Kajiura Hiroyuki, Eguchi Takanori, Uchino Keiro, Tatematsu Ken-Ichiro, Tamura Toshiki, Sezutsu Hideki, Fujiyama Kazuhito
International Center for Biotechnology, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan; Institute for Open and Transdisciplinary Research Initiatives (OTRI), Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
International Center for Biotechnology, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
J Biosci Bioeng. 2022 Jun;133(6):533-540. doi: 10.1016/j.jbiosc.2022.03.001. Epub 2022 Apr 6.
N-glycosylation of proteins is an important post-translational modification in eukaryotic cells. One of the key modifications in protein N-glycosylation is N-acetylglucosamine (GlcNAc) extension mediated by N-acetylglucosaminyltransferase I (GNTI), which triggers N-glycan maturation from high-mannose-type to hybrid- and complex-type structures in Golgi. However, the temporal contributions of GNTI to GlcNAc extension and the resultant N-glycan structures in insects have not been analyzed. Here, focusing on GlcNAc extension of N-glycan in the silkworm Bombyx mori, we analyzed the temporal N-glycan alterations in the middle silk gland (MSG) and characterized the property of key enzyme for complex-type N-glycan biosynthesis, B. mori GNTI (BmGNTI). N-glycan analysis of N-glycoproteins in the MSG demonstrated that BmGNTI identified and characterized in this study consistently contributed to GlcNAc extension of N-glycans, which led to the accumulation of GlcNAc-extended N-glycans as predominant structures throughout the MSG development. The expression profile of GlcNAc extension-related genes revealed that the enzymes contributing to the hydrolysis of GlcNAc showed stage-specific expressions, thereby resulting in accumulations of the end product N-glycans of the enzyme. These results lead to the speculation that not BmGNTI but rather glycosylhydrolases critically influenced the structural formations and the changes in the ratio of N-glycans with GlcNAc residue(s) in MSG.
蛋白质的N-糖基化是真核细胞中一种重要的翻译后修饰。蛋白质N-糖基化的关键修饰之一是由N-乙酰葡糖胺转移酶I（GNTI）介导的N-乙酰葡糖胺（GlcNAc）延伸，它触发了高尔基体中N-聚糖从高甘露糖型向杂合型和复合型结构的成熟。然而，尚未分析GNTI在昆虫中对GlcNAc延伸和由此产生的N-聚糖结构的时间贡献。在这里，我们以家蚕中丝腺（MSG）中N-聚糖的GlcNAc延伸为重点，分析了其中N-聚糖的时间变化，并对复合型N-聚糖生物合成关键酶家蚕GNTI（BmGNTI）的特性进行了表征。对MSG中N-糖蛋白的N-聚糖分析表明，本研究中鉴定和表征的BmGNTI持续促进了N-聚糖的GlcNAc延伸，这导致在整个MSG发育过程中，GlcNAc延伸的N-聚糖作为主要结构积累。GlcNAc延伸相关基因的表达谱显示，参与GlcNAc水解的酶呈现阶段特异性表达，从而导致该酶的终产物N-聚糖积累。这些结果引发了这样的推测：在MSG中，对具有GlcNAc残基的N-聚糖的结构形成和比例变化起关键影响作用的不是BmGNTI，而是糖基水解酶。
