title: Glycoforms of UT-A3 urea transporter with poly-N-acetyllactosamine glycosylation have enhanced transport activity.
abstract: Urea transporters UT-A1 and UT-A3 are both expressed in the kidney inner medulla. However, the function of UT-A3 remains unclear. Here, we found that UT-A3, which comprises only the NH(2)-terminal half of UT-A1, has a higher urea transport activity than UT-A1 in the oocyte and that this difference was associated with differences in N-glycosylation. Heterologously expressed UT-A3 is fully glycosylated with two glycoforms of 65 and 45 kDa. By contrast, UT-A1 expressed in HEK293 cells and oocytes exhibits only a 97-kDa glycosylation form. We further found that N-glycans of UT-A3 contain a large amount of poly-N-acetyllactosamine. This highly glycosylated UT-A3 is more stable and is enriched in lipid raft domains on the cell membrane. Kifunensine, an inhibitor of α-mannosidase that inhibits N-glycan processing beyond high-mannose-type N-glycans, significantly reduced UT-A3 urea transport activity. We then examined the native UT-A1 and UT-A3 glycosylation states from kidney inner medulla and found the ratio of 65 to 45 kDa in UT-A3 is higher than that of 117 to 97 kDa in UT-A1. The highly stable expression of highly glycosylated UT-A3 on the cell membrane in kidney inner medulla suggests that UT-A3 may have an important function in urea reabsorption.
authors.affiliation: Renal Division, Emory University School of Medicine, 1639 Pierce Dr., Atlanta, GA 30322, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Su
authors.forename: Conner B
authors.initials: CB
authors.lastname: Carter
authors.forename: Otto
authors.initials: O
authors.lastname: Fröhlich
authors.forename: Richard D
authors.initials: RD
authors.lastname: Cummings
authors.forename: Guangping
authors.initials: G
authors.lastname: Chen
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006031:Glycosylation; D057809:HEK293 Cells; D006801:Humans; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D023421:Models, Animal; D009865:Oocytes / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014162:Transfection; D014508:Urea / Q000378:metabolism*; D014982:Xenopus laevis; D000096982:Urea Transporters
chemical_list: D000470:Alkaloids; D004791:Enzyme Inhibitors; D026901:Membrane Transport Proteins; D011134:Polysaccharides; D014508:Urea; D000096982:Urea Transporters; C065629:kifunensine; C037199:poly-N-acetyllactosamine