Transfer of the Amino-Terminal Nuclear Envelope Targeting Domain of Human MX2 Converts MX1 into an HIV-1 Resistance Factor

et al. 2015

The alpha interferon (IFN-␣)-inducible restriction factor myxovirus B (MxB) blocks HIV-1 infection after reverse transcription but prior to integration. MxB binds to the HIV-1 core, which is composed of capsid protein, and this interaction leads to inhibition of the uncoating process of HIV-1. Previous studies suggested that HIV-1 restriction by MxB requires binding to capsid. This work tests the hypothesis that MxB oligomerization is important for the ability of MxB to bind to the HIV-1 core. For this purpose, we modeled the structure of MxB using the published tertiary structure of MxA. The modeled structure of MxB guided our mutagenic studies and led to the discovery of several MxB variants that lose the capacity to oligomerize. In agreement with our hypothesis, MxB variants that lost the oligomerization capacity also lost the ability to bind to the HIV-1 core. MxB variants deficient for oligomerization were not able to block HIV-1 infection. Overall, our work showed that oligomerization is required for the ability of MxB to bind to the HIV-1 core and block HIV-1 infection. IMPORTANCEMxB is a novel restriction factor that blocks infection of HIV-1. MxB is inducible by IFN-␣, particularly in T cells. The current work studies the oligomerization determinants of MxB and carefully explores the contribution of oligomerization to capsid binding and restriction. This work takes advantage of the current structure of MxA and models the structure of MxB, which is used to guide structure-function studies. This work leads to the conclusion that MxB oligomerization is important for HIV-1 capsid binding and restriction.

supporting

confidence: 89%

Contribution of MxB Oligomerization to HIV-1 Capsid Binding and Restriction

Buffone

et al. 2015

“…We also showed that the ability of MxB to block infection requires a capsid binding domain and an oligomerization domain provided by the 90 N-terminal and 143 C-terminal amino acids of MxB, respectively (24). In addition, the work of others and our work showed that the 90 N-terminal amino acids of MxB are important for its ability to bind capsid and restrict HIV-1 infection (24)(25)(26). MxB contains a previously described putative nuclear localization signal on its N-terminal 25 amino acids (4).…”

supporting

confidence: 56%

“…Residues 20 KY 21 control the ability of the N-terminal domain of MxB to function as a nuclear localization signal. Recent indirect immunofluorescence studies have shown that MxB exhibits a punctate pattern that extends from the cytosol to the perinuclear region of the cell (24)(25)(26)(27)33). To test whether human MxB shuttles between the cytosol and the nucleus, we treated human cells expressing MxB with the drug leptomycin B, which blocks nuclear export by interfering with the CRM1-mediated mechanism (34)(35)(36)(37).…”

Section: Resultsmentioning

confidence: 99%

Restriction of HIV-1 Requires the N-Terminal Region of MxB as a Capsid-Binding Motif but Not as a Nuclear Localization Signal

Buffone

et al. 2015

Section: Introductionmentioning

confidence: 56%

“…We also showed that the ability of MxB to block infection requires a capsid binding domain and an oligomerization domain provided by the 90 N-terminal and the 143 C-terminal amino acids of MxB, respectively (24). In addition, the work of others and our work showed that the 90 N-terminal amino acids of MxB are important for its ability to bind capsid and restrict HIV-1 infection (24)(25)(26).MxB contains a previously described putative nuclear localization signal on its N-terminal 25 amino acids (4). Deletion of the N-terminal 25 amino acids annihilates the ability of MxB to block HIV-1 infection and to bind to the HIV-1 core (23,24,27).…”

mentioning

confidence: 77%

MxB Is Not Responsible for the Blocking of HIV-1 Infection Observed in Alpha Interferon-Treated Cells

Vieira

et al. 2016

MxB restricts HIV-1 infection by directly interacting with the HIV-1 core, which is made of viral capsid; however, the contribution of MxB to the HIV-1 restriction observed in alpha interferon (IFN-␣)-treated human cells is unknown. To understand this contribution, we used HIV-1 bearing the G208R capsid mutant (HIV-1-G208R), which overcomes the restriction imposed by cells expressing MxB. Here we showed that the reason why MxB does not block HIV-1-G208R is that MxB does not interact with HIV-1 cores bearing the mutation G208R. M yxovirus resistance proteins represent a family of interferon-inducible factors with a wide range of antiviral activities (1-3). The myxovirus B (MxB) gene was originally cloned from a human glioblastoma cell line treated with alpha interferon (IFN-␣) (4, 5). MxB as well as the related protein MxA belong to the dynamin-like family of proteins, which have diverse functions ranging from vesicle transport to antiviral activity (1, 6-11). The most studied dynamin-like protein that exhibits antiviral activity is MxA (1, 2). Contrary to MxB, the antiviral role of MxA has been extensively studied for viruses including influenza virus (1, 12-15), tick-borne Thogoto virus (16), African swine fever virus (17), hepatitis B virus (18), and La Crosse virus (19,20). The antiviral activity of the long form of MxB was recently described (9, 21-23); these investigations led to the discovery that the IFN-␣-inducible protein MxB blocks HIV-1 infection.Genetic evidence suggested that the HIV-1 capsid is the determinant for the ability of MxB to block HIV-1 infection (9,22,23). In agreement with these findings, we recently demonstrated that MxB binds to the HIV-1 capsid and correlated the ability of MxB to block HIV-1 infection with inhibition of uncoating (24). We also showed that the ability of MxB to block infection requires a capsid binding domain and an oligomerization domain provided by the 90 N-terminal and the 143 C-terminal amino acids of MxB, respectively (24). In addition, the work of others and our work showed that the 90 N-terminal amino acids of MxB are important for its ability to bind capsid and restrict HIV-1 infection (24)(25)(26).MxB contains a previously described putative nuclear localization signal on its N-terminal 25 amino acids (4). Deletion of the N-terminal 25 amino acids annihilates the ability of MxB to block HIV-1 infection and to bind to the HIV-1 core (23,24,27). Mutagenic studies have revealed that the N-terminal 25 amino acids of MxB exhibit a triple-arginine motif ( 11 RRR 13 ) that is important for restriction and the ability of MxB to bind to the HIV-1 core (28, 29). HIV-1 CA-NC expression and purification. The CA-NC proteins of HIV-1 and HIV-1 bearing the G208R capsid mutant (HIV-1-G208R) were expressed, purified, and assembled as previously described (30). MATERIALS AND METHODS CellMxB binding to in vitro-assembled HIV-1 and HIV-1-G208R CA-NC complexes. HEK 293T cells were transfected with a plasmid expressing the wild-type MxB protein. Forty-eight hours after t...