title: NiCoT family
text: # NiCoT family
  
  Proteins currently known to belong to the $Ni^{2+}-Co^{2+}$ 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 $Ni^{2+}$ and/or $Co^{2+}$ 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 $Ni^{2+}$ transporter of Ralstonia eutropha (Alcaligenes eutrophus) suggest that it possesses 8 TMSs with its N- and C-termini in the cytoplasm. The $Co^{2+}$ $(Ni^{2+})$ 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 $HX^4DH$ motif in helix 2 of the HoxN protein has been implicated in $Ni^{2+}$ 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 $Ni^{2+}$ 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:
  
         $[Ni^{2+}$ and/or $Co^{2+}]$ (out) → $[Ni^{2+}$ and/or $Co^{2+}]$ (in).
  
  ## Proteins
  
  Several characterized proteins belong to the $Ni^{2+}-Co^{2+}$ 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.
  
  