This family contains phosphate regulatory proteins including PhoU. PhoU proteins are known to play a role in the regulation of phosphate uptake. The PhoU domain is composed of a three helix bundle [1]. The PhoU protein contains two copies of this domain. The domain binds to an iron cluster via its conserved E/DXXXD motif.

1: Crystal structure of a PhoU protein homologue: a new class of metalloprotein containing multinuclear iron clusters. Liu J, Lou Y, Yokota H, Adams PD, Kim R, Kim SH; J Biol Chem. 2005;280:15960-15966. PMID:15716271