近日，瑞士苏黎世联邦理工学院Kaspar P. Locher研究组解析出人寡糖转移酶复合物OST-A和OST-B的冷冻电镜结构。相关论文发表在2019年12月13日出版的《科学》上。

研究人员表示，寡糖转移酶（OST）催化高甘露糖聚糖转移到内质网的分泌蛋白上。 哺乳动物表达两种不同的OST复合物，它们以共翻译（OST-A）或转录后（OST-B）的方式起作用。

研究人员报道了人类OST-A和OST-B的高分辨率冷冻电镜结构。 尽管它们具有相似的总体架构，但催化亚基STT3A和STT3B的结构差异促进了与不同OST亚基，OST-A中的DC2和OST-B中的MAGT1的接触。在OST-A中，与TMEM258和STT3A的相互作用使核糖蛋白I形成可以结合翻译核糖体的四螺旋束，而OST-B中的等效区域是无序的。研究人员观察到一个受体肽和磷酸二氢磷酸酯与STT3B结合，但在STT3A中只有磷酸二氢磷酸酯，表明这两种OST复合物对蛋白质底物的独特亲和力。

附：英文原文

Title: Cryo–electron microscopy structures of human oligosaccharyltransferase complexes OST-A and OST-B

Author: Ana S. Ramírez, Julia Kowal, Kaspar P. Locher

Issue&Volume: 2019/12/13

Abstract: Oligosaccharyltransferase (OST) catalyzes the transfer of a high-mannose glycan onto secretory proteins in the endoplasmic reticulum. Mammals express two distinct OST complexes that act in a cotranslational (OST-A) or posttranslocational (OST-B) manner. Here, we present high-resolution cryo–electron microscopy structures of human OST-A and OST-B. Although they have similar overall architectures, structural differences in the catalytic subunits STT3A and STT3B facilitate contacts to distinct OST subunits, DC2 in OST-A and MAGT1 in OST-B. In OST-A, interactions with TMEM258 and STT3A allow ribophorin-I to form a four-helix bundle that can bind to a translating ribosome, whereas the equivalent region is disordered in OST-B. We observed an acceptor peptide and dolichylphosphate bound to STT3B, but only dolichylphosphate in STT3A, suggesting distinct affinities of the two OST complexes for protein substrates.

DOI: 10.1126/science.aaz3505

Source:https://science.sciencemag.org/content/366/6471/1372