Structural Insights into the Mechanism of Human T-cell Leukemia Virus Type 1 Gag Targeting to the Plasma Membrane for Assembly

[摘要] Retroviral Gag targeting to the plasma membrane (PM) for assembly is mediated by the N-terminal matrix (MA) domain. For many retroviruses, Gag-PM interaction is dependent on phosphatidylinositol 4,5-bisphosphate (PI(4,5)P-2). However, it has been shown that for human T-cell leukemia virus type 1 (HTLV-1), Gag binding to membranes is less dependent on PI(4,5)P-2 than HIV-1, suggesting that other factors may modulate Gag assembly. To elucidate the mechanism by which HTLV-1 Gag binds to the PM, we employed NMR techniques to determine the structure of unmyristoylated MA (myr(-)MA) and to characterize its interactions with lipids and liposomes. The MA structure consists of four a-helices and unstructured N- and C-termini. We show that myr(-)MA binds to PI(4,5)P-2 via the polar head and that binding to inositol phosphates (IPs) is significantly enhanced by increasing the number of phosphate groups on the inositol ring, indicating that the MA-IP binding is governed by charge-charge interactions. The IP binding site was mapped to a well-defined basic patch formed by lysine and arginine residues. Using an NMR-based liposome binding assay, we show that PI(4,5)P-2 and phosphatidylserine enhance myr(-)MA binding in a synergistic fashion. Confocal microscopy data revealed formation of puncta on the PM of Gag expressing cells. However, G2A-Gag mutant, lacking myristoylation, is diffuse and cytoplasmic. These results suggest that although myr(-)MA binds to membranes, myristoylation appears to be key for formation of HTLV-1 Gag puncta on the PM. Altogether, these findings advance our understanding of a key mechanism in retroviral assembly. (C) 2021 Elsevier Ltd. All rights reserved.

[发布日期] 2021-09-17

[关键词] human T-cell leukemia virus type 1 (HTLV-1);human immunodeficiency virus type 1 (HIV-1);gag myristoylation;Phosphatidylinositol 4;5-bisphosphate (PI(4,5)P-2);nuclear magnetic resonance (NMR)