Engineered Tobacco mosaic virus mutants with distinct physical characteristics in planta and enhanced metallization properties

Advancements in Functional Nanomaterials Inspired by Viral Particles

Virus-like particles (VLPs) are nanostructures composed of one or more structural proteins, exhibiting stable and symmetrical structures. Their precise compositions and dimensions provide versatile opportunities for modifications, enhancing their functionality. Consequently, VLP-based nanomaterials have gained widespread adoption across diverse domains. This review focuses on three key aspects: the mechanisms of viral capsid protein self-assembly into VLPs, design methods for constructing multifunctional VLPs, and strategies for synthesizing multidimensional nanomaterials using VLPs. It provides a comprehensive overview of the advancements in virus-inspired functional nanomaterials, encompassing VLP assembly, functionalization, and the synthesis of multidimensional nanomaterials. Additionally, this review explores future directions, opportunities, and challenges in the field of VLP-based nanomaterials, aiming to shed light on potential advancements and prospects in this exciting area of research.

Getting Hold of the Tobamovirus Particle-Why and How? Purification Routes over Time and a New Customizable Approach

This article develops a multi-perspective view on motivations and methods for tobamovirus purification through the ages and presents a novel, efficient, easy-to-use approach that can be well-adapted to different species of native and functionalized virions. We survey the various driving forces prompting researchers to enrich tobamoviruses, from the search for the causative agents of mosaic diseases in plants to their increasing recognition as versatile nanocarriers in biomedical and engineering applications. The best practices and rarely applied options for the serial processing steps required for successful isolation of tobamoviruses are then reviewed. Adaptations for distinct particle species, pitfalls, and 'forgotten' or underrepresented technologies are considered as well. The article is topped off with our own development of a method for virion preparation, rooted in historical protocols. It combines selective re-solubilization of polyethylene glycol (PEG) virion raw precipitates with density step gradient centrifugation in biocompatible iodixanol formulations, yielding ready-to-use particle suspensions. This newly established protocol and some considerations for perhaps worthwhile further developments could serve as putative stepping stones towards preparation procedures appropriate for routine practical uses of these multivalent soft-matter nanorods.

Overcoming biological barriers by virus-like drug particles for drug delivery

Virus-like particles (VLPs) have natural structural antigens similar to those found in viruses, making them valuable in vaccine immunization. Furthermore, VLPs have demonstrated significant potential in drug delivery, and emerged as promising vectors for transporting chemical drug, genetic drug, peptide/protein, and even nanoparticle drug. With virus-like permeability and strong retention, they can effectively target specific organs, tissues or cells, facilitating efficient intracellular drug release. Further modifications allow VLPs to transfer across various physiological barriers, thus acting the purpose of efficient drug delivery and accurate therapy. This article provides an overview of VLPs, covering their structural classifications, deliverable drugs, potential physiological barriers in drug delivery, strategies for overcoming these barriers, and future prospects.

Multifunctional plant virus nanoparticles: An emerging strategy for therapy of cancer

Cancer therapy requires sophisticated treatment strategies to obtain the highest success. Nanotechnology is enabling, revolutionizing, and multidisciplinary concepts to improve conventional cancer treatment modalities. Nanomaterials have a central role in this scenario, explaining why various nanomaterials are currently being developed for cancer therapy. Viral nanoparticles (VNPs) have shown promising performance in cancer therapy due to their unique features. VNPs possess morphological homogeneity, ease of functionalization, biocompatibility, biodegradability, water solubility, and high absorption efficiency that are beneficial for cancer therapy applications. In the current review paper, we highlight state-of-the-art properties and potentials of plant viruses, strategies for multifunctional plant VNPs formulations, potential applications and challenges in VNPs-based cancer therapy, and finally practical solutions to bring potential cancer therapy one step closer to real applications. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Facile Purification and Use of Tobamoviral Nanocarriers for Antibody-Mediated Display of a Two-Enzyme System

Immunosorbent turnip vein clearing virus (TVCV) particles displaying the IgG-binding domains D and E of Staphylococcus aureus protein A (PA) on every coat protein (CP) subunit (TVCVPA) were purified from plants via optimized and new protocols. The latter used polyethylene glycol (PEG) raw precipitates, from which virions were selectively re-solubilized in reverse PEG concentration gradients. This procedure improved the integrity of both TVCVPA and the wild-type subgroup 3 tobamovirus. TVCVPA could be loaded with more than 500 IgGs per virion, which mediated the immunocapture of fluorescent dyes, GFP, and active enzymes. Bi-enzyme ensembles of cooperating glucose oxidase and horseradish peroxidase were tethered together on the TVCVPA carriers via a single antibody type, with one enzyme conjugated chemically to its Fc region, and the other one bound as a target, yielding synthetic multi-enzyme complexes. In microtiter plates, the TVCVPA-displayed sugar-sensing system possessed a considerably increased reusability upon repeated testing, compared to the IgG-bound enzyme pair in the absence of the virus. A high coverage of the viral adapters was also achieved on Ta2O5 sensor chip surfaces coated with a polyelectrolyte interlayer, as a prerequisite for durable TVCVPA-assisted electrochemical biosensing via modularly IgG-assembled sensor enzymes.

