The Conserved Tyr176/Leu177 Motif in the α-Helix 9 of the Feline Immunodeficiency Virus Capsid Protein Is Critical for Gag Particle Assembly

César A Ovejero,Silvia A González,José L Affranchino

doi:10.3390/v11090816

César A Ovejero, Silvia A González + Show 1 more

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https://doi.org/10.3390/v11090816

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Abstract

The capsid domain (CA) of the lentiviral Gag polyproteins has two distinct roles during virion morphogenesis. As a domain of Gag, it mediates the Gag–Gag interactions that drive immature particle assembly, whereas as a mature protein, it self-assembles into the conical core of the mature virion. Lentiviral CA proteins are composed of an N-terminal region with seven α-helices and a C-terminal domain (CA-CTD) formed by four α-helices. Structural studies performed in HIV-1 indicate that the CA-CTD helix 9 establishes homodimeric interactions that contribute to the formation of the hexameric Gag lattice in immature virions. Interestingly, the mature CA core also shows inter-hexameric associations involving helix 9 residues W184 and M185. The CA proteins of feline immunodeficiency virus (FIV) and equine infectious anemia virus (EIAV) exhibit, at equivalent positions in helix 9, the motifs Y176/L177 and L169/F170, respectively. In this paper, we investigated the relevance of the Y176/L177 motif for FIV assembly by introducing a series of amino acid substitutions into this sequence and studying their effect on in vivo and in vitro Gag assembly, CA oligomerization, mature virion production, and viral infectivity. Our results demonstrate that the Y176/L177 motif in FIV CA helix 9 is essential for Gag assembly and CA oligomerization. Notably, mutations converting the FIV CA Y176/L177 motif into the HIV-1 WM and EIAV FL sequences allow substantial particle production and viral replication in feline cells.

Highlights

Feline immunodeficiency virus (FIV), like all other lentiviruses, assembles at the plasma membrane of the infected cells [1]
Fitting the high-resolution structure of the HIV-1 capsid domain (CA)-CTD into intact immature virions showed that helix 9 forms a homodimeric interface linking neighboring hexamers, and that the CA residues W184 and M185 are critical for this interface interaction [20]
The 1.67 Å crystal structure of the feline immunodeficiency virus (FIV) CA has recently been determined (Figure 1A) [33] and, the linker connecting the CA-NTD and CA-CTD is shorter than those found in the HIV-1 and equine infectious anemia virus (EIAV) CA proteins [31,51], the FIV CA-NTD and CA-CTD can still be individually superposed with those of HIV-1 and EIAV [33]

Summary

Introduction

Feline immunodeficiency virus (FIV), like all other lentiviruses, assembles at the plasma membrane of the infected cells [1]. The viral Gag polyprotein multimerizes into immature virions that bud into the extracellular medium [1] In this regard, we have previously demonstrated that the FIV Gag precursor, when expressed in mammalian cells in the absence of other viral proteins, assembles into virus-like particles (VLPs) morphologically similar to immature virions [2]. The Gag polyproteins of human and simian immunodeficiency viruses (HIV-1 and SIV, respectively) can assemble into VLPs both in vivo and in vitro [4,5,6,7,8,9,10] Taken together, these observations underscore the notion that lentiviral Gag polyproteins contain all the molecular determinants necessary for virion assembly and budding [11,12]

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