2.A.100.2.1
Ferroportin of 440 aas and 12 TMSs. Transports Fe²⁺, Co²⁺, Mn²⁺ and Ni²⁺. The 3-d structures in both the inward and outward facing orientations have been determined, showing similarities to those of MFS permeases (Taniguchi et al. 2015). The Fpn family is a member of the MFS. Fpn-mediated iron efflux is stimulated by extracellular Ca²⁺ in the physiological range, even though  Ca²⁺ is not transported. Deshpande et al. 2018 determined the crystal structure of Ca²⁺-bound BbFpn (TC# 2.A.100.2.1), and found that Ca²⁺ is a cofactor that facilitates a conformational change critical to the transport cycle. They also identified a substrate pocket accommodating a divalent transition metal complexed with a chelator. These findings support a model of iron export by Fpn and suggest a link between plasma calcium and iron homeostasis (Deshpande et al. 2018).