1po3
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Crystal structure of ferric citrate transporter FecA in complex with ferric citrate
OverviewOverview
Escherichia coli possesses a TonB-dependent transport system, which, exploits the iron-binding capacity of citrate and its natural abundance., Here, we describe three structures of the outer membrane ferric citrate, transporter FecA: unliganded and complexed with iron-free or diferric, dicitrate. We show the structural mechanism for discrimination between the, iron-free and ferric siderophore: the binding of diferric dicitrate, but, not iron-free dicitrate alone, causes major conformational rearrangements, in the transporter. The structure of FecA bound with iron-free dicitrate, represents the first structure of a TonB-dependent transporter bound with, an iron-free siderophore. Binding of diferric dicitrate to FecA results in, changes in the orientation of the two citrate ions relative to each other, and in their interactions with FecA, compared to the binding of iron-free, dicitrate. The changes in ligand binding are accompanied by conformational, changes in three areas of FecA: two extracellular loops, one plug domain, loop and the periplasmic TonB-box motif. The positional and conformational, changes in the siderophore and transporter initiate two independent, events: ferric citrate transport into the periplasm and transcription, induction of the fecABCDE transport genes. From these data, we propose a, two-step ligand recognition event: FecA binds iron-free dicitrate in the, non-productive state or first step, followed by siderophore displacement, to form the transport-competent, diferric dicitrate-bound state in the, second step.
About this StructureAbout this Structure
1PO3 is a Single protein structure of sequence from Escherichia coli with FLC and FE as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Structural evidence for iron-free citrate and ferric citrate binding to the TonB-dependent outer membrane transporter FecA., Yue WW, Grizot S, Buchanan SK, J Mol Biol. 2003 Sep 12;332(2):353-68. PMID:12948487
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