Structural Model of the Anion Exchanger 1 (SLC4A1) and Identification of Transmembrane Segments Forming the Transport Site

The anion exchanger 1 (AE1), a member of bicarbonate transporter family SLC4, mediates an electroneutral chloride/bicarbonate exchange in physiological conditions. However, some point mutations in AE1 membrane-spanning domain convert the electroneutral anion exchanger into a Na + and K + conductance or induce a cation leak in a still functional anion exchanger. The molecular determinants that govern ion movement through this transporter are still unknown. The present study was intended to identify the ion translocation pathway within AE1. In the absence of a resolutive three-dimensional structure of AE1 membrane-spanning domain, in silico modeling combined with site-directed mutagenesis experiments was done. A structural model of AE1 membrane-spanning domain is proposed, and this model is based on the structure of a uracil-proton symporter. This model was used to design cysteine-scanning mutagenesis on transmembrane (TM) segments 3 and 5. By measuring AE1 anion exchange activity or cation leak, it is proposed that there is a unique transport site comprising TM3–5 and TM8 that should function as an anion exchanger and a cation leak. Background: There is still no high resolution three-dimensional structure available for the membrane-spanning domain of anion exchanger 1 (AE1). Results: A three-dimensional model of AE1 membrane-spanning domain has been generated in silico and experimentally assessed. Conclusion: Transmembrane segments forming AE1 transport site have been identified. Significance: This is the first three-dimensional model of AE1 membrane-spanning domain based on a cation symporter.