NiCoT family
Proteins currently known to belong to the Ni2+-Co2+ Transporter family 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, 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 suggest that it possesses 8 TMSs with its N- and C-termini in the cytoplasm. The Co2+ 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.