The guided entry of tail-anchored proteins (GET) pathway targets C-terminally anchored transmembrane proteins and protects cells from lipotoxicity. Here, we reveal perturbed ergosterol production in ∆get3 cells and demonstrate the sensitivity of GET pathway mutants to the sterol synthesis inhibiting drug terbinafine. Our data uncover a key enzyme of sterol synthesis, the hairpin membrane protein squalene monooxygenase (Erg1), as a non-canonical GET pathway client, thus rationalizing the lipotoxicity phenotypes of GET pathway mutants. Get3 recognizes the hairpin targeting element of Erg1 via its classical client-binding pocket. Intriguingly, we find that the GET pathway is especially important for the acute upregulation of Erg1 induced by low sterol conditions. We further identify several other proteins anchored to the endoplasmic reticulum (ER) membrane exclusively via a hairpin as putative clients of the GET pathway. Our findings emphasize the necessity of dedicated targeting pathways for high-efficiency targeting of particular clients during dynamic cellular adaptation and highlight hairpin proteins as a potential novel class of GET clients.

中文翻译：

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单位发夹膜蛋白 Erg1 的调控靶向需要 GET 途径

尾部锚定蛋白 (GET) 通路的引导进入以 C 端锚定的跨膜蛋白为目标，并保护细胞免受脂毒性。在这里，我们揭示了 Δget3 细胞中麦角甾醇的产生受到干扰，并证明了 GET 途径突变体对甾醇合成抑制药物特比萘芬的敏感性。我们的数据揭示了甾醇合成的关键酶，发夹膜蛋白角鲨烯单加氧酶（Erg1），作为非经典GET途径客户，从而合理化了GET途径突变体的脂毒性表型。Get3 通过其经典的客户端绑定口袋识别 Erg1 的发夹靶向元件。有趣的是，我们发现 GET 途径对于低甾醇条件诱导的 Erg1 急性上调尤其重要。我们进一步鉴定了几种仅通过发夹锚定在内质网（ER）膜上的其他蛋白质，作为 GET 途径的推定客户。我们的研究结果强调了在动态细胞适应过程中高效靶向特定客户的专用靶向途径的必要性，并强调发夹蛋白作为一类潜在的新型 GET 客户。