Characterizing Heterogeneous Mixtures of Assembled States of the Tobacco Mosaic Virus Using Charge Detection Mass Spectrometry

The tobacco mosaic viral capsid protein (TMV) is a frequent target for derivatization for myriad applications, including drug delivery, biosensing, and light harvesting. However, solutions of the stacked disk assembly state of TMV are difficult to characterize quantitatively due to their large size and multiple assembled states. Charge detection mass spectrometry (CDMS) addresses the need to characterize heterogeneous populations of large protein complexes in solution quickly and accurately. Using CDMS, previously unobserved assembly states of TMV, including 16-monomer disks and odd-numbered disk stacks, have been characterized. We additionally employed a peptide-protein conjugation reaction in conjunction with CDMS to demonstrate that modified TMV proteins do not redistribute between disks. Finally, this technique was used to discriminate between protein complexes of near-identical mass but different configurations. We have gained a greater understanding of the behavior of TMV, a protein used across a broad variety of fields and applications, in the solution state.

Designer-length palladium nanowires can be templated by the central channel of tobacco mosaic virus nanorods

We have developed methods for the templated synthesis of palladium nanowires (Pd NWs) within the central channel of tobacco mosaic virus (TMV) nanorods of various lengths. We show that uniform 4 nm diameter Pd NWs can be produced by selective growth within these channels by including the capping reagent, poly(vinyl-pyrrolidone) (PVP30K) and reducing the metal precursor to metallic palladium with ascorbic acid. The length of the Pd NWs can be controlled either by varying the length of the nanorod templates and/or through alterations to the reaction conditions. We have also demonstrated bimetallic gold (Au)-palladium (Pd) in-situ metallization of TMV nanorods resulting in the production of Pd NWs 6 nm gold nanoparticles attached to their ends. The materials produced have many potential applications in the construction of nanoscale devices.

Engineering Tobacco Mosaic Virus and Its Virus-Like-Particles for Synthesis of Biotemplated Nanomaterials

Biomolecules are increasingly attractive templates for the synthesis of functional nanomaterials. Chief among them is the plant tobacco mosaic virus (TMV) due to its high aspect ratio, narrow size distribution, diverse biochemical functionalities presented on the surface, and compatibility with a number of chemical conjugations. These properties are also easily manipulated by genetic modification to enable the synthesis of a range of metallic and non-metallic nanomaterials for diverse applications. This article reviews the characteristics of TMV and related viruses, and their virus-like particle (VLP) derivatives, and how these may be manipulated to extend their use and function. A focus of recent efforts has been on greater understanding and control of the self-assembly processes that drive biotemplate formation. How these features have been exploited in engineering applications such as, sensing, catalysis, and energy storage are briefly outlined. While control of VLP surface features is well-established, fewer tools exist to control VLP self-assembly, which limits efforts to control template uniformity and synthesis of certain templated nanomaterials. However, emerging advances in synthetic biology, machine learning, and other fields promise to accelerate efforts to control template uniformity and nanomaterial synthesis enabling more widescale industrial use of VLP-based biotemplates.

High-resolution analyses of the mineralisation process at bio/inorganic interfaces

To gain insight into bio-inspired mineralisation processes that may be directed or influenced by the protein coat of tobacco mosaic virus (TMV), microscopic studies are crucial. The authors elucidate key steps towards the understanding of the mineralisation mechanism by high-resolution transmission electron microscopy imaging of the organic/inorganic interfaces. Wild-type TMV and mutants with distinct surface properties are used to investigate the processes of nucleation and mineral formation based on ZnO and ZnS deposition. The development of suitable sample preparation methods is central in the study, as well as finding the optimal imaging conditions in combination with the use of a latest-generation high-end microscope. The mineralisation is to be analysed with respect to the underlying nucleation process: Correlation of structure findings with mechanical properties will pave the way to the goal of the design of materials with enhanced mechanical properties.

From stars to stripes: RNA-directed shaping of plant viral protein templates-structural synthetic virology for smart biohybrid nanostructures

The self-assembly of viral building blocks bears exciting prospects for fabricating new types of bionanoparticles with multivalent protein shells. These enable a spatially controlled immobilization of functionalities at highest surface densities-an increasing demand worldwide for applications from vaccination to tissue engineering, biocatalysis, and sensing. Certain plant viruses hold particular promise because they are sustainably available, biodegradable, nonpathogenic for mammals, and amenable to in vitro self-organization of virus-like particles. This offers great opportunities for their redesign into novel "green" carrier systems by spatial and structural synthetic biology approaches, as worked out here for the robust nanotubular tobacco mosaic virus (TMV) as prime example. Natural TMV of 300 x 18 nm is built from more than 2,100 identical coat proteins (CPs) helically arranged around a 6,395 nucleotides ssRNA. In vitro, TMV-like particles (TLPs) may self-assemble also from modified CPs and RNAs if the latter contain an Origin of Assembly structure, which initiates a bidirectional encapsidation. By way of tailored RNA, the process can be reprogrammed to yield uncommon shapes such as branched nanoobjects. The nonsymmetric mechanism also proceeds on 3'-terminally immobilized RNA and can integrate distinct CP types in blends or serially. Other emerging plant virus-deduced systems include the usually isometric cowpea chlorotic mottle virus (CCMV) with further strikingly altered structures up to "cherrybombs" with protruding nucleic acids. Cartoon strips and pictorial descriptions of major RNA-based strategies induct the reader into a rare field of nanoconstruction that can give rise to utile soft-matter architectures for complex tasks. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures.

