The events of signal transduction in ligand-gated channel proteins at an atomic level are of great interest for the understanding of the mechanism of signaling, both in terms of transmission and coordination. Although quite different in many respects, the FhuA protein appears as an excellent conceptual model for receptor proteins also in eukaryotic systems. The architecture of the FhuA protein has been predicted to be that of a β-barrel, analogous to the porins. The structure of the ligand-gated FhuA protein may have heuristic value for the concepts of structure and mechanistic properties of eukaryotic membrane receptors with similar functions. The first step of iron import into Gram-negative organisms is the transport of ferric ions, in complex with siderophores, across the bacterial outer membrane. The presence of two types of secondary structures within membrane boundaries may not be restricted to this protein, rendering not only predictions, but also the interpretation of spectroscopic results of membrane proteins even more difficult.