Mechanical Properties of Viruses.

Structural biology techniques have greatly contributed to unveiling the interplay between molecular structure, physico-chemical properties, and biological function of viruses. In recent years, classic structural approaches are being complemented by single-molecule techniques such as atomic force microscopy and optical tweezers to study physical features of viral particles that are not accessible to classic structural techniques. Among these features are mechanical properties such as stiffness, intrinsic elasticity, tensile strength, and material fatigue.

Atomic Force Microscopy of Viruses.

Atomic force microscopy (AFM) makes it possible to obtain images at nanometric resolution, and to accomplish the manipulation and physical characterization of specimens, including the determination of their mechanical and electrostatic properties. AFM has an ample range of applications, from materials science to biology. The specimen, supported on a solid surface, can be imaged and manipulated while working in air, ultra-high vacuum or, most importantly for virus studies, in liquid.

Broad Adaptability of Coronavirus Adhesion Revealed from the Complementary Surface Affinity of Membrane and Spikes.

Coronavirus stands for a large family of viruses characterized by protruding spikes surrounding a lipidic membrane adorned with proteins. The present study explores the adhesion of transmissible gastroenteritis coronavirus (TGEV) particles on a variety of reference solid surfaces that emulate typical virus-surface interactions. Atomic force microscopy informs about trapping effectivity and the shape of the virus envelope on each surface, revealing that the deformation of TGEV particles spans from 20% to 50% in diameter.

Gutless Helper-Dependent and First-Generation HAdV5 Vectors Have Similar Mechanical Properties and Common Transduction Mechanisms.

Delivering vectorized information into cells with the help of viruses has been of high interest to fundamental and applied science, and bears significant therapeutic promise. Human adenoviruses (HAdVs) have been at the forefront of gene delivery for many years, and the subject of intensive development resulting in several generations of agents, including replication-competent, -defective or retargeted vectors, and recently also helper-dependent (HD), so-called gutless vectors lacking any viral protein coding information. While it is possible to produce HD-AdVs in significant amounts, physical properties of these virus-like particles and their efficiency of transduction have not been addressed.

Mechanical disassembly of human picobirnavirus like particles indicates that cargo retention is tuned by the RNA-coat protein interaction.

Here we investigate the cargo retention of individual human picobirnavirus (hPBV) virus-like particles (VLPs) which differ in the N-terminal of their capsid protein (CP): (i) hPBV CP contains the full-length CP sequence; (ii) hPBV Δ45-CP lacks the first 45 N-terminal residues; and (iii) hPBV Ht-CP is the full-length CP with a N-terminal 36-residue tag that includes a 6-His segment. Consequently, each VLP variant holds a different interaction with the ssRNA cargo. We used atomic force microscopy (AFM) to induce and monitor the mechanical disassembly of individual hPBV particles.

Mechanical tomography of an archaeal lemon-shaped virus reveals membrane-like fluidity of the capsid and liquid nucleoprotein cargo.

Archaeal lemon-shaped viruses have unique helical capsids composed of highly hydrophobic protein strands which can slide past each other resulting in remarkable morphological reorganization. Here, using atomic force microscopy, we explore the biomechanical properties of the lemon-shaped virions of Sulfolobus monocaudavirus 1 (SMV1), a double-stranded DNA virus which infects hyperthermophilic (~80 °C) and acidophilic (pH ~ 2) archaea. Our results reveal that SMV1 virions are extremely soft and withstand repeated extensive deformations, reaching remarkable strains of 80% during multiple cycles of consecutive mechanical assaults, yet showing scarce traces of disruption.

Atomic Force Microscopy of Viruses: Stability, Disassembly, and Genome Release.

In atomic force microscopy (AFM), the probe is a nanometric tip located at the end of a microcantilever which palpates the specimen under study as a blind person manages a walking stick. In this way, AFM allows obtaining nanometric resolution images of individual protein shells, such as viruses, in liquid milieu. Beyond imaging, AFM also enables not only the manipulation of single protein cages but also the evaluation of each physicochemical property which is able of inducing any measurable mechanical perturbation to the microcantilever that holds the tip.

