Function analysis of VIP36 related to protein sorting in intracellular transport

36 kDa囊泡整合蛋白(VIP36)是一种细胞内凝集素，识别含有α-1-→-2甘露糖残基的高甘露糖型糖链。我们从→细胞中分离到高表达的VIP36(+VIP)克隆和突变体VIP36(Asp MVIP Asn)(MVIP)(MVIP)，它们在体外实验中不显示与高甘露糖型多糖结合的活性。在这两个克隆中，VIP36或mVIP36在顶膜中的过度表达大约是在基侧膜中的5倍。在+VIP克隆中，顶端糖蛋白含有的高甘露糖链大约是基侧糖蛋白的四到五倍，与VIP36定位的比例相当。另一方面，mVIP克隆中含有高甘露糖型糖链的糖蛋白被转运到顶端结构域的比例是野生型的两倍，而与mVIP36过表达的比例无关。这些结果表明，VIP36参与了含有高甘露糖型糖链的糖蛋白在细胞内的运输。

The vesicular integral protein of 36 kDa (VIP36) is an intracellular lectin that recognizes high-mannose type glycan containing α1→2 mannose residue. We isolated the overexpressed clones of VIP36 (+VIP) and the mutant VIP36 (Asp→Asn) (mVIP), which did not show binding activities to high-mannose type glycans by in vitro assay, from MDCK cells. In either clone, VIP36 or mVIP36 was overexpressed in the apical membranes about five times more than in the basolateral ones. In the +VIP clone, apical glycoproteins contained high-mannose sugar chains about four to five times more than basolateral glycoproteins corresponding to the relative same ratios as the VIP36 localization. On the other hand, the glycoproteins containing high-mannose type sugar chains in the mVIP clone were transported to the apical domain two times more than to the basolateral domain as wild type, unrelated to the ratios of overexpressed mVIP36. These results indicated that VIP36 was involved in the intracellular transport of glycoproteins containing high-mannose type sugar chains to the final destinations.