The Nickel/Cobalt Transporter (NicO) Family is a member of the Lysine Exporter (LysE) Superfamily.
[1] Homologues of the NicO family have differing predicted topologies: 6, 7 and 8 TMSs.
One such homologue, RcnA (YohM; TC# 2.A.113.1.1) of E. coli (274 aas) has 6 putative transmembrane segments (TMSs) in a 3 + 3 arrangement with a large hydrophilic loop between putativeTMSs 3 and 4.
Still another homologue, UreH of Methanocaldococcus janaschii (TC# 2.A.113.1.4) has 6 putative TMSs in a more characteristic 3 + 3 TMS arrangement.
[2] The overall reaction catalyzed by proteins of the NicO family is probably: [Ni2+ or Co2+] (in) → [Ni2+ or Co2+] (out).