The Nickel/cobalt Transporter (NicO) Family
Homologues of the NicO family have differing predicted topologies: 6, 7 and 8 TMSs. One such homologue, RcnA (YohM) of E. coli (274 aas) has 6 putative TMSs in a 3+3 arrangement with a large hydrophilic loop between putative TMSs 3 and 4. This protein is believed to catalyze Co2+ and Ni2+ efflux (Rodrique et al., 2005). Several homologues of RcnA (e.g., from Ralstonia solanacearum; CAD17703) have 7 putative TMSs (4+3). 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 . This family within the LysE superfamily may have a common orign with the TOG superfamily, having lost TMSs 1 and 4 in the 8 TMS TOG superfamily topology.
The overall reaction catalyzed by proteins of the NicO family is probably:
[Ni2+ or Co2+] (in) [Ni2+ or Co2+] (out).