Influenza A Virus Infections Sense Host Membrane Tension to Dynamically Tune Assembly.

Enveloped viruses often exhibit a pleomorphic morphology, ranging in size from 100nm spheres to tens-of-micron long filaments. For influenza A virus (IAV), spheres enable rapid replication and minimize metabolic cost, while filaments resist effects of antibodies or other cell-entry pressures. The current paradigm is that virion shape changes require genetic adaptation; however, a virus evolved to alter its shape phenotypically would outperform one that relies on genetic selection.

Therapeutic vs. Suprapharmacological Metformin Concentrations: Different Effects on Energy Metabolism and Mitochondrial Function in Skeletal Muscle Cells .

Metformin is an oral antidiabetic agent that has been widely used in clinical practice for over 60 years, and is currently the most prescribed antidiabetic drug worldwide. However, the molecular mechanisms of metformin action in different tissues are still not completely understood. Although metformin-induced inhibition of mitochondrial respiratory chain Complex I and activation of AMP-activated protein kinase have been observed in many studies, published data is inconsistent.

Hemagglutinin Stability Determines Influenza A Virus Susceptibility to a Broad-Spectrum Fusion Inhibitor Arbidol.

Understanding mechanisms of resistance to antiviral inhibitors can reveal nuanced features of targeted viral mechanisms and, in turn, lead to improved strategies for inhibitor design. Arbidol is a broad-spectrum antiviral that binds to and prevents the fusion-associated conformational changes in the trimeric influenza A virus (IAV) hemagglutinin (HA). The rate-limiting step during the HA-mediated membrane fusion is the release of the hydrophobic fusion peptides from a conserved pocket on HA.

The shape of pleomorphic virions determines resistance to cell-entry pressure.

Many enveloped animal viruses produce a variety of particle shapes, ranging from small spherical to long filamentous types. Characterization of how the shape of the virion affects infectivity has been difficult because the shape is only partially genetically encoded, and most pleomorphic virus structures have no selective advantage in vitro. Here, we apply virus fractionation using low-force sedimentation, as well as antibody neutralization coupled with RNAScope, single-particle membrane fusion experiments and stochastic simulations to evaluate the effects of differently shaped influenza A viruses and influenza viruses pseudotyped with Ebola glycoprotein on the infection of cells.

Distinct functional determinants of influenza hemagglutinin-mediated membrane fusion.

Membrane fusion is the critical step for infectious cell penetration by enveloped viruses. We have previously used single-virion measurements of fusion kinetics to study the molecular mechanism of influenza-virus envelope fusion. Published data on fusion inhibition by antibodies to the 'stem' of influenza virus hemagglutinin (HA) now allow us to incorporate into simulations the provision that some HAs are inactive.

Silibinin inhibits hepatitis C virus entry into hepatocytes by hindering clathrin-dependent trafficking.

Hepatitis C virus (HCV) is a global health concern infecting 170 million people worldwide. Previous studies indicate that the extract from milk thistle known as silymarin and its main component silibinin inhibit HCV infection. Here we investigated the mechanism of anti-HCV action of silymarin-derived compounds at the molecular level.

Influenza-virus membrane fusion by cooperative fold-back of stochastically induced hemagglutinin intermediates.

Influenza virus penetrates cells by fusion of viral and endosomal membranes catalyzed by the viral hemagglutinin (HA). Structures of the initial and final states of the HA trimer define the fusion endpoints, but do not specify intermediates. We have characterized these transitions by analyzing low-pH-induced fusion kinetics of individual virions and validated the analysis by computer simulation.

Kinetics of proton transport into influenza virions by the viral M2 channel.

M2 protein of influenza A viruses is a tetrameric transmembrane proton channel, which has essential functions both early and late in the virus infectious cycle. Previous studies of proton transport by M2 have been limited to measurements outside the context of the virus particle. We have developed an in vitro fluorescence-based assay to monitor internal acidification of individual virions triggered to undergo membrane fusion.

Recruitment of cellular clathrin to viral factories and disruption of clathrin-dependent trafficking.

