Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 113, Issue 38, Pages 10542-10546Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1612603113
Keywords
X-ray structure; SLC4 transporter; | Bor1; Band 3; membrane protein
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Funding
- University of California Office of the President
- Multicampus Research Programs and Initiatives Grant [MR-15-338599]
- Program for Breakthrough Biomedical Research - Sandler Foundation
- National Institutes of Health [R37 GM024485]
- Alumni Fellow-Life Sciences Research Foundation fellowship
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Boron is essential for plant growth because of its incorporation into plant cellwalls; however, in excess it is toxic to plants. Boron transport and homeostasis in plants is regulated in part by the borate efflux transporter Bor1, a member of the solute carrier (SLC) 4 transporter family with homology to the human bicarbonate transporter Band 3. Here, we present the 4.1-angstrom resolution crystal structure of Arabidopsis thaliana Bor1. The structure displays a dimeric architecture in which dimerization is mediated by centralized Gate domains. Comparisons with a structure of Band 3 in an outward-open state reveal that the Core domains of Bor1 have rotated inwards to achieve an occluded state. Further structural comparisons with UapA, a xanthine transporter from the nucleobase-ascorbate transporter family, show that the downward pivoting of the Core domains relative to the Gate domains may access an inward-open state. These results suggest that the SLC4, SLC26, and nucleobase-ascorbate transporter families all share an elevator transport mechanism in which alternating access is provided by Core domains that carry substrates across a membrane.
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