Shuttling transport receptors carry cargo through nuclear pore complexes (NPCs) via transient interactions with Phe-Gly (FG)-rich nucleoporins. Here, we identify Arx1, a factor associated with a late 60S preribosomal particle in the nucleus, as an unconventional export receptor. Arx1 binds directly to FG nucleoporins and exhibits facilitated translocation through NPCs. Moreover, Arx1 functionally overlaps with the other 60S export receptors, Xpo1 and Mex67-Mtr2, and is genetically linked to nucleoporins. Unexpectedly, Arx1 is structurally unrelated to known shuttling transport receptors but homologous to methionine aminopeptidases (MetAPs), however, without enzymatic activity. Typically, the MetAP fold creates a central cavity that binds the methionine. In contrast, the predicted central cavity of Arx1 is involved in the interaction with FG repeat nucleoporins and 60S subunit export. Thus, an ancient enzyme fold has been adopted by Arx1 to function as a nuclear export receptor.

中文翻译：

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Arx1充当60S核糖体前亚基的非正统核输出受体。

穿梭转运受体通过与富含Phe-Gly（FG）的核孔蛋白的短暂相互作用，通过核孔复合体（NPC）运载货物。在这里，我们将Arx1（一种与细胞核中晚期60S核糖体颗粒相关的因子）识别为非常规出口受体。Arx1直接与FG核孔蛋白结合，并通过NPC表现出易位。此外，Arx1在功能上与其他60S出口受体Xpo1和Mex67-Mtr2重叠，并与核孔蛋白遗传连接。出乎意料的是，Arx1在结构上与已知的穿梭转运受体无关，但与蛋氨酸氨基肽酶（MetAPs）同源，但是没有酶活性。通常，MetAP折叠会形成结合蛋氨酸的中央空腔。相比之下，Arx1的预测中央腔参与与FG重复核孔蛋白和60S亚基输出的相互作用。因此，Arx1已经采用了古老的酶折叠作用来充当核输出受体。