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The role of N‐glycosylation in the intestinal Cl−/HCO3− exchanger SLC26A3

SLC26A3 is playing major role for Cl− absorption in the intestine. SLC26A3 is expressed in the brush border membrane of the intestinal epithelial cells, which is exposed to very large amounts of protein digestive enzymes. SLC26A3 has extracellular domains, which are exposed to digestive enzymes, and those extracellular domains are important for substrate recognition and functional activity. There are five putative N‐glycosylation sites on the SLC26A3. In the present study, we investigate the role of N‐glycosylation in functional activity and protection against proteolysis. We assessed the expression of SLC26A3 in CHO cells after treatment of an N‐glycosylation inhibitor tunicamycin by immunoblotting and immunofluorescence. Treatment with tunicamycin resulted in SLC26A3 completely unglycosylated but expressed at the plasma membrane. Using these cells we measured the Cl−/HCO3− exchange activity by using BCECF. After the treatment, the rate of pHi increase by removal of extracellular Cl− was attenuated compared to control cells but still robust pHi changes were observed, suggesting that N‐glcosylation of SLC26A3 do not absolutely necessary for Cl−/HCO3− exchange activity. We assessed whether SLC26A3 is protected from proteolytic digestion by trypsin. While the glycosylated SLC26A3 showed little breakdown after treatment with trypsin, deglycosylated SLC26A3 increased susceptibility to trypsin. These results suggest that oligosaccharides protect SLC26A3 from proteolytic digestion.