Baculoviridae

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Baculoviridae
Virus classification Red Pencil Icon.png
(unranked): Virus
Phylum: incertae sedis
Class: incertae sedis
Order: incertae sedis
Family:Baculoviridae
Genera

Alphabaculovirus
Betabaculovirus
Deltabaculovirus
Gammabaculovirus

Contents

Baculoviridae is a family of viruses. Arthropods, lepidoptera, hymenoptera, diptera, and decapoda serve as natural hosts. There are currently 76 species in this family, divided among 4 genera. [1] [2] [3]

Virus Type of non-cellular infectious agent

A virus is a small infectious agent that replicates only inside the living cells of an organism. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.

Arthropod Phylum of invertebrates

An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda, which includes insects, arachnids, myriapods, and crustaceans. The term Arthropoda as originally proposed refers to a proposed grouping of Euarthropods and the phylum Onychophora.

Lepidoptera Order of insects including moths and butterflies

Lepidoptera is an order of insects that includes butterflies and moths. About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 per cent of the total described species of living organisms. It is one of the most widespread and widely recognizable insect orders in the world. The Lepidoptera show many variations of the basic body structure that have evolved to gain advantages in lifestyle and distribution. Recent estimates suggest the order may have more species than earlier thought, and is among the four most speciose orders, along with the Hymenoptera, Diptera, and Coleoptera.

Baculoviruses are known to infect invertebrates, with over 600 host species having been described. Immature (larval) forms of moth species are the most common hosts, but these viruses have also been found infecting sawflies, mosquitoes, and shrimp. Although baculoviruses are capable of entering mammalian cells in culture [4] they are not known to be capable of replication in mammalian or other vertebrate animal cells.

Invertebrate Animals without a vertebrate column

Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord. This includes all animals apart from the subphylum Vertebrata. Familiar examples of invertebrates include arthropods, mollusks, annelids, and cnidarians.

Moth Group of mostly-nocturnal insects in the order Lepidoptera

Moths are a polyphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of which have yet to be described. Most species of moth are nocturnal, but there are also crepuscular and diurnal species.

Sawfly suborder of insects

Sawflies are the insects of the suborder Symphyta within the order Hymenoptera alongside ants, bees and wasps. The common name comes from the saw-like appearance of the ovipositor, which the females use to cut into the plants where they lay their eggs. The name is associated especially with the Tenthredinoidea, by far the largest superfamily, with about 7,000 known species; in the entire suborder, there are 8,000 described species in more than 800 genera. The suborder Symphyta is paraphyletic, consisting of several basal groups within the order Hymenoptera.

Starting in the 1940s they were used and studied widely as biopesticides in crop fields. Baculoviruses contain circular double-stranded genome ranging from 80 to 180 kbp.

Biopesticides, a contraction of 'biological pesticides', include several types of pest management intervention: through predatory, parasitic, or chemical relationships. The term has been associated historically with [biological control] – and by implication – the manipulation of living organisms. Regulatory positions can be influenced by public perceptions, thus:

Historical influence

The earliest records of baculoviruses can be found in the literature from as early as the sixteenth century in reports of "wilting disease" infecting silk-producing larva. Starting in the 1940s they were used and studied widely as biopesticides in crop fields. Since the 1990s they have been utilized for producing complex eukaryotic proteins in insect cell cultures (see Sf21, High Five cells). These recombinant proteins have been used in research and as vaccines in both human and veterinary medical treatments (for example, the most widely used vaccine for prevention of H5N1 avian influenza in chickens was produced in a baculovirus expression vector). More recently it has been found that baculoviruses can transduce mammalian cells with a suitable promoter. [5] These medical and potential medical uses have accelerated the number of publications on baculoviruses since 1995.

Silk fine, lustrous, natural fiber produced by the larvae of various silk moths, especially the species Bombyx mori

Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity (sericulture). The shimmering appearance of silk is due to the triangular prism-like structure of the silk fibre, which allows silk cloth to refract incoming light at different angles, thus producing different colors.

Protein Biological molecule consisting of chains of amino acid residues

Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific three-dimensional structure that determines its activity.

Cell culture process by which cells are grown under controlled conditions

Cell culture is the process by which cells are grown under controlled conditions, generally outside their natural environment. After the cells of interest have been isolated from living tissue, they can subsequently be maintained under carefully controlled conditions. These conditions vary for each cell type, but generally consist of a suitable vessel with a substrate or medium that supplies the essential nutrients (amino acids, carbohydrates, vitamins, minerals), growth factors, hormones, and gases (CO2, O2), and regulates the physio-chemical environment (pH buffer, osmotic pressure, temperature). Most cells require a surface or an artificial substrate (adherent or monolayer culture) whereas others can be grown free floating in culture medium (suspension culture). The lifespan of most cells is genetically determined, but some cell culturing cells have been “transformed” into immortal cells which will reproduce indefinitely if the optimal conditions are provided.

Baculovirus life cycle

Diagram of a NPV life cycle Npv-life cycle-en.jpg
Diagram of a NPV life cycle

The baculovirus life cycle involves two distinct forms of virus. Occlusion derived virus (ODV) is present in a protein matrix (polyhedrin or granulin) and is responsible for the primary infection of the host while the budded virus (BV) is released from the infected host cells later during the secondary infection.

Baculoviruses have very species-specific tropisms among the invertebrates with over 700 host species having been described. Immature (larval) forms of moth species are the most common hosts, but these viruses have also been found infecting sawflies, mosquitoes, and shrimp.

Mosquito Family of flies

Mosquitoes are a group of about 3,500 species of small insects that are flies. Within Diptera they constitute the family Culicidae. The word "mosquito" is Spanish for "little fly". Mosquitoes have a slender segmented body, one pair of wings, three pairs of long hair-like legs, feathery antennae, and elongated mouthparts.

