-
Advances in Anatomy, Embryology, and... 2017Herpes simplex virus mediates multiple distinct fusion events during infection. HSV entry is initiated by fusion of the viral envelope with either the limiting membrane... (Review)
Review
Herpes simplex virus mediates multiple distinct fusion events during infection. HSV entry is initiated by fusion of the viral envelope with either the limiting membrane of a host cell endocytic compartment or the plasma membrane. In the infected cell during viral assembly, immature, enveloped HSV particles in the perinuclear space fuse with the outer nuclear membrane in a process termed de-envelopment. A cell infected with some strains of HSV with defined mutations spread to neighboring cells by a fusion event called syncytium formation. Two experimental methods, the transient cell-cell fusion approach and fusion from without, are useful surrogate assays of HSV fusion. These five fusion processes are considered in terms of their requirements, mechanism, and regulation. The execution and modulation of these events require distinct yet often overlapping sets of viral proteins and host cell factors. The core machinery of HSV gB, gD, and the heterodimer gH/gL is required for most if not all of the HSV fusion mechanisms.
Topics: Animals; Cell Fusion; Herpes Simplex; Humans; Simplexvirus; Viral Proteins; Virus Assembly; Virus Internalization
PubMed: 28528438
DOI: 10.1007/978-3-319-53168-7_2 -
Current Opinion in Virology Aug 2018Virus infections are ultimately dependent on a successful viral genome delivery to the host cell. The bacteriophage family Caudovirales evolved specialized machinery... (Review)
Review
Virus infections are ultimately dependent on a successful viral genome delivery to the host cell. The bacteriophage family Caudovirales evolved specialized machinery that fulfills this function: the portal proteins complex. The complexes are arranged as dodecameric rings and are a structural part of capsids incorporated at a five-fold vertex. They are involved in crucial aspects of viral replication, such as virion assembly, DNA packaging and DNA delivery. This review focuses on the organization and the mechanism through which these portal complexes achieve viral genome delivery and their similarities to other viral portal complexes.
Topics: Bacteriophages; Capsid; Capsid Proteins; DNA Packaging; Genome, Viral; Models, Molecular; Virion; Virus Assembly
PubMed: 30274853
DOI: 10.1016/j.coviro.2018.09.004 -
MBio Oct 2021In 2019, a new pandemic virus belonging to the betacoronavirus family emerged, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This new coronavirus...
In 2019, a new pandemic virus belonging to the betacoronavirus family emerged, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This new coronavirus appeared in Wuhan, China, and is responsible for severe respiratory pneumonia in humans, namely, coronavirus disease 2019 (COVID-19). Having infected almost 200 million people worldwide and caused more than 4.1 million deaths as of today, this new disease has raised a significant number of questions about its molecular mechanism of replication and, in particular, how infectious viral particles are produced. Although viral entry is well characterized, the full assembly steps of SARS-CoV-2 have still not been fully described. Coronaviruses, including SARS-CoV-2, have four main structural proteins, namely, the spike glycoprotein (S), the membrane glycoprotein (M), the envelope protein (E), and the nucleocapsid protein (N). All these proteins have key roles in the process of coronavirus assembly and budding. In this review, we gathered the current knowledge about betacoronavirus structural proteins involved in viral particle assembly, membrane curvature and scission, and then egress in order to suggest and question a coherent model for SARS-CoV-2 particle production and release.
Topics: Betacoronavirus; Membrane Glycoproteins; Nucleocapsid Proteins; SARS-CoV-2; Spike Glycoprotein, Coronavirus; Virus Assembly
PubMed: 34579570
DOI: 10.1128/mBio.02371-21 -
Nature Chemical Biology Mar 2020Although viruses are extremely diverse in shape and size, evolution has led to a limited number of viral classes or lineages, which is probably linked to the assembly... (Review)
Review
Although viruses are extremely diverse in shape and size, evolution has led to a limited number of viral classes or lineages, which is probably linked to the assembly constraints of a viable capsid. Viral assembly mechanisms are restricted to two general pathways, (i) co-assembly of capsid proteins and single-stranded nucleic acids and (ii) a sequential mechanism in which scaffolding-mediated capsid precursor assembly is followed by genome packaging. Cryo-electron microscopy (cryo-EM) and cryo-electron tomography (cryo-ET), which are revolutionizing structural biology, are central to determining the high-resolution structures of many viral assemblies as well as those of assembly intermediates. This wealth of cryo-EM data has also led to the development and redesign of virus-based platforms for biomedical and biotechnological applications. In this Review, we will discuss recent viral assembly analyses by cryo-EM and cryo-ET showing how natural assembly mechanisms are used to encapsulate heterologous cargos including chemicals, enzymes, and/or nucleic acids for a variety of nanotechnological applications.
