Envelope glycoprotein mobility on HIV-1 particles depends on the virus maturation state

Jakub Chojnacki,Pablo Carravilla,Dominic Waithe,Nerea Huarte,Christian Eggeling,Jörg Enderlein,Silvia Galiani

doi:10.1038/s41467-017-00515-6

Abstract

Human immunodeficiency virus type 1 (HIV-1) assembles as immature particles, which require the proteolytic cleavage of structural polyprotein Gag and the clustering of envelope glycoprotein Env for infectivity. The details of mechanisms underlying Env clustering remain unknown. Here, we determine molecular dynamics of Env on the surface of individual HIV-1 particles using scanning fluorescence correlation spectroscopy on a super-resolution STED microscope. We find that Env undergoes a maturation-induced increase in mobility, highlighting diffusion as one cause for Env clustering. This mobility increase is dependent on Gag-interacting Env tail but not on changes in viral envelope lipid order. Diffusion of Env and other envelope incorporated proteins in mature HIV-1 is two orders of magnitude slower than in the plasma membrane, indicating that HIV-1 envelope is intrinsically a low mobility environment, mainly due to its general high lipid order. Our results provide insights into dynamic properties of proteins on the surface of individual virus particles.

Highlights

Human immunodeficiency virus type 1 (HIV-1) assembles as immature particles, which require the proteolytic cleavage of structural polyprotein Gag and the clustering of envelope glycoprotein Env for infectivity
Intact HIV-1 virus particles represent a unique highly curved protein/lipid environment whose molecular dynamics have to date not been studied, mainly owing to their small size ( < 140 nm)[3, 10], which is below the resolution limit of conventional optical microscopy
To establish whether sSTED-fluorescence correlation spectroscopy (FCS) is capable of measuring Env mobility on the surface of individual virus particles, we used wild-type mature HIV-1 particles based on the well-described replication incompetent provirus construct pCHIV19

Summary

Introduction

Human immunodeficiency virus type 1 (HIV-1) assembles as immature particles, which require the proteolytic cleavage of structural polyprotein Gag and the clustering of envelope glycoprotein Env for infectivity. Generation of the morphologically mature fully infectious virus particles requires a release of individual proteins (MA (matrix), CA (capsid), NC (nucleocapsid) and p6) from Gag in a series of tightly regulated cleavage steps catalysed by the viral protease (PR) These steps are thought to occur concurrently or shortly after virus particle budding from the plasma membrane of an infected cell, and the entire process, termed maturation, is a crucial step in the HIV-1 replication cycle and an important target in anti-HIV-1 therapy[4]. Despite possessing the same Env protein structure and count as fully mature virus, immature virus particles are non-infectious owing to their inability to enter the target cell[5, 6] This effect appears to be caused by the stiffness of the immature Gag lattice, preventing membrane fusion[7] as well as maturation induced lateral reorganisation of Env[2]. Additional diffusion data of glycophosphatidylinositol (GPI)-anchored proteins as well as major hisocompatibility complex class-I (MHC-I) highlights a generally slow molecular mobility on the viral membrane surface, which is caused by its high degree of lipid order

Methods

Results

Conclusion