The viral factories of mammalian reovirus (MRV) are cytoplasmic structures that serve as sites of viral genome replication and particle assembly. A 721-aa MRV non-structural protein, µNS, forms the factory matrix and recruits other viral proteins to these structures. In this report, we show that µNS contains a conserved C-proximal sequence (711-LIDFS-715) that is similar to known clathrin-box motifs and is required for recruitment of clathrin to viral factories.

Requirements for the formation of membrane pores by the reovirus myristoylated micro1N peptide.

The outer capsid of the nonenveloped mammalian reovirus contains 200 trimers of the micro1 protein, each complexed with three copies of the protector protein sigma3. Conformational changes in micro1 following the proteolytic removal of sigma3 lead to release of the myristoylated N-terminal cleavage fragment micro1N and ultimately to membrane penetration. The micro1N fragment forms pores in red blood cell (RBC) membranes.

A positive-feedback mechanism promotes reovirus particle conversion to the intermediate associated with membrane penetration.

Membrane penetration by reovirus is associated with conversion of a metastable intermediate, the ISVP, to a further-disassembled particle, the ISVP*. Factors that promote this conversion in cells are poorly understood. Here, we report the in vitro characterization of a positive-feedback mechanism for promoting ISVP* conversion.

Peptides released from reovirus outer capsid form membrane pores that recruit virus particles.

Nonenveloped animal viruses must disrupt or perforate a cell membrane during entry. Recent work with reovirus has shown formation of size-selective pores in RBC membranes in concert with structural changes in capsid protein mu1. Here, we demonstrate that mu1 fragments released from reovirus particles are sufficient for pore formation.

A role for molecular chaperone Hsc70 in reovirus outer capsid disassembly.

After crossing the cellular membrane barrier during cell entry, most animal viruses must undergo further disassembly before initiating viral gene expression. In many cases, these disassembly mechanisms remain poorly defined. For this report, we examined a final step in disassembly of the mammalian reovirus outer capsid: cytoplasmic release of the central, delta fragment of membrane penetration protein mu1 to yield the transcriptionally active viral core particle.

Mammalian reovirus, a nonfusogenic nonenveloped virus, forms size-selective pores in a model membrane.

During cell entry, reovirus particles with a diameter of 70-80 nm must penetrate the cellular membrane to access the cytoplasm. The mechanism of penetration, without benefit of membrane fusion, is not well characterized for any such nonenveloped animal virus. Lysis of RBCs is an in vitro assay for the membrane perforation activity of reovirus; however, the mechanism of lysis has been unknown.

Mode of action for linear peptide inhibitors of HIV-1 gp120 interactions.

The linear peptide 12p1 (RINNIPWSEAMM) was previously isolated from a phage display library and was found to inhibit interaction of HIV-1 gp120 with both CD4 and a CCR5 surrogate, mAb 17b [Ferrer, M., and Harrison, S. (1999) J.

A truncated form of Nef selected during pathogenic reversion of simian immunodeficiency virus SIVmac239Deltanef increases viral replication.

The live, attenuated vaccine simian immunodeficiency virus SIVmac239Deltanef efficiently protects rhesus macaques against infection with wild-type SIVmac but occasionally causes CD4(+) T-cell depletion and progression to simian AIDS (SAIDS). Virus recovered from a vaccinated macaque (Rh1490) that progressed to SAIDS had acquired an additional deletion in the nef gene, resulting in a frameshift that restored the original nef open reading frame (R. I.

Properties of the surface envelope glycoprotein associated with virulence of simian-human immunodeficiency virus SHIV(SF33A) molecular clones.

In vivo adaptation of simian-human immunodeficiency virus (SHIV) clone SHIV(SF33) resulted in the emergence of pathogenic isolate SHIV(SF33A), which caused a rapid and severe CD4(+) T-cell depletion when inoculated into rhesus macaques. Two molecular clones generated by inserting the env V1-to-V5 region amplified from SHIV(SF33A)-infected animals into the parental SHIV(SF33) genome retained a pathogenic phenotype. The gp120 envelope glycoproteins of pathogenic clones SHIV(SF33A2) and SHIV(SF33A5) conferred a threefold increase in viral entry and fusogenicity compared to the parental glycoprotein.