Different forms of African cassava mosaic virus capsid protein within plants and virions

One geminiviral gene encodes the capsid protein (CP), which can appear as several bands after electrophoresis depending on virus and plant. African cassava mosaic virus-Nigeria CP in Nicotiana benthamiana, however, yielded one band (~ 30 kDa) in total protein extracts and purified virions, although its expression in yeast yielded two bands (~ 30, 32 kDa). Mass spectrometry of the complete protein and its tryptic fragments from virions is consistent with a cleaved start M1, acetylated S2, and partial phosphorylation at T12, S25 and S62. Mutants for additional potentially modified sites (N223A; C235A) were fully infectious and formed geminiparticles. Separation in triton acetic acid urea gels confirmed charge changes of the CP between plants and yeast indicating differential phosphorylation. If the CP gene alone was expressed in plants, multiple bands were observed like in yeast. A high turnover rate indicates that post-translational modifications promote CP decay probably via the ubiquitin-triggered proteasomal pathway.

TMV Particles: The Journey From Fundamental Studies to Bionanotechnology Applications

Ever since its initial characterization in the 19th century, tobacco mosaic virus (TMV) has played a prominent role in the development of modern virology and molecular biology. In particular, research on the three-dimensional structure of the virus particles and the mechanism by which these assemble from their constituent protein and RNA components has made TMV a paradigm for our current view of the morphogenesis of self-assembling structures, including viral particles. More recently, this knowledge has been applied to the development of novel reagents and structures for applications in biomedicine and bionanotechnology. In this article, we review how fundamental science has led to TMV being at the vanguard of these new technologies.

M13 bacteriophage spheroids as scaffolds for directed synthesis of spiky gold nanostructures

The spherical form (s-form) of a genetically-modified gold-binding M13 bacteriophage was investigated as a scaffold for gold synthesis. Repeated mixing of the phage with chloroform caused a 15-fold contraction from a nearly one micron long filament to an approximately 60 nm diameter spheroid. The geometry of the viral template and the helicity of its major coat protein were monitored throughout the transformation process using electron microscopy and circular dichroism spectroscopy, respectively. The transformed virus, which retained both its gold-binding and mineralization properties, was used to assemble gold colloid clusters and synthesize gold nanostructures. Spheroid-templated gold synthesis products differed in morphology from filament-templated ones. Spike-like structures protruded from the spherical template while isotropic particles developed on the filamentous template. Using inductively coupled plasma-mass spectroscopy (ICP-MS), gold ion adsorption was found to be comparatively high for the gold-binding M13 spheroid, and likely contributed to the dissimilar gold morphology. Template contraction was believed to modify the density, as well as the avidity of gold-binding peptides on the scaffold surface. The use of the s-form of the M13 bacteriophage significantly expands the templating capabilities of this viral platform and introduces the potential for further morphological control of a variety of inorganic material systems.

Simple Electroless Synthesis of Cobalt Nanoparticle Chains, Oriented by Externally Applied Magnetic Fields

The electroless (chemical) deposition of cobalt on palladium-sensitized oxidized silicon wafers produces nanowires and chains made up by nanoparticles. We demonstrate that the application of moderate magnetic fields, provided by permanent magnets, during the growth produces highly oriented cobalt nanowires and nanoparticle chains. By adjusting the magnetic field direction in plane, parallel and crossed cobalt chain patterns are readily accessible. Perpendicular orientation of the field results in rod-like, standing-up chains of nanoparticles. We explain the observed structures with magnetostatic arguments.

Sensing of heavy metal ions by intrinsic TMV coat protein fluorescence

We propose the use of a cysteine mutant of TMV coat protein as a signal transducer for the selective sensing and quantification of the heavy metal ions, Cd²⁺, Pb²⁺, Zn²⁺ and Ni²⁺ based on intrinsic tryptophan quenching. TMV coat protein is inexpensive, can be mass-produced since it is expressed and extracted from E-coli. It also displays several different functional groups, enabling a wide repertoire of bioconjugation chemistries; thus it can be easily integrated into functional devices. In addition, TMV-ion interactions have been widely reported and utilized for metallization to generate organic-inorganic hybrid composite novel materials. Building on these previous observations, we herein determine, for the first time, the TMV-ion binding constants assuming the static fluorescence quenching model. We also show that by comparing TMV-ion interactions between native and denatured coat protein, we can distinguish between chemically similar heavy metal ions such as cadmium and zinc ions.

