PDBsum entry 1po3

Membrane protein

PDB id: 1po3

Contents

Protein chains

647 a.a. *

Ligands

FLC ×4

Metals

_FE ×4

* Residue conservation analysis

PDB id:

1po3

Name:

Membrane protein

Title:

Crystal structure of ferric citrate transporter feca in complex with ferric citrate

Structure:

Iron(iii) dicitrate transport protein feca precursor. Chain: a, b. Fragment: feca residues 95-741. Engineered: yes

Source:

Escherichia coli. Organism_taxid: 562. Gene: feca or b4291. Expressed in: escherichia coli bl21. Expression_system_taxid: 511693.

Resolution:

3.40Å R-factor: 0.239 R-free: 0.314

Authors:

W.W.Yue,S.Grizot,S.K.Buchanan

Key ref:

W.W.Yue et al. (2003). Structural evidence for iron-free citrate and ferric citrate binding to the TonB-dependent outer membrane transporter FecA. J Mol Biol, 332, 353-368. PubMed id: 12948487 DOI: 10.1016/S0022-2836(03)00855-6

Date:

13-Jun-03 Release date: 18-Nov-03

Protein chains

P13036  (FECA_ECOLI) -  Fe(3+) dicitrate transport protein FecA from Escherichia coli (strain K12)

Seq: 774 a.a.

Struc: 647 a.a.

DOI no: 10.1016/S0022-2836(03)00855-6

J Mol Biol 332:353-368 (2003)

PubMed id: 12948487

Structural evidence for iron-free citrate and ferric citrate binding to the TonB-dependent outer membrane transporter FecA.

W.W.Yue, S.Grizot, S.K.Buchanan.

ABSTRACT

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.

Selected figure(s)

Figure 2.
Figure 2. Crystal structures of FecA unliganded (a, FecA[apo]), bound with iron-free dicitrate (b, FecA[Cit]) and with diferric dicitrate (c, FecA[FeCit]), viewed perpendicular to the barrel axis. In all three structures, the overall fold consists of a 22-stranded b-barrel (yellow) preceded by a plug domain (magenta) that fits into the barrel lumen. Iron-free dicitrate and diferric dicitrate (green) are depicted in space-filling representation (with iron atoms in red). The two extracellular loops L7 and L8, which are involved in conformational changes upon binding of diferric dicitrate, are colored blue. The TonB box motifs in FecA[apo] and FecA[Cit] are circled. Part of the barrel has been rendered transparent to reveal the plug domain located in the barrel lumen.

Figure 6.
Figure 6. C^a superposition of the plug domains in FecA, FepA and FhuA. The structures of FecA[apo] (gold), FepA (magenta) and unliganded FhuA (light blue) were used for the superposition. The TonB box motifs of FecA[apo] and FepA are circled.

The above figures are reprinted by permission from Elsevier: J Mol Biol (2003, 332, 353-368) copyright 2003.

Figures were selected by the author.