Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Proc Natl Acad Sci U S A. 2013 Feb 26;110(9):3525-30. doi: 10.1073/pnas.1216655110. Epub 2013 Feb 11.
Localization of the HIV type-1 (HIV-1) Gag protein on the plasma membrane (PM) for virus assembly is mediated by specific interactions between the N-terminal myristoylated matrix (MA) domain and phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P(2)]. The PM bilayer is highly asymmetric, and this asymmetry is considered crucial in cell function. In a typical mammalian cell, the inner leaflet of the PM is enriched in phosphatidylserine (PS) and phosphatidylethanolamine (PE) and contains minor populations of phosphatidylcholine (PC) and PI(4,5)P(2). There is strong evidence that efficient binding of HIV-1 Gag to membranes is sensitive not only to lipid composition and net negative charge, but also to the hydrophobic character of the acyl chains. Here, we show that PS, PE, and PC interact directly with MA via a region that is distinct from the PI(4,5)P(2) binding site. Our NMR data also show that the myristoyl group is readily exposed when MA is bound to micelles or bicelles. Strikingly, our structural data reveal a unique binding mode by which the 2'-acyl chain of PS, PE, and PC lipids is buried in a hydrophobic pocket whereas the 1'-acyl chain is exposed. Sphingomyelin, a major lipid localized exclusively on the outer layer of the PM, does not bind to MA. Our findings led us to propose a trio engagement model by which HIV-1 Gag is anchored to the PM via the 1'-acyl chains of PI(4,5)P(2) and PS/PE/PC and the myristoyl group, which collectively bracket a basic patch projecting toward the polar leaflet of the membrane.
HIV-1（人类免疫缺陷病毒 1 型）Gag 蛋白在质膜（PM）上的定位对于病毒组装是由 N 端豆蔻酰化基质（MA）结构域与磷脂酰肌醇-（4,5）-二磷酸[PI（4,5）P（2）]之间的特定相互作用介导的。PM 双层具有高度的不对称性，这种不对称性被认为对细胞功能至关重要。在典型的哺乳动物细胞中，PM 的内叶富含磷脂酰丝氨酸（PS）和磷脂酰乙醇胺（PE），并含有少量的磷脂酰胆碱（PC）和 PI（4,5）P（2）。有强有力的证据表明，HIV-1 Gag 与膜的有效结合不仅对脂质组成和净负电荷敏感，而且对酰基链的疏水性敏感。在这里，我们表明 PS、PE 和 PC 通过与 MA 结合的一个与 PI（4,5）P（2）结合位点不同的区域直接与 MA 相互作用。我们的 NMR 数据还表明，当 MA 与胶束或双胶束结合时，豆蔻酰基很容易暴露。引人注目的是，我们的结构数据揭示了一种独特的结合模式，其中 PS、PE 和 PC 脂质的 2'-酰基链被埋藏在疏水性口袋中，而 1'-酰基链则暴露在外。神经鞘磷脂是一种主要位于 PM 外层的脂质，它不与 MA 结合。我们的发现使我们提出了一个三重结合模型，通过该模型，HIV-1 Gag 通过 PI（4,5）P（2）和 PS/PE/PC 的 1'-酰基链以及豆蔻酰基锚定在 PM 上，这些基团共同构成了一个朝向膜极性叶的碱性斑。
