PT  - JOURNAL ARTICLE
AU  - Inokentijs Josts
AU  - Katharina Veith
AU  - Henning Tidow
TI  - Crystal structures of the outer membrane transporter FoxA provide novel insights into TonB-mediated siderophore uptake and signalling
AID  - 10.1101/621219
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 621219
4099  - http://biorxiv.org/content/early/2019/04/28/621219.short
4100  - http://biorxiv.org/content/early/2019/04/28/621219.full
AB  - Many microbes and fungi acquire the essential ion Fe3+ through the synthesis and secretion of high-affinity chelators termed siderophores. In Gram-negative bacteria, these ferric-siderophore complexes are actively taken up using highly specific TonB-dependent transporters (TBDTs) located in the outer bacterial membrane (OM). However, the detailed mechanism of how the inner-membrane protein TonB connects to the transporters in the OM as well as the interplay between siderophore- and TonB-binding to the transporter is still poorly understood. Here, we present three crystal structures of the TBDT FoxA from Pseudomonas aeruginosa (containing a signalling domain) in complex with the siderophore ferrioxamine B and TonB and combine them with a detailed analysis of binding constants. The structures show that both siderophore and TonB-binding is required to form a translocation-competent state of the FoxA transporter in a two-step TonB-binding mechanism. The complex structure also indicates how TonB-binding influences the orientation of the signalling domain.ASUasymmetric unitEPRelectron paramagnetic resonanceFoaBferrioxamine BMSP1D1membrane scaffold protein variant D1IMinner membraneIPTGisopropyl β-D-1-thiogalactopyranosideITCisothermal titration calorimetryNDnanodiscNGnonyl glucopyranosideNi-NTANi-nitrilotriacetic acidOMouter membraneOGoctyl glucopyranosidePOPC1-palmitoyl-2-oleoyl-glycero-3-phosphocholineTBDTTonB-dependent transporterTEVtobacco etch virus.