Topics: Capsid; Capsid Proteins; Cryoelectron Microscopy; Crystallography, X-Ray; Models, Molecular; Nucleic Acid Conformation; Protein Conformation; Virus Assembly
PubMed: 32080621
DOI: 10.1038/s41589-020-0477-1 -
The Enzymes 2021Although the process of genome encapsidation is highly conserved in tailed bacteriophages and eukaryotic double-stranded DNA viruses, there are two distinct packaging... (Review)
Review
Although the process of genome encapsidation is highly conserved in tailed bacteriophages and eukaryotic double-stranded DNA viruses, there are two distinct packaging pathways that these viruses use to catalyze ATP-driven translocation of the viral genome into a preassembled procapsid shell. One pathway is used by ϕ29-like phages and adenoviruses, which replicate and subsequently package a monomeric, unit-length genome covalently attached to a virus/phage-encoded protein at each 5'-end of the dsDNA genome. In a second, more ubiquitous packaging pathway characterized by phage lambda and the herpesviruses, the viral DNA is replicated as multigenome concatemers linked in a head-to-tail fashion. Genome packaging in these viruses thus requires excision of individual genomes from the concatemer that are then translocated into a preassembled procapsid. Hence, the ATPases that power packaging in these viruses also possess nuclease activities that cut the genome from the concatemer at the beginning and end of packaging. This review focuses on proposed mechanisms of genome packaging in the dsDNA viruses using unit-length ϕ29 and concatemeric λ genome packaging motors as representative model systems.
Topics: Bacteriophage lambda; DNA Packaging; DNA, Viral; Viral Genome Packaging; Virus Assembly
PubMed: 34861943
DOI: 10.1016/bs.enz.2021.09.006 -
Viruses Sep 2016Like other retroviruses, human immunodeficiency virus type 1 (HIV-1) selectively packages genomic RNA (gRNA) during virus assembly. However, in the absence of the gRNA,... (Review)
Review
Like other retroviruses, human immunodeficiency virus type 1 (HIV-1) selectively packages genomic RNA (gRNA) during virus assembly. However, in the absence of the gRNA, cellular messenger RNAs (mRNAs) are packaged. While the gRNA is selected because of its cis-acting packaging signal, the mechanism of this selection is not understood. The affinity of Gag (the viral structural protein) for cellular RNAs at physiological ionic strength is not much higher than that for the gRNA. However, binding to the gRNA is more salt-resistant, implying that it has a higher non-electrostatic component. We have previously studied the spacer 1 (SP1) region of Gag and showed that it can undergo a concentration-dependent conformational transition. We proposed that this transition represents the first step in assembly, i.e., the conversion of Gag to an assembly-ready state. To explain selective packaging of gRNA, we suggest here that binding of Gag to gRNA, with its high non-electrostatic component, triggers this conversion more readily than binding to other RNAs; thus we predict that a Gag-gRNA complex will nucleate particle assembly more efficiently than other Gag-RNA complexes. New data shows that among cellular mRNAs, those with long 3'-untranslated regions (UTR) are selectively packaged. It seems plausible that the 3'-UTR, a stretch of RNA not occupied by ribosomes, offers a favorable binding site for Gag.
Topics: Gene Products, gag; Genome, Viral; HIV-1; Humans; RNA, Viral; Virus Assembly
PubMed: 27626441
DOI: 10.3390/v8090246 -
Proceedings of the National Academy of... Nov 2018Flaviviruses assemble initially in an immature, noninfectious state and undergo extensive conformational rearrangements to generate mature virus. Previous cryo-electron...
