N-linked glycosylation is an enzymatic reaction in which an oligosaccharide is transferred en bloc onto an asparagine residue of an acceptor polypeptide, catalyzed by oligosaccharyltransferase (OST). Despite the available crystal structures, the role of the external loop EL5, which is critical for the catalytic cycle, is enigmatic as EL5 in the crystal structures is partially absent or blocks a pathway of lipid-linked oligosaccharide to the active site. Here we report the molecular origin of EL5 conformational changes through a series of molecular dynamics simulations of a bacterial OST, Campylobacter lari PglB. The simulations reveal that the isoprenoid moiety of lipid-linked oligosaccharide favorably binds to a hydrophobic groove of the PglB transmembrane domain. This binding triggers the conformational changes of the transmembrane domain and subsequently impairs the structural stability of EL5, leading to disordered EL5 with open conformations that are required for correct placement of the oligosaccharide in the active site.

中文翻译：

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LLO诱导的PglB跨膜运动与OST活性所需的EL5环构象变化相关

N-联糖基化是一种酶促反应，其中寡糖被寡糖基转移酶（OST）催化整团转移到受体多肽的天冬酰胺残基上。尽管有可用的晶体结构，但对于催化循环至关重要的外环EL5的作用是令人迷惑的，因为晶体结构中的EL5部分不存在或阻止脂质连接的寡糖到达活性位点的途径。在这里，我们通过一系列细菌OST，弯曲弯曲杆菌的分子动力学模拟报告了EL5构象变化的分子起源PglB。模拟显示脂质连接的寡糖的类异戊二烯部分有利地结合到PglB跨膜结构域的疏水槽。这种结合触发了跨膜结构域的构象变化，并随后损害了EL5的结构稳定性，从而导致具有寡聚构象的EL5紊乱，而寡聚构象是正确将寡糖正确放置在活性位点所必需的。