Structural basis of gating by the outer membrane transporter FecA

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Iron is essential for bacterial growth, and its acquisition often relies on high-affinity siderophore transporters.
• The FecA receptor in Escherichia coli is a key component of the ferric citrate uptake system, an important siderophore-mediated iron acquisition pathway.

Purpose of the Study:

• To elucidate the structural basis of ferric citrate binding and transport by the FecA outer membrane receptor.
• To understand the mechanism of ligand-induced conformational changes and signal propagation in siderophore receptors.

Main Methods:

• X-ray crystallography was used to determine the structure of FecA in complex with ferric citrate.
• High-resolution structural analysis was performed at 2.0 and 2.5 angstroms.

Main Results:

• The crystal structure revealed FecA comprises three domains: barrel, plug, and NH2-terminal extension.
• Ferric citrate binding induced a conformational change, closing the external pocket of FecA.
• The plug domain mediates signal propagation across the outer membrane, indicating receptor occupancy.

Conclusions:

• The study provides the structural foundation for understanding the gating mechanism in TonB-dependent outer membrane receptors.
• A mechanism for energy-dependent siderophore transport is proposed based on compiled data and structural insights.