NiCoT family

Proteins currently known to belong to the Ni²⁺-Co²⁺ Transporter (NiCoT) family (TC# 2.A.52) can be found in organisms ranging from Gram-negative and Gram-positive bacteria to archaea and some eukaryotes. Members of this family catalyze uptake of Ni²⁺ and/or Co²⁺ in a proton motive force-dependent process.

Structure

These proteins range in size from about 300 to 400 amino acyl residues and possess 6, 7, or 8 transmembrane segments (TMSs), thought to result from an intragenic 4 TMS duplication, followed by a deletion of one or two TMSs in the cases of the 7 or 6 TMS proteins. Topological analyses with the HoxN Ni²⁺ transporter of Ralstonia eutropha (Alcaligenes eutrophus) suggest that it possesses 8 TMSs with its N- and C-termini in the cytoplasm. The Co²⁺ (Ni²⁺) transporter of Rhodococcus rhodochrous, NhlF, exhibits eight putative TMSs, and eight apparent TMSs are revealed by hydropathy analyses of multiple alignments of family protein sequences. An HX⁴DH motif in helix 2 of the HoxN protein has been implicated in Ni²⁺ binding, and both helix 1 and helix 2, which interact spatially, form the selectivity filter. In the Helicobacter pylori NixA homologue, several conserved motifs have been shown to be important for Ni²⁺ binding and transport.

At least one crystal structure is known, determined by Yu et al., available at PDB: 4M58​.

Reaction

The overall reaction catalyzed by the proteins of the NiCoT family is:

[Ni²⁺ and/or Co²⁺] (out) → [Ni²⁺ and/or Co²⁺] (in).

Proteins

Several characterized proteins belong to the Ni²⁺-Co²⁺ Transporter (NiCoT) Family (TC# 2.A.43). A complete list of these proteins along with their transporter classification identification numbers (TCID), domain, kingdom/phylum, and some examples can be found in the Transporter Classification Database.

Further reading

• Deng, X; He, J; He, N (February 2013). "Comparative study on Ni(2+)-affinity transport of nickel/cobalt permeases (NiCoTs) and the potential of recombinant Escherichia coli for Ni(2+) bioaccumulation". Bioresour. Technol. 130: 69–74. doi:10.1016/j.biortech.2012.11.133. PMID 23306112.
• Rodionov, D; Hebbeln, P; Gelfand, M; Eitinger, T (January 2006). "Comparative and Functional Genomic Analysis of Prokaryotic Nickel and Cobalt Uptake Transporters: Evidence for a Novel Group of ATP-Binding Cassette Transporters". J. Bacteriol. 188 (1): 317–327. doi:10.1128/JB.188.1.317-327.2006. PMC 1317602. PMID 16352848.