Single-Molecule Analysis of Genome Uncoating from Individual Human Rhinovirus Particles, and Modulation by Antiviral Drugs.

Infection of humans by many viruses is typically initiated by the internalization of a single virion in each of a few susceptible cells. Thus, the outcome of the infection process may depend on stochastic single-molecule events. A crucial process for viral infection, and thus a target for developing antiviral drugs, is the uncoating of the viral genome.

Exploring nucleic acid condensation and release from individual parvovirus particles with different physicochemical cues.

In the infection cycle, viruses release their genome in the host cell during uncoating. Here we use a variety of physicochemical procedures to induce and monitor the in vitro uncoating of ssDNA from individual Minute Virus of Mice (MVM) particles. Our experiments revealed two pathways of genome release: i) filamentous ssDNA appearing around intact virus particles when using gradual mechanical fatigue and heating at moderate temperature (50 °C).

Surface characterization of alkane viral anchoring films prepared by titanate-assisted organosilanization.

Studies of virus adsorption on surfaces with optimized properties have attracted a lot of interest, mainly due to the influence of the surface in the retention, orientation and stability of the viral capsids. Besides, viruses in whole or in parts can be used as cages or vectors in different areas, such as biomedicine and materials science. A key requirement for virus nanocage application is their physical properties, i.

Electromechanical Photophysics of GFP Packed Inside Viral Protein Cages Probed by Force-Fluorescence Hybrid Single-Molecule Microscopy.

Packing biomolecules inside virus capsids has opened new avenues for the study of molecular function in confined environments. These systems not only mimic the highly crowded conditions in nature, but also allow their manipulation at the nanoscale for technological applications. Here, green fluorescent proteins are packed in virus-like particles derived from P22 bacteriophage procapsids.

Monitoring SARS-CoV-2 Surrogate TGEV Individual Virions Structure Survival under Harsh Physicochemical Environments.

Effective airborne transmission of coronaviruses via liquid microdroplets requires a virion structure that must withstand harsh environmental conditions. Due to the demanding biosafety requirements for the study of human respiratory viruses, it is important to develop surrogate models to facilitate their investigation. Here we explore the mechanical properties and nanostructure of transmissible gastroenteritis virus (TGEV) virions in liquid milieu and their response to different chemical agents commonly used as biocides.

Seeing and touching adenovirus: complementary approaches for understanding assembly and disassembly of a complex virion.

Understanding adenovirus assembly and disassembly poses many challenges due to the virion complexity. A distinctive feature of adenoviruses is the large amount of virus-encoded proteins packed together with the dsDNA genome. Cryo-electron microscopy (cryo-EM) structures are broadening our understanding of capsid variability along evolution, but little is known about the organization of the non-icosahedral nucleoproteic core and its influence in adenovirus function.

Acidification induces condensation of the adenovirus core.

The adenovirus (AdV) icosahedral capsid encloses a nucleoprotein core formed by the dsDNA genome bound to numerous copies of virus-encoded, positively charged proteins. For an efficient delivery of its genome, AdV must undergo a cascade of dismantling events from the plasma membrane to the nuclear pore. Throughout this uncoating process, the virion moves across potentially disruptive environments whose influence in particle stability is poorly understood.

Enhancing Visible-Light Photocatalysis Endohedral Functionalization of Single-Walled Carbon Nanotubes with Organic Dyes.

The encapsulation of an organic dye, 10-phenylphenothiazine (), in the inner cavity of single-walled carbon nanotubes (SWNTs) as a breaking heterogenization strategy is presented. The material was microscopically and spectroscopically characterized, showing intense photoemission when illuminated with visible light at the nanoscale. Thus, was employed as a heterogeneous photocatalyst in single electron transfer dehalogenation reactions under visible light irradiation.

Virucidal Action Mechanism of Alcohol and Divalent Cations Against Human Adenovirus.

