FeoB contains a dual nucleotide-specific NTPase domain essential for ferrous iron uptake.

The Feo ferrous iron transporter is widely distributed among bacteria and archaea, but its mechanism of transport has not been fully elucidated. In , the transport system requires three proteins: the small cytosolic proteins FeoA and FeoC and a large cytoplasmic-membrane-associated protein FeoB, which has an N-terminal G-protein domain. We show that, in contrast to FeoB, which is solely a GTPase, the and FeoB proteins have both GTPase and ATPase activity. In , mutation of the G4 motif, responsible for hydrogen bonding with the guanine base, abolished the GTPase activity but not ATPase activity. The ATPase activity of the G4 motif mutants was sufficient for Feo function in the absence of GTPase. We show that the serine and asparagine residues in the G5 motif likely play a role in the ATPase activity, and substitution of these residues with those found in the corresponding positions in FeoB resulted in similar nucleotide hydrolysis activity in the protein. These results add significantly to our understanding of the NTPase domain of FeoB and its role in Feo function.