在巨自噬期间,细胞质成分被自噬体吞噬。溶酶体与封闭的自噬体融合,但不与未封闭的中间结构融合。这在一定程度上是通过将自噬体SNARE突触蛋白17(STX17)晚期募集到成熟的自噬体来实现的。然而,STX17如何识别自噬体成熟尚不清楚。这里,我们表明,STX17的这种时间调节的募集取决于STX17的带正电荷的C末端区域。与这一发现一致,成熟的自噬体与未封闭的中间结构相比带负电。自噬体的静电成熟可能是由自噬体膜中磷脂酰肌醇4-磷酸(PI4P)的积累驱动的。因此,自噬体PI4P的去磷酸化阻止了STX17与自噬体的关联。此外,分子动力学模拟支持STX17跨膜螺旋的PI4P依赖性膜插入。基于这些发现,我们提出了一个模型,在该模型中,成熟自噬体的STX17募集受到PI4P驱动的自噬体表面电荷变化的时间调控.
During macroautophagy, cytoplasmic constituents are engulfed by autophagosomes. Lysosomes fuse with closed autophagosomes but not with unclosed intermediate structures. This is achieved in part by the late recruitment of the autophagosomal SNARE syntaxin 17 (STX17) to mature autophagosomes. However, how STX17 recognizes autophagosome maturation is not known. Here, we show that this temporally regulated recruitment of STX17 depends on the positively charged C-terminal region of STX17. Consistent with this finding, mature autophagosomes are more negatively charged compared with unclosed intermediate structures. This electrostatic maturation of autophagosomes is likely driven by the accumulation of phosphatidylinositol 4-phosphate (PI4P) in the autophagosomal membrane. Accordingly, dephosphorylation of autophagosomal PI4P prevents the association of STX17 to autophagosomes. Furthermore, molecular dynamics simulations support PI4P-dependent membrane insertion of the transmembrane helices of STX17. Based on these findings, we propose a model in which STX17 recruitment to mature autophagosomes is temporally regulated by a PI4P-driven change in the surface charge of autophagosomes.