Electrochemically-Driven Insertion of Biological Nanodiscs into Solid State Membrane Pores as a Basis for "Pore-In-Pore" Membranes

Nanoporous membranes are of increasing interest for many applications, such as molecular filters, biosensors, nanofluidic logic and energy conversion devices. To meet high-quality standards, e.g., in molecular separation processes, membranes with well-defined pores in terms of pore diameter and chemical properties are required. However, the preparation of membranes with narrow pore diameter distributions is still challenging. In the work presented here, we demonstrate a strategy, a "pore-in-pore" approach, where the conical pores of a solid state membrane produced by a multi-step top-down lithography procedure are used as a template to insert precisely-formed biomolecular nanodiscs with exactly defined inner and outer diameters. These nanodiscs, which are the building blocks of tobacco mosaic virus-deduced particles, consist of coat proteins, which self-assemble under defined experimental conditions with a stabilizing short RNA. We demonstrate that the insertion of the nanodiscs can be driven either by diffusion due to a concentration gradient or by applying an electric field along the cross-section of the solid state membrane. It is found that the electrophoresis-driven insertion is significantly more effective than the insertion via the concentration gradient.

Building expanded structures from tetrahedral DNA branching elements, RNA and TMV protein

By combining both chemical and enzymatic ligation with procedures guiding the self-assembly of nanotubular tobacco mosaic virus (TMV)-like particles (TLPs), novel nucleoprotein structures based on DNA-terminated branching elements, RNA scaffolds and TMV coat protein (CP) are made accessible. Tetrahedral tetrakis(hydroxybiphenyl)adamantane cores with four 5'-phosphorylated dinucleotide arms were coupled to DNA linkers by chemical ligation. The resulting three-dimensional (3D) branching elements were enzymatically ligated to the 3' termini of RNA scaffolds either prior to or after the RNAs' incorporation into TLPs. Thus, architectures with interconnected nanotube domains in two different length classes were generated, each containing 70 CP subunits per 10 nm length. Short TMV origin-of-assembly-containing RNA scaffolds ligated to the DNA allowed the growth of protein-coated 34 nm tubes on the terminal RNA strands in situ. Alternatively, 290 nm pre-fabricated tubes with accessible RNA 3' termini, attained by DNA blocking elements hybridized to the RNAs, were ligated with the branched cores. Both approaches resulted in four-armed nanoobjects, demonstrating a so far unique combination of organic synthesis of branching elements, enzymatic modifications, nucleic acid-based scaffolding and RNA-guided and DNA-controlled assembly of tubular RNA-encapsidating protein domains, yielding a novel class of 3D nucleoprotein architectures with polyvalent protein elements. In the long term, the production route might give rise to supramolecular systems with complex functionalities, installed via the orthogonal coupling of effector molecules to TLP domains.

Bottom-Up Assembly of TMV-Based Nucleoprotein Architectures on Solid Supports

RNA-guided self-assembly of tobacco mosaic virus (TMV)-like nucleoprotein nanotubes is possible using 3'-terminally surface-linked scaffold RNAs containing the viral origin of assembly (OAS). In combination with TMV coat protein (CP) preparations, these scaffold RNAs can direct the growth of selectively addressable multivalent carrier particles directly at sites of interest on demand. Serving as adapter templates for the installation of functional molecules, they may promote an integration of active units into miniaturized technical devices, or enable their presentation on soft-matter nanotube systems at high surface densities advantageous for, for example, biodetection or purification applications. This chapter describes all procedures essential for the bottom-up fabrication of "nanostar" colloids with gold cores and multiple TMV-like arms, immobilized in a programmable manner by way of hybridization of the RNA scaffolds to oligodeoxynucleotides exposed on the gold beads.

Semiconducting Hybrid Layer Fabrication Scaffolded by Virus Shells

The formation of virus-based semiconducting hybrid thin films is a two-step process, which involves assembly of virus particles as a template layer and subsequent selective mineralization of the virus surface with inorganic nanoparticles to build a semiconducting organic-inorganic hybrid film. Here, we present the use of the convective assembly technique to obtain homogeneous and dense template monolayers of wild-type tobacco mosaic virus (wt-TMV) and the TMV mutant E50Q, of which most particles do not have detectable amounts of RNA in the protein tube. On the top of the aligned virus layer, zinc oxide (ZnO) is deposited to prepare virus-ZnO semiconducting hybrid films with controllable thickness under mild conditions of the chemical bath deposition (CBD).

Dual Functionalization of Rod-Shaped Viruses on Single Coat Protein Subunits

Plant viruses are emerging as versatile tools for nanotechnology applications since it is possible to modify their multivalent protein surfaces and thereby introduce and display new functionalities. In this chapter, we describe a tobacco mosaic virus (TMV) variant that exposes two selectively addressable amino acid moieties on each of its 2130 coat protein (CP) subunits. A lysine as well as a cysteine introduced at accessible sites of every CP can be modified with amino- and/or thiol-reactive chemistry such as N-hydroxysuccinimide esters (NHS ester) and maleimide containing reagents alone or simultaneously. This enables the pairwise immobilization of distinct molecules in close vicinity to each other on the TMV surface by simple standard conjugation protocols. We describe the generation of the mutations, the virus propagation and isolation as well as the dual functionalization of the TMV variant with two fluorescent dyes. The labeling is evaluated by SDS-PAGE and spectrophotometry and the degree of labeling (DOL) calculated.

