Gyimesi, Gergely; Albano, Giuseppe; Fuster, Daniel Guido; Hediger, Matthias A; Pujol Gimenez, Jonai (2019). Unraveling the structural elements of pH sensitivity and substrate binding in the human zinc transporter SLC39A2 (ZIP2). Journal of biological chemistry, 294(20), pp. 8046-8063. American Society for Biochemistry and Molecular Biology 10.1074/jbc.RA118.006113
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J. Biol. Chem.-2019-Gyimesi-8046-63.pdf - Published Version Available under License Creative Commons: Attribution (CC-BY). Download (8MB) | Preview |
The transport and ion-coupling mechanisms of ZIP transporters remain largely uncharacterized. Previous work in our laboratory has revealed that solute carrier family 39 member A2 (SLC39A2/ZIP2) increases its substrate transport rate in the presence of extracellular H Here we used a combination of and techniques involving structural modeling, mutagenesis, and functional characterization in HEK293 cells to identify amino acid residues potentially relevant for both the ZIP2-H interaction and substrate binding. Our ZIP2 models revealed a cluster of charged residues close to the substrate-translocation pore. Interestingly, the H63A substitution completely abrogated pH sensitivity, and substitutions of E67 and F269 altered the pH and voltage modulation of transport. In contrast, substitution of residue E106, which might be part of a dimerization interface, altered pH but not voltage modulation. Substitution of F269, located close to the substrate-binding site, also affected substrate selectivity. These findings were supported by an additional model of ZIP2 that was based on the structure of a prokaryotic homolog, bbZIP, and in silico pK calculations. We also found that residues E179, H175, H202 and E276 are directly involved in the coordination of the substrate metal ion. We noted that, unlike bbZIP, human ZIP2 is predicted to harbor a single divalent metal-binding site, with the charged side-chain of K203 replacing the second bound ion. Our results provide first structural evidence for the previously observed pH and voltage modulation of ZIP2-mediated metal transport, identify the substrate-binding site, and suggest a structure-based transport mechanism for the ZIP2 transporter.
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