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The Amino Terminus of Herpes Simplex Virus 1 Glycoprotein K (gK) Is Required for gB Binding to Akt, Release of Intracellular Calcium, and Fusion of the Viral Envelope with Plasma Membranes.

Previously, we have shown that the amino terminus of glycoprotein K (gK) binds to the amino terminus of gB and that deletion of the amino-terminal 38 amino acids of gK prevents herpes simplex virus 1 (HSV-1) infection of mouse trigeminal ganglia after ocular infection and virus entry into neuronal axons. Recently, it has been shown that gB binds to Akt during virus entry and induces Akt phosphorylation and intracellular calcium release. Proximity ligation and two-way immunoprecipitation assays using monoclonal antibodies against gB and Akt-1 phosphorylated at S473 [Akt-1(S473)] confirmed that

A Dual Motif in the Hemagglutinin of H5N1 Goose/Guangdong-Like Highly Pathogenic Avian Influenza Virus Strains Is Conserved from Their Early Evolution and Increases both Membrane Fusion pH and Virulence.

Zoonotic highly pathogenic avian influenza viruses (HPAIV) have raised serious public health concerns of a novel pandemic. These strains eme … ompanied by a decreased HA fusion pH. This increased pH sensitivity of H5 HPAIV enables HA-mediated membrane fusion at a higher endosomal pH. Therefore, this HA adaptation may permit infection of cells with less-acidic endosomes, e.g., within the respiratory tract, resulting in an extended organ tropism. Taken together, HA coadaptation to increased acid sensitivi …

The SI strain of measles virus derived from a patient with subacute sclerosing panencephalitis possesses typical genome alterations and unique amino acid changes that modulate receptor specificity and reduce membrane fusion activity.

Subacute sclerosing panencephalitis (SSPE) is a fatal sequela associated with measles and is caused by persistent infection of the brain with measles virus (MV). The SI strain was isolated in 1976 from a patient with SSPE and shows neurovirulence in animals. Genome nucleotide sequence analyses showed that the SI strain genome possesses typical genome alterations for SSPE-derived strains, namely, accumulated amino acid substitutions in the M protein and cytoplasmic tail truncation of the F protein. Through the establishment of an efficient reverse genetics system, a recombinant SI strain expres

The use of hepatitis C virus NS3/4A and secreted alkaline phosphatase to quantitate cell-cell membrane fusion mediated by severe acute respiratory syndrome coronavirus S protein and the receptor angiotensin-converting enzyme 2.

The membrane fusion process mediated by severe acute respiratory syndrome coronavirus (SARS-CoV) S protein and its cellular receptor angiotensin-converting enzyme 2 (ACE2) had been reconstituted using two Chinese hamster ovary (CHO) cell lines that constitutively express these recombinant proteins separately. This system was applied to develop a quantitative measurement of cell-cell fusion using hepatitis C virus (HCV) NS3/4A protease and a secretion-blocked EGFP-4A/4B-SEAP (EGFP: enhanced green fluorescent protein; 4A/4B: a decapeptide substrate of NS3/4A protease; SEAP: secreted alkaline pho…

Molecular basis of selective mitochondrial fusion by heterotypic action between OPA1 and cardiolipin.

Mitochondria are highly dynamic organelles that undergo frequent fusion and fission. Optic atrophy 1 (OPA1) is an essential GTPase protein f … and cardiolipin (CL) cooperate in heterotypic mitochondrial IM fusion. We reconstituted an in vitro membrane fusion reaction using purified human L-OPA1 protein expressed in silkworm, and found that L-OPA1 on one side of the membrane and CL on the other side are sufficient for fusion. GTP-independent membrane tethering through L-OPA1 and CL primes the subsequent …

A Suitable Membrane Distance Regulated by the RBD_ACE2 Interaction is Critical for SARS-CoV-2 Spike-Mediated Viral Invasion.

The receptor-binding domain (RBD) of spike recognizing the receptor angiotensin-converting enzyme 2 (ACE2) initiates membrane fusion between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and cell membrane. Although the structure of the RBD_ACE2 complex has been well studied, its functional mechanism in membrane fusion is still not fully understood. Here, using an in vitro cell-vesicle content-mixing assay, it is found that the cleavage at the S2' site by thrombin (Thr) protease strongly accelerates membrane fusion, compared to that of cleavage at the S1/S2 site by PreScission (3…

Involvement of lipids in different steps of the flavivirus fusion mechanism.

