FeoB is a transmembrane protein involved in ferrous iron uptake in prokaryotic organisms. FeoB comprises a cytoplasmic soluble domain termed NFeoB and a C-terminal polytopic transmembrane domain. Recent structures of NFeoB have revealed two structural subdomains: a canonical GTPase domain and a five-helix helical domain. The GTPase domain hydrolyses GTP to GDP through a well characterized mechanism, a process which is required for Fe2+transport. In contrast, the precise role of the helical domain has not yet been fully determined. Here, the structure of the cytoplasmic domain of FeoB from
Gallionella capsiferriformansis reported. Unlike recent structures of NFeoB, the G. capsiferriformansNFeoB structure is highly unusual in that it does not contain a helical domain. The crystal structures of both apo and GDP-bound protein forms a domain-swapped dimer.