Band 3 anion transport protein
chloride:bicarbonate antiporter activity
Stomatin modulates the activity of the Anion Exchanger 1 (AE1, SLC4A1).
Anion Exchanger 1 (AE1) and stomatin are integral proteins of the red blood cell (RBC) membrane. Erythroid and kidney AE1 play a major role in HCO<sub>3</sub><sup>-</sup> and Cl<sup>-</sup> exchange. Stomatins down-regulate the activity of many channels and transporters. Biochemical studies suggested an interaction of erythroid AE1 with stomatin. Moreover, we previously reported normal AE1 expression level in stomatin-deficient RBCs. Here, the ability of stomatin to modulate AE1-dependent Cl<sup>-</sup>/HCO<sub>3</sub><sup>-</sup> exchange was evaluated using stopped-flow methods. In HEK293 cells expressing recombinant AE1 and stomatin, the permeabilities associated with AE1 activity were 30% higher in cells overexpressing stomatin, compared to cells with only endogenous stomatin expression. Ghosts from stomatin-deficient RBCs and controls were resealed in the presence of pH- or chloride-sensitive fluorescent probes and submitted to inward HCO<sub>3</sub><sup>-</sup> and outward Cl<sup>-</sup> gradients. From alkalinization rate constants, we deduced a 47% decreased permeability to HCO<sub>3</sub><sup>-</sup> for stomatin-deficient patients. Similarly, kinetics of Cl<sup>-</sup> efflux, followed by the probe dequenching, revealed a significant 42% decrease in patients. In situ Proximity Ligation Assays confirmed an interaction of AE1 with stomatin, in both HEK recombinant cells and RBCs. Here we show that stomatin modulates the transport activity of AE1 through a direct protein-protein interaction.