| The ZIP and CDF genes are families of metal ion transport proteins characterized in bacteria, yeast, plants, mice, rats, and humans. The ZIP family contains 17 members and the CDF family contains 13 members. Using several sensitive bioinformatic techniques, PSI-BLAST, PSSM, HMM, and threading, we have identified many new members of the ZIP and CDF superfamilies. The new additions to the ZIP family identified by PSI-BLAST, include the gufA and LIV-1 subfamilies as well as several novel human genes, many of which are found in the LIV-1 subfamily. We also identified 96 new members in the CDF superfamily. Key homologous features of the ZIP and CDF proteins were identified using PSSMs and HMMs. These features include the ZIP gene signature sequence located in the carboxy-terminal transmembrane domains IV & V and several highly conserved motifs found in the amino-terminal transmembrane domains of many CDF proteins. These signature sequences and highly conserved motifs are valuable in identifying future members of the families. We also constructed a statistically significant hypothetical three-dimensional model of the hZip1 protein by homology modeling.; From our bioinformatic analysis we identified the human ZIP gene hZIP2. Based on its homology to the ZIP family of eukaryotic metal ion transporters, we hypothesized that it is a zinc transporter. To test whether hZip2 is a zinc transporter, we examined 65Zn uptake activity in transfected K562 erythroleukemia cells expressing hZip2 from the CMV promoter.; After the characterization of hZip2, we were interested in determining what gene or genes controlled endogenous zinc uptake activity in K562 cells. We hypothesized another human ZIP gene, hZIP1, was the endogenous zinc transporter in K562 cells. To test this hypothesis, we examined 65Zn uptake activity in K562 erythroleukemia cells overexpressing hZip1 from the CMV promoter.; In summary, we have isolated and characterized the first two human genes that encode zinc uptake transport proteins. This work has created the molecular tools that can be used to study zinc uptake in humans. The identification of the first human zinc uptake transport proteins will provide the research community with the ability to determine how zinc is taken up in normal and diseased individuals. (Abstract shortened by UMI.);... |
