Human myxovirus resistance protein 1 (MxA) is an interferon-induced dynamin-like GTPase that acts as a cell-autonomous host restriction factor against many viral pathogens including influenza viruses. To study the molecular principles of its antiviral activity, we determined the crystal structure of nucleotide-free MxA, which showed an extended three-domain architecture. The central bundle signaling element (BSE) connected the amino-terminal GTPase domain with the stalk via two hinge regions. MxA oligomerized in the crystal via the stalk and the BSE, which in turn interacted with the stalk of the neighboring monomer. We demonstrated that the intra- and intermolecular domain interplay between the BSE and stalk was essential for oligomerization and the antiviral function of MxA. Based on these results, we propose a structural model for the mechano-chemical coupling in ring-like MxA oligomers as the principle mechanism for this unique antiviral effector protein.

Recently, a novel coronavirus initially designated 2019-nCoV but now termed SARS-CoV-2 has emerged and raised global concerns due to its virulence. SARS-CoV-2 is the etiological agent of "coronavirus disease 2019", abbreviated to COVID-19, which despite only being identified at the very end of 2019, has now been classified as a pandemic by the World Health Organization (WHO). At this time, no specific prophylactic or postexposure therapy for COVID-19 are currently available. Viral entry is the first step in the SARS-CoV-2 lifecycle and is mediated by the trimeric spike protein. Being the first stage in infection, entry of SARS-CoV-2 into host cells is an extremely attractive therapeutic intervention point. Within this review, we highlight therapeutic intervention strategies for anti-SARS-CoV, MERS-CoV, and other coronaviruses and speculate upon future directions for SARS-CoV-2 entry inhibitor designs.

Background: Human myxovirus resistance protein A (MxA) is an antiviral dynamin-related GTPase. Results: Dimerization of MxA via a GTPase domain interface is required for GTP hydrolysis and antiviral activity. Conclusion: GTP binding allows GTPase domain dimerization and membrane-associated assembly of MxA, but it is not sufficient to induce a sustained antiviral effect. Significance: New mechanistic insights into the antiviral action of MxA are provided.

Toscana virus is an emerging bunyavirus in Mediterranean Europe where it accounts for 80% of pediatric meningitis cases during the summer. The negative-strand ribonucleic acid (RNA) genome of the virus is wrapped around the virally encoded nucleoprotein N to form the ribonucleoprotein complex (RNP). We determined crystal structures of hexameric N alone (apo) and in complex with a nonameric single-stranded RNA. RNA is sequestered in a sequence-independent fashion in a deep groove inside the hexamer. At the junction between two adjacent copies of Ns, RNA binding induced an inter-subunit rotation, which opened the RNA-binding tunnel and created a new assembly interface at the outside of the hexamer. Based on these findings, we suggest a structural model for how binding of RNA to N promotes the formation of helical RNPs, which are a characteristic hallmark of many negative-strand RNA viruses.

The HIV-1 CA protein has gained remarkable attention as a promising therapeutic target for the development of new antivirals, due to its pivotal roles in HIV-1 replication (structural and regulatory). Herein, we report the design and synthesis of three series of benzenesulfonamide-containing phenylalanine derivatives obtained by further structural modifications of PF-74 to aid in the discovery of more potent and drug-like HIV-1 CA inhibitors. Structure–activity relationship studies of these compounds led to the identification of new phenylalanine derivatives with a piperazinone moiety, represented by compound 11l, which exhibited anti-HIV-1NL4–3 activity 5.78-fold better than PF-74. Interestingly, 11l also showed anti-HIV-2ROD activity (EC50 = 31 nM), with almost 120 times increased potency over PF-74. However, due to the higher significance of HIV-1 as compared to HIV-2 for the human population, this manuscript focuses on the mechanism of action of our compounds in the context of HIV-1. SPR studies on representative compounds confirmed CA as the binding target. The action stage determination assay demonstrated that these inhibitors exhibited antiviral activities with a dual-stage inhibition profile. The early-stage inhibitory activity of compound 11l was 6.25 times more potent as compared to PF-74 but appeared to work via the accelerating capsid core assembly rather than stabilization. However, the mechanism by which they exert their antiviral activity in the late stage appears to be the same as PF-74 with less infectious HIV-1 virions produced in their presence, as judged p24 content studies. MD simulations provided the key rationale for the promising antiviral potency of 11l. Additionally, 11l exhibited a modest increase in HLM and human plasma metabolic stabilities as compared to PF-74, as well as a moderately improved pharmacokinetic profile, favorable oral bioavailability, and no acute toxicity. These studies provide insights and serve as a starting point for subsequent medicinal chemistry efforts in optimizing these promising HIV inhibitors.

Novel phenylalanine derivatives were discovered as HIV-1 capsid protein inhibitors via “click reaction”. Most of them exhibited remarkable anti-HIV-1 activity.

Only a minority of patients infected with seasonal influenza A viruses exhibits a severe or fatal outcome of infection, but the reasons for this inter-individual variability in influenza susceptibility are unclear. To gain further insights into the molecular mechanisms underlying this variability, we investigated naturally occurring allelic variations of the myxovirus resistance 1 (MX1) gene coding for the influenza restriction factor MxA. The interferon-induced dynamin-like GTPase consists of an N-terminal GTPase domain, a bundle signaling element, and a C-terminal stalk responsible for oligomerization and viral target recognition. We used online databases to search for variations in the MX1 gene. Deploying in vitro approaches, we found that non-synonymous variations in the GTPase domain cause the loss of antiviral and enzymatic activities. Furthermore, we showed that these amino acid substitutions disrupt the interface for GTPase domain dimerization required for the stimulation of GTP hydrolysis. Variations in the stalk were neutral or slightly enhanced or abolished MxA antiviral function.http://www.jbc.org/cgi

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