Borate Transporters As Models For Studying Slc4 Transport Mechanisms

Borate transport proteins regulate the availability of borate, an essential plant micronutrient that is toxic in excess. Borate transporters share homology with SLC4 transporters, the archetypal member of which 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. In this study we tested whether the S. cerevisiae Bor1 transporter (ScBor1) shares key features in common with the human AE1 transporter (HsAE1) to determine the extent to which ScBor1 serves as a relevant experimental model. Here we show evidence that, like HsAE1, ScBor1 is inhibited by the stilbene derivatives SITS and DIDS. Additionally, we demonstrate that the ScBor1 D347 residue, which is homologous to the essential E681 of HsAE1, can be complemented by the D347E but not D347N substitution. Lastly, we identify several new amino acids critical for function. These data collectively highlight similarities in the biochemical features of ScBor1 and HsAE1 and help elucidate their mechanisms.