Coat protein complex II (COPII) proteins form vesicles from the endoplasmic reticulum to export cargo molecules to the Golgi apparatus. Among the many proteins involved in this process, Sec12 is a key regulator, functioning as the guanosine diphosphate (GDP) exchange factor for Sar1p, the small guanosine triphosphatase (GTPase) that initiates COPII assembly. Here we show that overexpression of phospholipase B3 in the thermosensitive sec12-4 mutant partially restores growth and protein transport at non-permissive temperatures. Lipidomics analyses of these cells show a higher content of lysophosphatidylinositol (lysoPI), consistent with the lipid specificity of PLB3. Furthermore, we show that lysoPI is specifically enriched in COPII vesicles isolated from in vitro budding assays. As these results suggested that lysophospholipids could facilitate budding under conditions of defective COPII coat dynamics, we reconstituted COPII binding onto giant liposomes with purified proteins and showed that lysoPI decreases membrane rigidity and enhances COPII recruitment to liposomes. Our results support a mechanical facilitation of COPII budding by lysophospholipids.

外壳蛋白复合物II（COPII）蛋白从内质网形成囊泡，以将货物分子输出到高尔基体。在此过程涉及的许多蛋白质中，Sec12是关键调节剂，充当Sar1p的鸟苷二磷酸（GDP）交换因子，Sar1p是引发COPII组装的小鸟苷三磷酸酶（GTPase）。在这里，我们显示在热敏sec12-4突变体中磷脂酶B3的过表达部分恢复了在非允许温度下的生长和蛋白质运输。这些细胞的脂质组学分析显示较高的溶血磷脂酰肌醇（lysoPI）含量，与PLB3的脂质特异性一致。此外，我们显示了lysoPI在从体外分离的COPII囊泡中特别富集出芽测定。由于这些结果表明，在有缺陷的COPII涂层动力学条件下，溶血磷脂可以促进出芽，我们用纯化的蛋白将COPII结合到巨型脂质体上，并显示lysoPI降低了膜的刚性，并增强了COPII募集到脂质体的能力。我们的结果支持溶血磷脂对COPII萌芽的机械促进。