Role of malectin in Glc(2)Man(9)GlcNAc(2)-dependent quality control of α1-antitrypsin.
Role of malectin in Glc(2)Man(9)GlcNAc(2)-dependent quality control of α1-antitrypsin.
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DOI：
10.1091/mbc.e11-03-0201
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发表时间：
2011-10
影响因子：
3.3
通讯作者：
Yamamoto K
中科院分区：
文献类型：
--
作者：
Chen Y;Hu D;Yabe R;Tateno H;Qin SY;Matsumoto N;Hirabayashi J;Yamamoto K
在细胞中，人malectin通过G2 M9聚糖与新合成的ATNHK稳定相互作用，但不与AT相互作用。ATNHK与malectin的相互作用导致ATNHK的ERAD增强，并阻止错误折叠的糖蛋白的分泌。这些发现提供了malectin通过识别G2 M9在糖蛋白质量控制中的作用的证据。马来凝集素是从非洲爪蟾中发现的一种新的内质网凝集素，与细菌糖基水解酶具有相似的结构。与其他参与糖蛋白质量控制的细胞内凝集素一样，malectin在动物中高度保守。体外膜结合试验和正面亲和色谱的结果证实，人malectin与Glc 2 Man 9 GlcNAc 2（G2 M9）N-聚糖特异性结合，Ka为1.97 × 105 M−1，而与Glc 1 Man 9 GlcNAc 2（G1 M9）、Glc 3 Man 9 GlcNAc 2（G3 M9）和其他N-聚糖的结合几乎不可检测。代谢标记和免疫沉淀实验表明，在进入钙连接蛋白循环之前，折叠缺陷的人α1-抗胰蛋白酶变体null Hong Kong（ATNHK）稳定地与malectin结合，而野生型α1-抗胰蛋白酶（AT）或ATNHK的N-聚糖截短变体（ATNHK-Q3）不与malectin结合。此外，malectin过表达通过涉及增强ER相关蛋白降解的机制显著抑制ATNHK的分泌;相比之下，AT和ATNHK-Q3的分泌仅受malectin过表达的轻微影响。衣霉素诱导的内质网应激导致malectin mRNA转录显著升高。这些观察结果表明，通过G2 M9识别，malectin在调节新合成的糖蛋白中可能起作用。
In cells, human malectin stably interacted with newly synthesized ATNHK, but not AT, via G2M9 glycans. The interaction of ATNHK with malectin resulted in enhanced ERAD of ATNHK and prevented the secretion of the misfolded glycoprotein. These findings provide evidence of a role of malectin in glycoprotein quality control via recognition of G2M9. Malectin was first discovered as a novel endoplasmic reticulum (ER)–resident lectin from Xenopus laevis that exhibits structural similarity to bacterial glycosylhydrolases. Like other intracellular lectins involved in glycoprotein quality control, malectin is highly conserved in animals. Here results from in vitro membrane-based binding assays and frontal affinity chromatography confirm that human malectin binds specifically to Glc2Man9GlcNAc2 (G2M9) N-glycan, with a Ka of 1.97 × 105 M−1, whereas binding to Glc1Man9GlcNAc2 (G1M9), Glc3Man9GlcNAc2 (G3M9), and other N-glycans is barely detectable. Metabolic labeling and immunoprecipitation experiments demonstrate that before entering the calnexin cycle, the folding-defective human α1-antitrypsin variant null Hong Kong (ATNHK) stably associates with malectin, whereas wild-type α1-antitrypsin (AT) or N-glycan–truncated variant of ATNHK (ATNHK-Q3) dose not. Moreover, malectin overexpression dramatically inhibits the secretion of ATNHK through a mechanism that involves enhanced ER-associated protein degradation; by comparison, the secretion of AT and ATNHK-Q3 is only slightly affected by malectin overexpression. ER-stress induced by tunicamycin results in significantly elevated mRNA transcription of malectin. These observations suggest a possible role of malectin in regulating newly synthesized glycoproteins via G2M9 recognition.