Cryo-EM structures of human ZnT8 in both outward- and inward-facing conformations
- University of Texas Southwestern Medical Center, United States
Abstract
ZnT8 is a Zn2+/H+ antiporter that belongs to SLC30 family and plays an essential role in regulating Zn2+ accumulation in the insulin secretory granules of pancreatic β cells. Dysfunction of ZnT8 is associated with both type 1 and 2 diabetes. However, the Zn2+/H+ exchange mechanism of ZnT8 remains unclear due to the lack of high-resolution structures. Here, we report the cryo-EM structures of human ZnT8 (HsZnT8) in both outward- and inward-facing conformations. HsZnT8 forms a dimeric structure with four Zn2+ binding sites within each subunit: a highly conserved primary site in transmembrane domain (TMD) housing the Zn2+ substrate; an interfacial site between TMD and C-terminal domain (CTD) that modulates the Zn2+ transport activity of HsZnT8; and two adjacent sites buried in the cytosolic domain and chelated by conserved residues from CTD and the His-Cys-His (HCH) motif from the N-terminal segment of the neighboring subunit. A comparison of the outward- and inward-facing structures reveals that the TMD of each HsZnT8 subunit undergoes a large structural rearrangement, allowing for alternating access to the primary Zn2+ site during the transport cycle. Collectively, our studies provide the structural insights into the Zn2+/H+ exchange mechanism of HsZnT8.
Data availability
The Cryo-EM maps of HsZnT8 determined in three different conditions will have been deposited in the Electron Microscopy Data Bank and. The corresponding atomic coordinates will be deposited to the RCSB Protein Data Bank, with the entry ID: EMD-22285 and PDB 6XPD for the structure of HsZnT8-DM, EMD-22286 and PDB 6XPE for the structure of HsZnT8-WT in the presence of zinc, and EMD-22287 and PDB 6XPF for the structure of HsZnT8-WT in the absence of zinc. Source data files have been provided for Figure 2h and 2i.
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Structural basis for the autoregulation of the zinc transporter YiiPElectron Microscopy Data Bank, 3h90.
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CryoEM Structure of the Zinc Transporter YiiP from helical crystalsElectron Microscopy Data Bank, 5vrf.
Article and author information
Author details
Funding
National Institute of General Medical Sciences (R01GM136976)
- Xiao-chen Bai
Welch Foundation (I-1944)
- Xiao-chen Bai
Cancer Prevention and Research Institute of Texas (RP160082)
- Xiao-chen Bai
Howard Hughes Medical Institute
- Youxing Jiang
National Institute of General Medical Sciences (GM079179)
- Youxing Jiang
Welch Foundation (I-1578)
- Youxing Jiang
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2020, Xue et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Cryo-EM structures of human ZnT8 in both outward- and inward-facing conformations
eLife 9:e58823.
https://doi.org/10.7554/eLife.58823
