Family 2.A.5 - ZIP (ZRT IRT-like Protein Family)       

Family ID: 52616

Members of the ZIP family consist of 220-430 amino acyl residues with eight putative transmembrane spanners. They are derived from animals, plants and yeast, bacteria and archaea. They comprise a diverse family, with several paralogues in any one organism (e.g., twelve in humans, at least five in Caenorhabditis elegans and Arabidopsis thaliana, and two in Saccharomyces cervisiae). The two S. cerevisiae proteins, Zrt1 and Zrt2, both probably transport Zn2+ with high specificity, but Zrt1 transports Zn2+ with ten-fold higher affinity than Zrt2. Some members of the ZIP family have been shown to transport Zn2+ while others transport Fe2+, and at least one transports a range of metal ions. One human protein member of the ZIP family is designated "growth arrest inducible gene product," but its presumed transport activity has not been identified. The energy source for transport has not been characterized, but these systems probably function as secondary carriers. In one study, uptake of Zn2+ via the hZip2 permease was energy independent, independent of Na+ and K+ gradients, but stimulated by HCO3- (Gaither and Eide, 2000). The authors propose a Zn2+:HCO3- symport mechanism. hZip1 is the major Zn2+ uptake system in many human tissues (Gaither and Eide, 2001).