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 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).

This family belongs to the: LysE Superfamily.

References associated with 2.A.113 family:

Marrero, J., G. Auling, O. Coto, and D.H. Nies. (2007). High-level resistance to cobalt and nickel but probably no transenvelope efflux: Metal resistance in the Cuban Serratia marcescens strain C-1. Microb Ecol 53: 123-133. 17186148
Protchenko, O., R. Rodriguez-Suarez, R. Androphy, H. Bussey, and C.C. Philpott. (2006). A screen for genes of heme uptake identifies the FLC family required for import of FAD into the endoplasmic reticulum. J. Biol. Chem. 281: 21445-21457. 16717099