KANADAPTIN IS A PROTEIN THAT INTERACTS WITH THE KIDNEY BUT NOT THE ERYTHROID FORM OF BAND-3

Although epithelial membrane proteins are separately targeted to apica l or basolateral domains, some are apically located in one cell type b ut are basolateral in others. More dramatically, the anion exchanger o f a clonal cell line of intercalated cells derived from the kidney can be retargeted from the apical to basolateral domain. This Cl:HCO3 exc hanger, kAE1, is an alternately spliced form of the erythroid anion ex changer (AE1, band 3), but unlike band 3 it does not bind ankyrin. Her e we identify a new protein (kanadaptin) that binds to the cytoplasmic domain of kAE1 in vitro and in vivo but not to the erythroid AE1 or t o ankyrin. No significant homologous proteins have been reported so fa r. Kanadaptin is widely expressed in epithelial (kidney, lung, and liv er) and non-epithelial cells (brain and skeletal and cardiac muscle). In kidney, we found by immunocytochemistry that kanadaptin was only ex pressed in the collecting tubule. In the intercalated cells of this se gment, it colocalized with k4E1 in cytoplasmic vesicles but not when t he exchanger was in the basolateral membrane. These results raised the possibility that this protein is involved in the targeting of kAE1 ve sicles to their final destination.