importing necessary nutrients from the host, including iron and vitamin B₁₂. In two papers in Nature, the structure and mechanism of the proteins responsible for this import are revealed. Dirk Slotboom and colleagues report the structure of Rv1819c, an ABC transporter that imports hydrophilic compounds such as vitamin B₁₂, despite having an exporter fold. Markus Seeger and colleagues then report the structure of IrtAB4, which imports siderophores (iron-chelating compounds produced by the bacterium), also with an exporter fold. IrtAB4 has a siderophore interaction domain that sits near the membrane inner leaflet, allowing the reduction of the siderophore and uptake of iron by M. tuberculosis.