TMV-Templated Formation of Metal and Polymer Nanotubes

Metals and polymers are probably the most important construction materials, but also have many more functions, e.g., for electronics. The interaction of metal ions with tobacco mosaic virus (TMV) was originally used for the preparation of heavy metal isomorphic replacement for structural analysis. Metal ions can also be the precursors for metal clusters, particles, and layers. Various strategies have been developed, which allow the creation of metal layers on the external surface of TMV. Such layers can be made as metal tubes, enveloping a complete virion. An alternative strategy is adsorption of metal nanoparticles. If a dense coating of TMV is achieved, again a tube results. Nanoscale tubes have various physical properties that depend on size, crystallinity, uniformity, but especially on the nature of the metal. Polymer coatings are as yet rarely investigated, though they can be prepared quite easily.Here, a series of exemplary protocols is provided, which covers all of these different concepts.

RNA-Directed Assembly of Tobacco Mosaic Virus (TMV)-Like Carriers with Tunable Fractions of Differently Addressable Coat Proteins

Taking advantage of the ability for in vitro assembly of the plant-infecting virus tobacco mosaic virus (TMV), rod-shaped nanoscale scaffolds presenting different addressable groups can be obtained. We have established procedures resulting in virus-like particles with randomly distributed functional groups, with different groups arranged in striped but randomized structures, and even with distinct groups clustered in adjacent, better-defined domains. The TMV coat protein (CP) variants combined in these approaches can either originate all from TMV mutants propagated in planta, or be mixed with CP expressed in E. coli (CPEc). Protocols for expression and purification of a CPEc-His6 mutant in E. coli as well as the different methods for in vitro assembly and the visualization by decoration of one CP type are explained in detail.

Encapsulation of Inorganic Nanomaterials inside Virus-Based Nanoparticles for Bioimaging

Virus-based nanoparticles (VNPs) can serve as containers for inorganic nanomaterials with excellent physical and chemical properties. Incorporation of nanomaterials inside the inner cavity of VNPs has opened up lots of possibilities for imaging applications in the field of biology and medicine. Encapsulation of inorganic nanoparticles (NPs) in VNPs can achieve the labeling of VNPs with nanoprobes and maintain the original outer surface features of VNPs at the same time. In return, VNPs enhance the stability and biocompatibility of the inorganic cargoes. This review briefly summarizes the current typical strategies to encapsulate inorganic nanomaterials in VNPs, i.e. mineralization and self-assembly, as well as the applications of these hybrid nanostructures in the field of bioimaging, including in vitro and in vivo fluorescence imaging, magnetic resonance imaging, and theranostics. Nanophotonic studies based on the VNP platform are also discussed. We anticipate that this field will continue to flourish, with new exciting opportunities stemming from advancements in the rational design of VNPs, the development of excellent inorganic nanomaterials, the integration of multiple functionalities, and the regulation of nano-bio interfacial interactions.

Facile synthesis of ultrathin Ni-MOF nanobelts for high-efficiency determination of glucose in human serum

Ultrathin Ni-MOF nanobelts, [Ni₂₀(C₅H₆O₄)₂₀(H₂O)₈]·40H₂O(Ni-MIL-77 NBs), were synthesized by a facile one-pot solution process and can be used as an efficient catalyst electrode for glucose oxidation under alkaline conditions. Electrochemical measurements demonstrate that the NB/GCE, when used as a non-enzymatic glucose sensor, offers superior analytical performances with a wide linear range (from 1 μM to 500 μM), a low detection limit (0.25 μM, signal-to-noise = 3), and a response sensitivity of 1.542 μA mM^-1 cm^-2. Moreover, it can also be applied for glucose detection in human blood serum with the relative standard deviation (RSD) of 7.41%, showing the high precision of the sensor in measuring real samples.

Helical plant viral nanoparticles-bioinspired synthesis of nanomaterials and nanostructures

Viral nanotechnology is revolutionizing the biomimetic and bioinspired synthesis of novel nanomaterials. Bottom-up nanofabrication by self-assembly of individual molecular components of elongated viral nanoparticles (VNPs) and virus-like particles (VLPs) has resulted in the production of superior materials and structures in the nano(bio)technological fields. Viral capsids are attractive materials, because of their symmetry, monodispersity, and polyvalency. Helical VNPs/VLPs are unique prefabricated nanoscaffolds with large surface area to volume ratios and high aspect ratios, and enable the construction of exquisite supramolecular nanostructures. This review discusses the genetic and chemical modifications of outer, inner, and interface surfaces of a viral protein cage that will almost certainly lead to the development of superior next-generation targeted drug delivery and imaging systems, biosensors, energy storage and optoelectronic devices, therapeutics, and catalysts.

Virus-directed formation of electrocatalytically active nanoparticle-based Co3O4 tubes

Spinel-type Co₃O₄ finds applications in a wide range of fields, including clean energy conversion, where nanostructured Co₃O₄ may provide a cost-efficient alternative to platinum- and iridium-based catalysts for electrocatalytic water-splitting. We here describe a novel strategy in which basic cobalt carbonate - a precursor to Co₃O₄ - is precipitated as sheet-like structures and microspheres covered with fine surface protrusions, via ammonium carbonate decomposition at room temperature. Importantly, these mild reaction conditions enable us to employ bio-inspired templating approaches to further control the mineral structure. Rod-like tobacco mosaic viruses (TMV) were used as biotemplates for mineral deposition, where we profit from the ability of Co(ii) ions to mediate the ordered assembly of the virus nanorods to create complex tubular superstructures of TMV/ basic cobalt carbonate. Calcination of these tubules is then achieved with retention of the gross morphology, and generates a hierarchically-structured solid comprising interconnected Co₃O₄ nanoparticles. Evaluation of these Co₃O₄ materials as electrocatalysts for the oxygen evolution reaction (OER) demonstrates that the activity of Co₃O₄ prepared by calcination of ammonia diffusion-grown precursors in both, the absence or presence of TMV exceeds that of a commercial nanopowder.

