Samal Alexandra B, Green Todd J, Saad Jamil S
Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294.
Proc Natl Acad Sci U S A. 2022 Jun 7;119(23):e2200794119. doi: 10.1073/pnas.2200794119. Epub 2022 Jun 3.
During the late phase of HIV type 1 (HIV-1) infection cycle, the virally encoded Gag polyproteins are targeted to the inner leaflet of the plasma membrane (PM) for assembly, formation of immature particles, and virus release. Gag binding to the PM is mediated by interactions of the N-terminally myristoylated matrix (myrMA) domain with phosphatidylinositol 4,5-bisphosphate. Formation of a myrMA lattice on the PM is an obligatory step for the assembly of immature HIV-1 particles and envelope (Env) incorporation. Atomic details of the myrMA lattice and how it mediates Env incorporation are lacking. Herein, we present the X-ray structure of myrMA at 2.15 Å. The myrMA lattice is arranged as a hexamer of trimers with a central hole, thought to accommodate the C-terminal tail of Env to promote incorporation into virions. The trimer–trimer interactions in the lattice are mediated by the N-terminal loop of one myrMA molecule and α-helices I–II, as well as the 310 helix of a myrMA molecule from an adjacent trimer. We provide evidence that substitution of MA residues Leu13 and Leu31, previously shown to have adverse effects on Env incorporation, induced a conformational change in myrMA, which may destabilize the trimer–trimer interactions within the lattice. We also show that PI(4,5)P2 is capable of binding to alternating sites on MA, consistent with an MA–membrane binding mechanism during assembly of the immature particle and upon maturation. Altogether, these findings advance our understanding of a key mechanism in HIV-1 particle assembly.
在1型人类免疫缺陷病毒（HIV-1）感染周期的后期，病毒编码的Gag多聚蛋白靶向质膜（PM）的内小叶，用于组装、形成未成熟颗粒以及病毒释放。Gag与PM的结合是由N端肉豆蔻酰化的基质（myrMA）结构域与磷脂酰肌醇4,5-二磷酸的相互作用介导的。在PM上形成myrMA晶格是未成熟HIV-1颗粒组装和包膜（Env）掺入的必要步骤。目前尚缺乏myrMA晶格的原子细节及其介导Env掺入的方式。在此，我们展示了分辨率为2.15 Å的myrMA的X射线结构。myrMA晶格排列成具有中心孔的三聚体六聚体，据认为该中心孔可容纳Env的C端尾巴，以促进其掺入病毒粒子。晶格中的三聚体-三聚体相互作用由一个myrMA分子的N端环和α-螺旋I-II以及相邻三聚体中一个myrMA分子的310螺旋介导。我们提供的证据表明，先前已证明对Env掺入有不利影响的MA残基Leu13和Leu31的取代会诱导myrMA的构象变化，这可能会破坏晶格内三聚体-三聚体的相互作用。我们还表明，PI(4,5)P2能够结合到MA上的交替位点，这与未成熟颗粒组装和成熟过程中的MA-膜结合机制一致。总之，这些发现推进了我们对HIV-1颗粒组装关键机制的理解。
