FecA transmembrane channel. Molecular model of the FecA membrane transporter protein in its beta-barrel configuration. This protein aids the transport of siderophores (iron-carrying compounds) across cell membranes, in this case it facilitates uptake of iron by the Escherichia coli bacterium. Transporter FecA is an example of a ligand-gated outer membrane channel. This outer membrane protein is also part of the family of TonB-dependent receptors. The barrel shape is known as the plug domain.