- Glycosylation is important for cell surface expression of the water channel aquaporin-2 but is not essential for tetramerization in the endoplasmic reticulum. Hendriks, G., Koudijs, M., van Balkom, B.W., Oorschot, V., Klumperman, J., Deen, P.M., van der Sluijs, P. J. Biol. Chem. (2004)