Program in Cell Biology and 2 Structural Biology Program, Hospital for Sick Children, Toronto, Ontario, Canada M5G1X8.
J Cell Biol. 2009 Nov 30;187(5):701-14. doi: 10.1083/jcb.200909025.
Plasmalemmal phosphatidylinositol (PI) 4,5-bisphosphate (PI4,5P(2)) synthesized by PI 4-phosphate (PI4P) 5-kinase (PIP5K) is key to the polymerization of actin that drives chemotaxis and phagocytosis. We investigated the means whereby PIP5K is targeted to the membrane and its fate during phagosome formation. Homology modeling revealed that all PIP5K isoforms feature a positively charged face. Together with the substrate-binding loop, this polycationic surface is proposed to constitute a coincidence detector that targets PIP5Ks to the plasmalemma. Accordingly, manipulation of the surface charge displaced PIP5Ks from the plasma membrane. During particle engulfment, PIP5Ks detached from forming phagosomes as the surface charge at these sites decreased. Precluding the change in surface charge caused the PIP5Ks to remain associated with the phagosomal cup. Chemically induced retention of PIP5K-gamma prevented the disappearance of PI4,5P(2) and aborted phagosome formation. We conclude that a bistable electrostatic switch mechanism regulates the association/dissociation of PIP5Ks from the membrane during phagocytosis and likely other processes.
质膜磷脂酰肌醇（PI）4,5-二磷酸（PI4,5P(2)）由 PI 4-磷酸（PI4P）5-激酶（PIP5K）合成，是驱动趋化性和吞噬作用的肌动蛋白聚合的关键。我们研究了 PIP5K 靶向质膜的方式及其在吞噬体形成过程中的命运。同源建模揭示了所有 PIP5K 同工型都具有带正电荷的表面。与底物结合环一起，这个多阳离子表面被提议构成一个巧合检测器，将 PIP5K 靶向质膜。因此，表面电荷的操作将 PIP5K 从质膜上置换下来。在颗粒吞噬过程中，随着这些部位表面电荷的减少，PIP5K 从形成的吞噬体中脱离。阻止表面电荷的变化会导致 PIP5K 与吞噬体杯保持关联。化学诱导的 PIP5K-γ保留阻止了 PI4,5P(2)的消失，并中断了吞噬体的形成。我们得出结论，双稳态静电开关机制调节了吞噬过程中和其他过程中 PIP5K 与膜的结合/解离。