Biogenic and Synthetic Peptides with Oppositely Charged Amino Acids as Binding Sites for Mineralization

Proteins regulate diverse biological processes by the specific interaction with, e.g., nucleic acids, proteins and inorganic molecules. The generation of inorganic hybrid materials, such as shell formation in mollusks, is a protein-controlled mineralization process. Moreover, inorganic-binding peptides are attractive for the bioinspired mineralization of non-natural inorganic functional materials for technical applications. However, it is still challenging to identify mineral-binding peptide motifs from biological systems as well as for technical systems. Here, three complementary approaches were combined to analyze protein motifs consisting of alternating positively and negatively charged amino acids: (i) the screening of natural biomineralization proteins; (ii) the selection of inorganic-binding peptides derived from phage display; and (iii) the mineralization of tobacco mosaic virus (TMV)-based templates. A respective peptide motif displayed on the TMV surface had a major impact on the SiO₂ mineralization. In addition, similar motifs were found in zinc oxide- and zirconia-binding peptides indicating a general binding feature. The comparative analysis presented here raises new questions regarding whether or not there is a common design principle based on acidic and basic amino acids for peptides interacting with minerals.

Virus-Templated Near-Amorphous Iron Oxide Nanotubes

We present a simple synthesis of iron oxide nanotubes, grown under very mild conditions from a solution containing Fe(II) and Fe(III), on rod-shaped tobacco mosaic virus templates. Their well-defined shape and surface chemistry suggest that these robust bionanoparticles are a versatile platform for synthesis of small, thin mineral tubes, which was achieved efficiently. Various characterization tools were used to explore the iron oxide in detail: Electron microscopy (SEM, TEM), magnetometry (SQUID-VSM), diffraction (XRD, TEM-SAED), electron spectroscopies (EELS, EDX, XPS), and X-ray absorption (XANES with EXAFS analysis). They allowed determination of the structure, crystallinity, magnetic properties, and composition of the tubes. The protein surface of the viral templates was crucial to nucleate iron oxide, exhibiting analogies to biomineralization in natural compartments such as ferritin cages.

Novel roles for well-known players: from tobacco mosaic virus pests to enzymatically active assemblies

The rod-shaped nanoparticles of the widespread plant pathogen tobacco mosaic virus (TMV) have been a matter of intense debates and cutting-edge research for more than a hundred years. During the late 19th century, their behavior in filtration tests applied to the agent causing the 'plant mosaic disease' eventually led to the discrimination of viruses from bacteria. Thereafter, they promoted the development of biophysical cornerstone techniques such as electron microscopy and ultracentrifugation. Since the 1950s, the robust, helically arranged nucleoprotein complexes consisting of a single RNA and more than 2100 identical coat protein subunits have enabled molecular studies which have pioneered the understanding of viral replication and self-assembly, and elucidated major aspects of virus-host interplay, which can lead to agronomically relevant diseases. However, during the last decades, TMV has acquired a new reputation as a well-defined high-yield nanotemplate with multivalent protein surfaces, allowing for an ordered high-density presentation of multiple active molecules or synthetic compounds. Amino acid side chains exposed on the viral coat may be tailored genetically or biochemically to meet the demands for selective conjugation reactions, or to directly engineer novel functionality on TMV-derived nanosticks. The natural TMV size (length: 300 nm) in combination with functional ligands such as peptides, enzymes, dyes, drugs or inorganic materials is advantageous for applications ranging from biomedical imaging and therapy approaches over surface enlargement of battery electrodes to the immobilization of enzymes. TMV building blocks are also amenable to external control of in vitro assembly and re-organization into technically expedient new shapes or arrays, which bears a unique potential for the development of 'smart' functional 3D structures. Among those, materials designed for enzyme-based biodetection layouts, which are routinely applied, e.g., for monitoring blood sugar concentrations, might profit particularly from the presence of TMV rods: Their surfaces were recently shown to stabilize enzymatic activities upon repeated consecutive uses and over several weeks. This review gives the reader a ride through strikingly diverse achievements obtained with TMV-based particles, compares them to the progress with related viruses, and focuses on latest results revealing special advantages for enzyme-based biosensing formats, which might be of high interest for diagnostics employing 'systems-on-a-chip'.

