Borate Transporters Are Inhibited by the Stilbene‐Derived Inhibitor SITS

Abstract

Borate transport proteins regulate the availability of borate, an essential plant micronutrient that is toxic in excess. Borate transporters in plants and fungi share sequence and structural homology with the SLC4 transporters, which suggests they might share other key features. The archetypal member of SLC4 transporters is human Band 3, or Anion Exchanger 1 (AE1). AE1 is the most abundant membrane protein in red blood cells where it exchanges bicarbonate and chloride, and mutations in AE1 are linked to several diseases such as hereditary spherocytosis and renal tubular acidosis. We tested whether the S. cerevisiae Bor1 (ScBor1) and A. thaliana Bor4 (AtBor4) transporters share with human AE1 (HsAE1) a sensitivity to inhibitors derived from stilbene. We show that ScBor1 and AtBor4 are both specifically inhibited by SITS, a known inhibitor of HsAE1. We also demonstrate that a poorly conserved N‐terminal region in ScBor1 can be deleted without impeding ScBor1 function in vivo, establishing a common functional core between borate transporters and the membrane transport domains of SLC4 transporters. Lastly, we show that the N‐terminal tail does not contribute to oxidative crosslinking in lipid‐mediated dimerization, which is surprising given a recent structural prediction from the AlphaFold server. These results collectively show important similarities between plant and fungal borate transporters and HsAE1 and demonstrate that borate transporter similarities with SLC4 transporters extend beyond sequence and structure. Further studies will be required to establish the amino acids most responsible for dimerization in SLC4 transporters and their homologs.