VIPL has sugar-binding activity specific for high-mannose-type N-glycans, and glucosylation of the alpha1,2 mannotriosyl branch blocks its binding |
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Authors: | Yamaguchi Daisuke Kawasaki Norihito Matsuo Ichiro Totani Kiichiro Tozawa Hideto Matsumoto Naoki Ito Yukishige Yamamoto Kazuo |
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Affiliation: | Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience BLD 602, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan. |
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Abstract: | VIP36-like protein (VIPL) was identified as an endoplasmic reticulum (ER) resident protein with homology to VIP36, a cargo receptor involved in the transport of glycoproteins within cells. Although VIPL is structurally similar to VIP36, VIPL is thought not to be a lectin, because its sugar-binding activity has not been detected in several experiments. Here, recombinant soluble VIPL proteins (sVIPL) were expressed in Escherichia coli, biotinylated with biotin ligase and oligomerized with R-phycoerythrin (PE)-labeled streptavidin (SA). As measured with flow cytometry, PE-labeled sVIPL-SA bound to deoxymannojirimycin (DMJ)- or kifunensine (KIF)- but not to swainsonine (SW)-treated HeLaS3 cells in the presence of calcium. A surface plasmon resonance analysis showed that the avidity of sVIPL was enhanced after it formed a complex with SA. The binding of PE-labeled sVIPL-SA was abrogated by endo beta-N-acetylglucosaminidase H treatment of the DMJ- or KIF-treated cells. Competition with several high-mannose-type N-glycans inhibited VIPL binding, and indicated that VIPL recognizes the Manalpha1-2Manalpha1-2Man sequence. Glucosylation of the outer mannose residue of this portion decreased the binding. Although the biochemical characteristics of VIPL are similar to those of VIP36, the sugar-binding activity of VIPL was stronger at neutral pH, corresponding to the pH in the lumen of the ER, than under acidic conditions. |
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Keywords: | high mannose type / lectin / N-glycan / VIPL |
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