New Strategies and Methods to Study Interactions between Tobacco Mosaic Virus Coat Protein and Its Inhibitors

Studies of the targets of anti-viral compounds are hot topics in the field of pesticide research. Various efficient anti-TMV (Tobacco Mosaic Virus) compounds, such as Ningnanmycin (NNM), Antofine (ATF), Dufulin (DFL) and Bingqingxiao (BQX) are available. However, the mechanisms of the action of these compounds on targets remain unclear. To further study the mechanism of the action of the anti-TMV inhibitors, the TMV coat protein (TMV CP) was expressed and self-assembled into four-layer aggregate disks in vitro, which could be reassembled into infectious virus particles with TMV RNA. The interactions between the anti-TMV compounds and the TMV CP disk were analyzed by size exclusion chromatography, isothermal titration calorimetry and native-polyacrylamide gel electrophoresis methods. The results revealed that assembly of the four-layer aggregate disk was inhibited by NNM; it changed the four-layer aggregate disk into trimers, and affected the regular assembly of TMV CP and TMV RNA. The four-layer aggregate disk of TMV CP was little inhibited by ATF, DFL and BQX. Our results provide original data, as well as new strategies and methods, for research on the mechanism of action of anti-viral drugs.

Modified TMV Particles as Beneficial Scaffolds to Present Sensor Enzymes

Tobacco mosaic virus (TMV) is a robust nanotubular nucleoprotein scaffold increasingly employed for the high density presentation of functional molecules such as peptides, fluorescent dyes, and antibodies. We report on its use as advantageous carrier for sensor enzymes. A TMV mutant with a cysteine residue exposed on every coat protein (CP) subunit (TMVCys) enabled the coupling of bifunctional maleimide-polyethylene glycol (PEG)-biotin linkers (TMVCys/Bio). Its surface was equipped with two streptavidin [SA]-conjugated enzymes: glucose oxidase ([SA]-GOx) and horseradish peroxidase ([SA]-HRP). At least 50% of the CPs were decorated with a linker molecule, and all thereof with active enzymes. Upon use as adapter scaffolds in conventional "high-binding" microtiter plates, TMV sticks allowed the immobilization of up to 45-fold higher catalytic activities than control samples with the same input of enzymes. Moreover, they increased storage stability and reusability in relation to enzymes applied directly to microtiter plate wells. The functionalized TMV adsorbed to solid supports showed a homogeneous distribution of the conjugated enzymes and structural integrity of the nanorods upon transmission electron and atomic force microscopy. The high surface-increase and steric accessibility of the viral scaffolds in combination with the biochemical environment provided by the plant viral coat may explain the beneficial effects. TMV can, thus, serve as a favorable multivalent nanoscale platform for the ordered presentation of bioactive proteins.

Peptide-equipped tobacco mosaic virus templates for selective and controllable biomineral deposition

The coating of regular-shaped, readily available nanorod biotemplates with inorganic compounds has attracted increasing interest during recent years. The goal is an effective, bioinspired fabrication of fiber-reinforced composites and robust, miniaturized technical devices. Major challenges in the synthesis of applicable mineralized nanorods lie in selectivity and adjustability of the inorganic material deposited on the biological, rod-shaped backbones, with respect to thickness and surface profile of the resulting coating, as well as the avoidance of aggregation into extended superstructures. Nanotubular tobacco mosaic virus (TMV) templates have proved particularly suitable towards this goal: Their multivalent protein coating can be modified by high-surface-density conjugation of peptides, inducing and governing silica deposition from precursor solutions in vitro. In this study, TMV has been equipped with mineralization-directing peptides designed to yield silica coatings in a reliable and predictable manner via precipitation from tetraethoxysilane (TEOS) precursors. Three peptide groups were compared regarding their influence on silica polymerization: (i) two peptide variants with alternating basic and acidic residues, i.e. lysine-aspartic acid (KD) x motifs expected to act as charge-relay systems promoting TEOS hydrolysis and silica polymerization; (ii) a tetrahistidine-exposing polypeptide (CA4H4) known to induce silicification due to the positive charge of its clustered imidazole side chains; and (iii) two peptides with high ZnO binding affinity. Differential effects on the mineralization of the TMV surface were demonstrated, where a (KD) x charge-relay peptide (designed in this study) led to the most reproducible and selective silica deposition. A homogenous coating of the biotemplate and tight control of shell thickness were achieved.

Site-selective nucleation and controlled growth of gold nanostructures in tobacco mosaic virus nanotubulars

Site-selective biomineralization of Au nanostructures in the interior channel of Tobacco Mosaic Virus (TMV) is achieved by mutating threonine 103 in TMV to cysteine (T103C-TMV) to introduce the strong coordination interaction between the arrayed sulfhydryl ligands and gold species. By finely tuning the reaction conditions, Au nanoparticle chains and Au nanorods are successfully and exclusively synthesized inside the T103C-TMV nanotubes.

Genetically improved monolayer-forming tobacco mosaic viruses to generate nanostructured semiconducting bio/inorganic hybrids

The genetically determined design of structured functional bio/inorganic materials was investigated by applying a convective assembly approach. Wildtype tobacco mosaic virus (wt TMV) as well as several TMV mutants were organized on substrates over macroscopic-length scales. Depending on the virus type, the self-organization behavior showed pronounced differences in the surface arrangement under the same convective assembly conditions. Additionally, under varying assembly parameters, the virus particles generated structures encompassing morphologies emerging from single micrometer long fibers aligned parallel to the triple-contact line through disordered but dense films to smooth and uniform monolayers. Monolayers with diverse packing densities were used as templates to form TMV/ZnO hybrid materials. The semiconducting properties can be directly designed and tuned by the variation of the template architecture which are reflected in the transistor performance.

