Glycoforms of UT-A3 urea transporter with poly-N-acetyllactosamine glycosylation have enhanced transport activity.
Glycoforms of UT-A3 urea transporter with poly-N-acetyllactosamine glycosylation have enhanced transport activity.
复制标题
DOI：
10.1152/ajprenal.00140.2012
复制
发表时间：
2012-07
期刊：
影响因子：
--
通讯作者：
Hua Su;Conner B Carter;O. Fröhlich;R. Cummings;Guangping Chen
中科院分区：
文献类型：
--
作者：
Hua Su;Conner B Carter;O. Fröhlich;R. Cummings;Guangping Chen
尿素转运蛋白UT-A1和UT-A3均表达于肾脏内髓质。然而，UT-A3的功能仍不清楚。在这里，我们发现UT-A3，它只包括UT-A1的NH（2）-末端的一半，在卵母细胞中比UT-A1具有更高的尿素转运活性，这种差异与N-糖基化的差异有关。异源表达的UT-A3被65和45 kDa的两种糖型完全糖基化。相比之下，在HEK 293细胞和卵母细胞中表达的UT-A1仅表现出97-kDa的糖基化形式。我们进一步发现UT-A3的N-聚糖含有大量的聚-N-乙酰乳糖胺。这种高度糖基化的UT-A3更稳定，并且富含细胞膜上的脂筏结构域。Kifunensine是一种α-甘露糖苷酶抑制剂，可抑制高甘露糖型N-聚糖以外的N-聚糖加工，可显著降低UT-A3尿素转运活性。然后，我们检查了来自肾脏内髓质的天然UT-A1和UT-A3糖基化状态，发现UT-A3中65至45 kDa的比例高于UT-A1中117至97 kDa的比例。高糖基化的UT-A3在肾脏内髓细胞膜上的高度稳定表达表明UT-A3可能在尿素重吸收中起重要作用。
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.