Flavivirus membrane fusion is triggered by acidic pH and mediated by the major envelope protein E. A structurally very similar fusion protein is found in alphaviruses, and these molecules are designated class II viral fusion proteins. In contrast to that of flaviviruses, however, alphavirus fusion has been shown to be absolutely dependent on the presence of cholesterol and sphingomyelin in the target membrane, suggesting significant differences in the fusion protein-membrane interactions that lead to fusion. With the flavivirus tick-borne encephalitis virus (TBEV), we have therefore conducted …

The Conserved Fusion Peptide Sequence of SARS Coronaviruses Kinetically Promotes the Fusion Pore Opening.

Enveloped viruses enter the cell through the fusion of the viral envelope with the host membrane. These viruses either fuse at the plasma me … ) in a one-intermediate fusion model provides a detailed insight into the mechanistic role of FP in membrane fusion. We have further shown that the peptide binding does not alter the hydrodynamic diameters, ζ and dipole potentials of membranes with varying lipid composition. To understand the plausible role of FP in inducing membrane fusion, we have examined the …

Calcium-Dependent Rubella Virus Fusion Occurs in Early Endosomes.

UNLABELLED: The E1 membrane protein of rubella virus (RuV) is a class II membrane fusion protein structurally related to the fusion proteins of the alphaviruses, flaviviruses, and phleboviruses. Virus entry is mediated by a low pH-dependent fusion reaction through E1's insertion into the cell membrane and refolding to a stable homotrimer. Unlike the other described class II proteins, RuV E1 contains 2 fusion loops, which complex a metal ion between them by interactions with residues N88 and D136. Insertion of the E1 protein into the target membrane, fusion, and infection require calcium and ar…

Inhibition of HIV-1 by fusion inhibitors.

The envelope glycoprotein complex (Env) is responsible for entry of the human immunodeficiency virus type 1 (HIV-1) into cells by mediating attachment to target cells and subsequent membrane fusion. Env consists of three gp120 subunits that mediate receptor and co-receptor attachment and three gp41 subunits responsible for membrane fusion. Several steps of the entry process can serve as drug targets. Receptor antagonists prevent attachment of gp120 to the receptor or co-receptor and conformational changes within gp41 required for membrane fusion can be inhibited by fusion inhibitors. Enfuvirti…

Effect of the S2' site cleavage on SARS-CoV-2 spike.

SARS-CoV-2 initiates infection of host cells by fusing its envelope lipid bilayer with the cell membrane. To overcome kinetic barriers for membrane fusion, the virus-encoded spike (S) protein refolds from a metastable prefusion state to a lower energy, stable postfusion conformation. The protein is first split into S1 and S2 fragments at a proteolytic site after synthesis, and presumably further cleaved at a second site, known as the S2' site, before membrane fusion can occur. Here, we report a cryo-EM structure of S2 fragment after the S2' cleavage, possibly representing a late fusion interme…

Cleavage-Activation of Respiratory Viruses - Half a Century of History from Sendai Virus to SARS-CoV-2.

Many viruses require the cleavage-activation of membrane fusion proteins by host proteases in the course of infection. This knowledge is based on historical studies of Sendai virus in the 1970s. From the 1970s to the 1990s, avian influenza virus and Newcastle disease virus were studied, showing a clear link between virulence and the cleavage-activation of viral membrane fusion proteins (hemagglutinin and fusion proteins) by host proteases. In these viruses, cleavage of viral membrane fusion proteins by furin is the basis for their high virulence. Subsequently, from the 2000s to the 2010s, the …

Membrane topology analysis of HIV-1 envelope glycoprotein gp41.

BACKGROUND: The gp41 subunit of the HIV-1 envelope glycoprotein (Env) has been widely regarded as a type I transmembrane protein with a sing … mpermeable ligand specific to HaloTag was used in the mammalian system. RESULTS: In the absence of membrane fusion, both the prokaryotic and mammalian systems (293FT cells) supported the single MSD model. In the presence of membrane fusion in mammalian cells (293CD4 cells), the data obtained seem to support the multiple MSD model. However, the region predicted t …

On the role of surrounding regions in the fusion peptide in dengue virus infection.

