Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6JJ, United Kingdom.
J Biol Chem. 2012 Sep 14;287(38):32263-76. doi: 10.1074/jbc.M112.375840. Epub 2012 Jul 21.
Phosphatidylinositol transfer proteins (PITPs) are versatile proteins required for signal transduction and membrane traffic. The best characterized mammalian PITPs are the Class I PITPs, PITPα (PITPNA) and PITPβ (PITPNB), which are single domain proteins with a hydrophobic cavity that binds a phosphatidylinositol (PI) or phosphatidylcholine molecule. In this study, we report the lipid binding properties of an uncharacterized soluble PITP, phosphatidylinositol transfer protein, cytoplasmic 1 (PITPNC1) (alternative name, RdgBβ), of the Class II family. We show that the lipid binding properties of this protein are distinct to Class I PITPs because, besides PI, RdgBβ binds and transfers phosphatidic acid (PA) but hardly binds phosphatidylcholine. RdgBβ when purified from Escherichia coli is preloaded with PA and phosphatidylglycerol. When RdgBβ was incubated with permeabilized HL60 cells, phosphatidylglycerol was released, and PA and PI were now incorporated into RdgBβ. After an increase in PA levels following activation of endogenous phospholipase D or after addition of bacterial phospholipase D, binding of PA to RdgBβ was greater at the expense of PI binding. We propose that RdgBβ, when containing PA, regulates an effector protein or can facilitate lipid transfer between membrane compartments.
磷脂酰肌醇转移蛋白（PITPs）是一类多功能蛋白，在信号转导和膜运输中发挥重要作用。目前研究最为深入的哺乳动物 PITPs 是 I 类 PITPs，包括 PITPα（PITPNA）和 PITPβ（PITPNB），它们均为具有疏水性腔的单结构域蛋白，能够结合一个磷酸肌醇（PI）或磷酸胆碱分子。在本研究中，我们报道了 II 类家族中一种尚未鉴定的可溶性 PITP，即磷脂酰肌醇转移蛋白，细胞质 1（PITPNC1）（别名，RdgBβ）的脂质结合特性。我们发现该蛋白的脂质结合特性与 I 类 PITPs 不同，因为除了 PI 之外，RdgBβ还能够结合和转运磷脂酸（PA），但几乎不结合磷脂酰胆碱。RdgBβ 从大肠杆菌中纯化出来时就预先装载了 PA 和磷脂酰甘油。当 RdgBβ 与通透的 HL60 细胞孵育时，会释放出磷脂酰甘油，此时 PA 和 PI 被掺入 RdgBβ。在激活内源性磷脂酶 D 或添加细菌磷脂酶 D 导致 PA 水平增加后，PA 与 RdgBβ 的结合增加，PI 结合减少。我们推测，当 RdgBβ 含有 PA 时，它可以调节效应蛋白，或者促进膜隔间之间的脂质转移。
