The GTPase Domain of MX2 Interacts with HIV-1 Capsid Enabling Its Short Isoform to Moderate Antiviral Restriction

Gilberto Betancor,Apolonia L,Michael H Malim,Nabil H Ali,Matthew Dj Dicks,Jose M Jimenez-&Shy;Guarde&Ntilde;O

doi:10.2139/ssrn.3376665

Abstract

Myxovirus resistance 2 (MX2/MXB) is an interferon (IFN)-induced HIV-1 restriction factor that inhibits viral nuclear DNA accumulation. The amino-terminal domain of MX2 binds the viral capsid and is essential for inhibition. Using in vitro assembled Capsid-Nucleocapsid (CANC) complexes as a surrogate for the HIV-1 capsid lattice, we reveal that the GTPase (G) domain of MX2 contains a second, independent capsid binding site. The importance of this interaction was addressed in a series of competition assays using the naturally occurring non-antiviral short isoform of MX2 that lacks the amino-terminal 25 amino acids. Specifically, we show that the G domain enhances MX2 function, and that the foreshortened isoform acts as a functional suppressor of the full-length protein in a G domain-dependent manner. The interaction of MX2 with its HIV-1 capsid substrate is therefore multi-faceted: there are dual points of contact which, together with protein oligomerization, contribute to the complexity of MX2 regulation.

Highlights

Upon viral infection, activation of the innate immune response mobilizes an antiviral state
CPSF6 was readily detected in the pellet fraction when CANC complexes were present, but not when they were absent, and GFP failed to interact with these complexes (Figure 1A)
Further confirmation of this finding was obtained using lysates from IFNa-treated U87-MG CD4/ CXCR4 cells, where both the long and short isoforms of endogenous IFNa-induced myxovirus resistance 2 (MX2) were shown to interact with CANC complexes, but endogenous MX1 did not (Figure 1B) (Fricke et al, 2014)

Summary

Introduction

Activation of the innate immune response mobilizes an antiviral state. Studies showed that the HIV-1 Capsid (CA) protein is the virus-encoded determinant of MX2 sensitivity, since point mutations in CA can yield MX2-insensitive viruses (Goujon et al, 2013; Kane et al, 2013; Liu et al, 2013; Busnadiego et al, 2014; Matreyek et al, 2014; Bulli et al, 2016) Such mutations may be located on different interfaces of the viral CA, as illustrated by the cyclophilin A (CYPA)-binding loop mutations P90A or G89V, and the hexamer trimeric-interface mutations G208R or T210K, thereby implying a complicated interplay between the CA and MX2. It has been demonstrated that MX2 and the CA can interact in vitro using assemblies of the CA and CA-Nucleocapsid (CANC) as surrogates for the HIV-1 capsid lattice (Fribourgh et al, 2014; Fricke et al, 2014)

Results

Discussion

Conclusion