Dengue virus infection depends on its fusion with the host membrane, where the binding occurs through interaction between proteins on the virus cell surface and specific viral receptors on target membranes. This process is mediated by the fusion peptide located between residues 98 and 112 (DRGWGNGCGLFGKGG) that forms a loop in domain II of dengue E glycoprotein. In this study, we evaluated the role of fusion peptide surrounding regions (88-97 and 113-123) of the Dengue 2 subtype on its interaction with the membrane and fusion activity. These sequences are important to stabilize the fusion pept

Phospholipid binding of the dengue virus envelope E protein segment containing the conserved His residue.

Flaviviruses encompass many important human pathogens, including Dengue, Zika, West Nile, Yellow fever, Japanese encephalitis, and Tick-borne encephalitis viruses as well as several emerging viruses that affect millions of people worldwide. They enter cells by endocytosis, fusing their membrane with the late endosomal one in a pH-dependent manner, so membrane fusion is one of the main targets for obtaining new antiviral inhibitors. The envelope E protein, a class II membrane fusion protein, is responsible for fusion and contains different domains involved in the fusion mechanism, including the…

Beyond independent roles: spatiotemporal coupling between viral fusion proteins and viroporins in viral replication and host inflammation.

Membrane fusion and permeabilization are key membrane remodeling processes hijacked by viruses. Although fusion proteins and viroporins have long been characterized as discrete functional modules, emerging evidence supports the spatiotemporal coordination through shared regulation of ion flux, pH homeostasis, membrane tension, organelle stress, and vesicular trafficking during viral infections. These synchronized membrane events synergistically shape viral replication and host immune responses. This review establishes a fusion-ion-inflammation axis to guide mechanistic exploration and antivira…

Эбола Вирус Гликопротеин сильно соединен с мембранесом в отсутствие рецептора.

Вирус Эбола (ЭБОВ) — окрашенный вирус, который должен сплавляться с мембраной ведущих клеток, чтобы высвободить свой геном и начать инфекцию. Этот процесс требует действия конверта EBOV glycoprotein (GP), закодированного вирусом, который проживает в вирусном конверте и состоит из связующего узла рецептора, GP1, и подблока мембранного синтеза, GP2. Несмотря на обширные исследования, механистическое понимание процесса вирусного синтеза является неполным. Для изучения связи GP-membrane, ключевого шага в процессе синтеза, мы использовали два подхода: высокопроизводительные измерения диффузии отдел

Совпадение в аннотации оригинала
Ebola virus (EBOV) is an enveloped virus that must fuse with the host cell membrane in order to release its genome and initiate infection. This process requires the action of the EBOV envelope glycoprotein (GP), encoded by the virus, which resides in the viral envelope and consists of a receptor binding subunit, GP1, and a membrane fusion subunit, GP2. Despi…

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. Here, we investigated how destabilizing or stabilizing mutations in or near the fusion peptide affect v…

Ectodomain Pulling Combines with Fusion Peptide Inserting to Provide Cooperative Fusion for Influenza Virus and HIV.

Enveloped viruses include the most dangerous human and animal pathogens, in particular coronavirus, influenza virus, and human immunodeficiency virus (HIV). For these viruses, receptor binding and entry are accomplished by a single viral envelope protein (termed the fusion protein), the structural changes of which trigger the remodeling and merger of the viral and target cellular membranes. The number of fusion proteins required for fusion activity is still under debate, and several studies report this value to range from 1 to 9 for type I fusion proteins. Here, we consider the earliest stage

Insights into the mechanism of action of the bipartite fusion module of SARS-CoV-2 spike protein.

UNLABELLED: SARS-CoV-2 entry into host cells is mediated by the spike glycoprotein, which promotes fusion between viral and host membranes. Despite its importance, the precise location and mode of action of the fusion peptide, a key spike region that inserts into and perturbs the host membrane, remain elusive. Two regions have been proposed as fusion peptides: one located at the N-terminus of the protein (nFP) and the other at an internal position (iFP). Here, we combine computational and experimental approaches to characterize their roles and impact on membrane fusion. Molecular dynamics (MD)…