ROLE OF N-GLYCOSYLATION IN THE EXPRESSION OF HUMAN BAND 3-MEDIATED ANION TRANSPORT

The human erythrocyte anion transporter (band 3; AE1) has a single N l inked glycosylation site at amino residue Asn-642. To investigate the functional role of the N-glycan in band 3 (b3) we have constructed mut ant b3 cDNAs in which this residue has been replaced by Gly, Ser or Th r, and the expression of these mutants was examined in Xenopus oocytes . Chymotrypsin treatment of intact oocytes was used to assess surface b3. Similar amounts of cleavage were observed with both glycosylated a nd unglycosylated b3. Greater cleavage of b3 was obtained when human r ed cell glycophorin A (GPA) was cc-expressed with either glycosylated or unglycosylated b3. The co-expression of GPA with either glycosylate d or unglycosylated b3 increased the stilbene disulphonate-sensitive c hloride transport into oocytes at low cRNA concentrations. In both the presence or absence of GPA, a higher b3-mediated chloride influx into oocytes was observed on expression of glycosylated b3 cRNA compared w ith similar amounts of unglycosylated b3 cRNA. We suggest that glycosy lation is not essential for the expression of functional b3 in oocytes , but may play a role in enabling the protein to acquire its correct f olding with the highest anion transport activity.