Hygiene and disinfection practices play an important role at preventing spread of viral infections in household, industrial and clinical settings. Although formulations based on >70% ethanol are virucidal, there is a currently a need to reformulate products with much lower alcohol concentrations. It has been reported that zinc can increase the virucidal activity of alcohols, although the reasons for such potentiation is unclear.

Fluctuating nonlinear spring theory: Strength, deformability, and toughness of biological nanoparticles from theoretical reconstruction of force-deformation spectra.

We developed the Fluctuating Nonlinear Spring (FNS) model to describe the dynamics of mechanical deformation of biological particles, such as virus capsids. The theory interprets the force-deformation spectra in terms of the "Hertzian stiffness" (non-linear regime of a particle's small-amplitude deformations), elastic constant (large-amplitude elastic deformations), and force range in which the particle's fracture occurs. The FNS theory enables one to quantify the particles' elasticity (Young's moduli for Hertzian and bending deformations), and the limits of their strength (critical forces, fracture toughness) and deformability (critical deformations) as well as the probability distributions of these properties, and to calculate the free energy changes for the particle's Hertzian, elastic, and plastic deformations, and eventual fracture.

Cryo-electron Microscopy Structure, Assembly, and Mechanics Show Morphogenesis and Evolution of Human Picobirnavirus.

Despite their diversity, most double-stranded-RNA (dsRNA) viruses share a specialized T=1 capsid built from dimers of a single protein that provides a platform for genome transcription and replication. This ubiquitous capsid remains structurally undisturbed throughout the viral cycle, isolating the genome to avoid triggering host defense mechanisms. Human picobirnavirus (hPBV) is a dsRNA virus frequently associated with gastroenteritis, although its pathogenicity is yet undefined.

Dynamic competition for hexon binding between core protein VII and lytic protein VI promotes adenovirus maturation and entry.

Adenovirus minor coat protein VI contains a membrane-disrupting peptide that is inactive when VI is bound to hexon trimers. Protein VI must be released during entry to ensure endosome escape. Hexon:VI stoichiometry has been uncertain, and only fragments of VI have been identified in the virion structure.

Multifunctional carbon nanotubes covalently coated with imine-based covalent organic frameworks: exploring structure-property relationships through nanomechanics.

The assembly of 3-dimensional covalent organic frameworks on the surface of carbon nanotubes is designed and successfully developed for the first time via the hybridization of imine-based covalent organic frameworks (COF-300) and oxidized MWCNTs by one-pot chemical synthesis. The resulting hybrid material ox-MWCNTs@COF exhibits a conformal structure that consists of a uniform amorphous COF layer covering the ox-MWCNT surface. The measurements of individual hybrid nanotube mechanical strength performed with atomic force microscopy provide insights into their stability and resistance.

The application of atomic force microscopy for viruses and protein shells: Imaging and spectroscopy.

Atomic force microscopy (AFM) probes surface-adsorbed samples at the nanoscale by using a sharp stylus of nanometric size located at the end of a micro-cantilever. This technique can also work in a liquid environment and offers unique possibilities to study individual protein assemblies, such as viruses, under conditions that resemble their natural liquid milieu. Here, I show how AFM can be used to explore the topography of viruses and protein cages, including that of structures lacking a well-defined symmetry.

Adenovirus major core protein condenses DNA in clusters and bundles, modulating genome release and capsid internal pressure.

Some viruses package dsDNA together with large amounts of positively charged proteins, thought to help condense the genome inside the capsid with no evidence. Further, this role is not clear because these viruses have typically lower packing fractions than viruses encapsidating naked dsDNA. In addition, it has recently been shown that the major adenovirus condensing protein (polypeptide VII) is dispensable for genome encapsidation.

Loading the dice: The orientation of virus-like particles adsorbed on titanate assisted organosilanized surfaces.

The organization of virus-like particles (VLPs) on surfaces is a relevant matter for both fundamental and biomedical sciences. In this work, the authors have tailored surfaces with different surface tension components aiming at finding a relationship with the affinity of the different geometric/surface features of icosahedral P22 VLPs. The surfaces have been prepared by titanate assisted organosilanization with glycidyloxy, amino, and perfluoro silanes.