Flaviviruses assemble initially in an immature, noninfectious state and undergo extensive conformational rearrangements to generate mature virus. Previous cryo-electron microscopy (cryo-EM) structural studies of flaviviruses assumed icosahedral symmetry and showed the concentric organization of the external glycoprotein shell, the lipid membrane, and the internal nucleocapsid core. We show here that when icosahedral symmetry constraints were excluded in calculating the cryo-EM reconstruction of an immature flavivirus, the nucleocapsid core was positioned asymmetrically with respect to the glycoprotein shell. The core was positioned closer to the lipid membrane at the proximal pole, and at the distal pole, the outer glycoprotein spikes and inner membrane leaflet were either perturbed or missing. In contrast, in the asymmetric reconstruction of a mature flavivirus, the core was positioned concentric with the glycoprotein shell. The deviations from icosahedral symmetry demonstrated that the core and glycoproteins have varied interactions, which likely promotes viral assembly and budding.
Topics: Animals; Chlorocebus aethiops; Cryoelectron Microscopy; Glycoproteins; Lipid Bilayers; Molecular Dynamics Simulation; Nucleocapsid; Vero Cells; Viral Envelope Proteins; Virus Assembly; Virus Release; West Nile virus; Zika Virus
PubMed: 30348794
DOI: 10.1073/pnas.1809304115 -
Trends in Microbiology Jan 2024The recent revolution in imaging techniques and results from RNA footprinting in situ reveal how the bacteriophage MS2 genome regulates both particle assembly and genome... (Review)
Review
The recent revolution in imaging techniques and results from RNA footprinting in situ reveal how the bacteriophage MS2 genome regulates both particle assembly and genome release. We have proposed a model in which multiple packaging signal (PS) RNA-coat protein (CP) contacts orchestrate different stages of a viral life cycle. Programmed formation and release of specific PS contacts with CP regulates viral particle assembly and genome uncoating during cell entry. We hypothesize that molecular frustration, a concept introduced to understand protein folding, can be used to better rationalize how PSs function in both particle assembly and genome release. More broadly this concept may explain the directionality of viral life cycles, for example, the roles of host cofactors in HIV infection. We propose that this is a universal principle in virology that explains mechanisms of host-virus interaction and suggests diverse therapeutic interventions.
Topics: Humans; Capsid Proteins; RNA, Viral; HIV Infections; Genome, Viral; Virus Assembly
PubMed: 37507296
DOI: 10.1016/j.tim.2023.07.003 -
Nano Letters Apr 2021Designer virus-inspired proteins drive the manufacturing of more effective, safer gene-delivery systems and simpler models to study viral assembly. However,...
Designer virus-inspired proteins drive the manufacturing of more effective, safer gene-delivery systems and simpler models to study viral assembly. However, self-assembly of engineered viromimetic proteins on specific nucleic acid templates, a distinctive viral property, has proved difficult. Inspired by viral packaging signals, we harness the programmability of CRISPR-Cas12a to direct the nucleation and growth of a self-assembling synthetic polypeptide into virus-like particles (VLP) on specific DNA molecules. Positioning up to ten nuclease-dead Cas12a (dCas12a) proteins along a 48.5 kbp DNA template triggers particle growth and full DNA encapsidation at limiting polypeptide concentrations. Particle growth rate is further increased when dCas12a is dimerized with a polymerization silk-like domain. Such improved self-assembly efficiency allows for discrimination between cognate versus noncognate DNA templates by the synthetic polypeptide. CRISPR-guided VLPs will help to develop programmable bioinspired nanomaterials with applications in biotechnology as well as viromimetic scaffolds to improve our understanding of viral self-assembly.
Topics: Clustered Regularly Interspaced Short Palindromic Repeats; DNA; Nucleocapsid; Virion; Virus Assembly
PubMed: 33729813
DOI: 10.1021/acs.nanolett.0c04640 -
STAR Protocols Mar 2022This protocol describes the reconstitution of the filamentous Ebola virus nucleocapsid-like assembly . This is followed by solving the cryo-EM structure using helical...
This protocol describes the reconstitution of the filamentous Ebola virus nucleocapsid-like assembly . This is followed by solving the cryo-EM structure using helical reconstruction, and flexible fitting of the existing model into the 5.8 Å cryo-EM map. The protocol can be applied to other filamentous viral protein assemblies, particularly those with high flexibility and moderate resolution maps, which present technical challenges to model building. For complete details on the use and execution of this profile, please refer to Su et al. (2018).
Topics: Cryoelectron Microscopy; Ebolavirus; Hemorrhagic Fever, Ebola; Humans; Nucleocapsid; Virus Assembly
PubMed: 34977676
DOI: 10.1016/j.xpro.2021.101030