Structure of Bor1 supports an elevator transport mechanism for SLC4 anion exchangers.
Boron is essential for plant growth because of its incorporation into plant cell walls; 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-Å 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.
Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158.
Bryan H
BH
Thurtle-Schmidt
Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158 stroud@msg.ucsf.edu.
Robert M
RM
Stroud
D000838:Anions / Q000737:chemistry; D017920:Antiporters / Q000737:chemistry* / Q000378:metabolism; D017360:Arabidopsis / Q000737:chemistry; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism; D001692:Biological Transport / Q000235:genetics; D001895:Boron / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D018360:Crystallography, X-Ray; D004705:Endocytosis / Q000235:genetics; D006801:Humans; D011487:Protein Conformation; D027982:Sodium-Bicarbonate Symporters / Q000737:chemistry* / Q000378:metabolism; D040681:Structural Homology, Protein
D000838:Anions; D017920:Antiporters; D029681:Arabidopsis Proteins; C469216:BOR1 protein, Arabidopsis; C498898:SLC4A4 protein, human; D027982:Sodium-Bicarbonate Symporters; D001895:Boron
Band 3; Bor1; SLC4 transporter; X-ray structure; membrane protein