RNA-controlled assembly of tobacco mosaic virus-derived complex structures: from nanoboomerangs to tetrapods

The in vitro assembly of artificial nanotubular nucleoprotein shapes based on tobacco mosaic virus-(TMV-)-derived building blocks yielded different spatial organizations of viral coat protein subunits on genetically engineered RNA molecules, containing two or multiple TMV origins of assembly (OAs). The growth of kinked nanoboomerangs as well as of branched multipods was determined by the encapsidated RNAs. A largely simultaneous initiation at two origins and subsequent bidirectional tube elongation could be visualized by transmission electron microscopy of intermediates and final products. Collision of the nascent tubes' ends produced angular particles with well-defined arm lengths. RNAs with three to five OAs generated branched multipods with a maximum of four arms. The potential of such an RNA-directed self-assembly of uncommon nanotubular architectures for the fabrication of complex multivalent nanotemplates used in functional hybrid materials is discussed.

Production and applications of engineered viral capsids

As biological agents, viruses come in an astounding range of sizes, with varied shapes and surface morphologies. The structures of viral capsids are generally assemblies of hundreds of copies of one or a few proteins which can be harnessed for use in a wide variety of applications in biotechnology, nanotechnology, and medicine. Despite their complexity, many capsid types form as homogenous populations of precise geometrical assemblies. This is important in both medicine, where well-defined therapeutics are critical for drug performance and federal approval, and nanotechnology, where precise placement affects the properties of the desired material. Here we review the production of viruses and virus-like particles with methods for selecting and manipulating the size, surface chemistry, assembly state, and interior cargo of capsid. We then discuss many of the applications used in research today and the potential commercial and therapeutic products from engineered viral capsids.

Fabrication of nanoarchitectures templated by virus-based nanoparticles: strategies and applications

Biomolecular nanostructures in nature are drawing increasing interests in the field of materials sciences. As a typical group of them, virus-based nanoparticles (VNPs), which are nanocages or nanorods assembled from capsid proteins of viruses, have been widely exploited as templates to guide the fabrication of complex nanoarchitectures (NAs), because of their appropriate sizes (ca. 20-200 nm), homogeneity, addressable functionalization, facile modification via chemical and genetic routes, and convenient preparation. Foreign materials can be positioned in the inner cavity or on the outer surface of VNPs, through either direct synthesis or assembling preformed nanomaterials. Simultaneous use of the inner and outer space of VNPs facilitates integration of multiple functionalities in a single NA. This review briefly summarizes the strategies for fabrication of NAs templated by VNPs and wide applications of these NAs in fields of catalysis, energy, biomedicine, and nanophotonics, etc.

The condensation of water on adsorbed viruses

The wetting and dewetting behavior of biological nanostructures and to a greater degree single molecules is not well-known even though their contact with water is the basis for all biology. Here, we show that environmental electron microscopy (EM) can be applied as a means of imaging the condensation of water onto viruses. We captured the formation of submicrometer water droplets and filaments on single viral particles by environmental EM and by environmental transmission EM. The condensate structures are compatible with capillary condensation between adsorbed virus particles and with known droplet shapes on patterned surfaces. Our results confirm that such droplets exist down to <50 nm. The viruses preserved their shape after a condensation/evaporation cycle as expected from their stability in air and water. Moreover we developed procedures that overcome problems of beam damage and of resolving structures with a low atomic number.

Crystal structure of a four-layer aggregate of engineered TMV CP implies the importance of terminal residues for oligomer assembly

Background

Crystal structures of the tobacco mosaic virus (TMV) coat protein (CP) in its helical and disk conformations have previously been determined at the atomic level. For the helical structure, interactions of proteins and nucleic acids in the main chains were clearly observed; however, the conformation of residues at the C-terminus was flexible and disordered. For the four-layer aggregate disk structure, interactions of the main chain residues could only be observed through water–mediated hydrogen bonding with protein residues. In this study, the effects of the C-terminal peptides on the interactions of TMV CP were investigated by crystal structure determination.

Methodology/Principal Findings

The crystal structure of a genetically engineered TMV CP was resolved at 3.06 Å. For the genetically engineered TMV CP, a six-histidine (His) tag was introduced at the N-terminus, and the C-terminal residues 155 to 158 were truncated (N-His-TMV CP¹⁹). Overall, N-His-TMV CP¹⁹ protein self-assembled into the four-layer aggregate form. The conformations of residues Gln36, Thr59, Asp115 and Arg134 were carefully analyzed in the high radius and low radius regions of N-His-TMV CP¹⁹, which were found to be significantly different from those observed previously for the helical and four-layer aggregate forms. In addition, the aggregation of the N-His-TMV CP¹⁹ layers was found to primarily be mediated through direct hydrogen-bonding. Notably, this engineered protein also can package RNA effectively and assemble into an infectious virus particle.

Conclusion

The terminal sequence of amino acids influences the conformation and interactions of the four-layer aggregate. Direct protein–protein interactions are observed in the major overlap region when residues Gly155 to Thr158 at the C-terminus are truncated. This engineered TMV CP is reassembled by direct protein–protein interaction and maintains the normal function of the four-layer aggregate of TMV CP in the presence of RNA.