Shrimp Decapod crustaceans

The term shrimp is used to refer to some decapod crustaceans, although the exact animals covered can vary. Used broadly, shrimp may cover any of the groups with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata. In some fields, however, the term is used more narrowly and may be restricted to Caridea, to smaller species of either group or to only the marine species. Under the broader definition, shrimp may be synonymous with prawn, covering stalk-eyed swimming crustaceans with long narrow muscular tails (abdomens), long whiskers (antennae), and slender legs. Any small crustacean which resembles a shrimp tends to be called one. They swim forward by paddling with swimmerets on the underside of their abdomens, although their escape response is typically repeated flicks with the tail driving them backwards very quickly. Crabs and lobsters have strong walking legs, whereas shrimp have thin, fragile legs which they use primarily for perching.

Typically, the initial infection occurs when a susceptible host insect feeds on plants that are contaminated with the occluded form of the virus. The protein matrix dissolves in the alkaline environment of the host midgut (stomach), releasing ODV that then fuse to the columnar epithelial cell membrane of the host intestine and are taken into the cell in endosomes. Nucleocapsids escape from the endosomes and are transported to nucleus. This step is possibly mediated by actin filaments. Viral transcription and replication occur in the cell nucleus and new BV particles are budded out from the basolateral side to spread the infection systemically. During budding, BV acquires a loosely fitting host cell membrane with expressed and displayed viral glycoproteins.

Baculovirus infection can be divided to three distinct phases:

While BV is produced in the late phase, the ODV form is produced in the very late phase acquiring the envelope from host cell nucleus and embedded in the matrix of occlusion body protein. These occlusion bodies are released when cells lyse to further spread baculovirus infection to next host. The extensive lysis of cells frequently causes the host insect to literally disintegrate, thus the reason for the historic name "wilting disease." The complete ODV-polyhedrin particles are resistant to heat and light inactivation, whereas the naked BV virion is more sensitive to environment.

When infecting a caterpillar, the advanced stages of infection cause the host to feed without resting, and then to climb to the higher parts of trees, including exposed places they would normally avoid due to the risk of predators. This is an advantage for the virus if (when the host dissolves) it can drip down onto leaves which will be consumed by new hosts. [6]

Structure of the virion

Diagram of a Nucleopolyhedrovirus Nucleopolyhedrovirus.jpg
Diagram of a Nucleopolyhedrovirus

The most studied baculovirus is Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV). The virus was originally isolated from the alfalfa looper (a lepidopteran) and contains a 134-kbp genome with 154 open reading frames (ORF). The major capsid protein VP39 together with some minor proteins forms the nucleocapsid (21 nm x 260 nm) that encloses the DNA with p6.9 protein.

BV acquires its envelope from the cell membrane and requires a glycoprotein, gp64, to be able to spread systemic infection. This protein forms structures called peplomers on one end of the budded virus particle but is not found on ODV (although several other proteins are only associated with the ODV form). Some differences also exist in the lipid composition of the viral envelope of the two forms. While the BV envelope consists of phosphatidylserine, ODV contains phosphatidylcholine and phosphatidylethanolamine.

A nucleocapsid assembly-essential element (NAE) was identified in the AcMNPV genome. The NAE is an internal cis-element within the ac83 gene. The nucleocapsid assembly is not dependent on the Ac83 protein product. [7]

Major envelope glycoprotein gp64

During periods of evolution, the baculoviral envelope glycoproteins have undergone changes. Ld130, also known as baculovirus F-protein from Lymantria dispar (LdMNPV) is suggested to be an ancestral envelope fusion protein which has been replaced by non-orthologous gene replacement with gp64 in AcMNPV, Bombyx mori (BmNPV) and Orgyia pseudotsugata (OpMNPV) while they still retain the ld130 gene.

Gp64 is a homotrimeric membrane glycoprotein which is polarly present on the rod-shaped virion. It consists of 512 amino acids (aa) with four glycosylation sites at asparagine residues and has a N-terminal signal sequence (20 aa), oligomerization and fusion domain and a hydrophobic transmembrane domain near the C-terminus (7 aa).

It is produced in both early and late phases of the infection cycle with a maximal rate of synthesis occurring in 24–26 h p.i.. Trimerization with intermolecular cysteine-bonds seems to be a crucial step for protein transport to cell surface, since only 33% of synthesized protein reaches cell surface as monomeric gp64 is degraded within the cells.

Gp64 is essential for efficient budding of the virion and for the cell-to-cell transmission during the infection cycle as well as viral entry i.e. causing viral trophism and endosome mediated uptake to the cell. The major function of the gp64 envelope protein is to cause the pH-mediated envelope fusion to the endosome. Although gp64 has variety of essential functions, it has been reported that gp64-null baculoviruses can be substituted with other viral glycoproteins such as Ld130, G-protein of Vesicular stomatitis virus. These substitutions will result in functional virons.

Applications

Baculovirus expression in insect cells represents a robust method for producing recombinant glycoproteins or membrane proteins. [8] [9] [10] Baculovirus-produced proteins are currently under study as therapeutic cancer vaccines with several immunologic advantages over proteins derived from mammalian sources. [11]

Biosafety

Baculoviruses are incapable of replicating within the cells of mammals and plants. [12] They have a restricted range of hosts that they can infect that is typically restricted to a limited number of closely related insect species. Because baculoviruses are not harmful to humans, they are considered a safe option for use in research applications. They are also used as biological agents as in the case of the Indian mealmoth, a grain-feeding pest. [13]

Taxonomy

The name of this family has been derived from the latin word baculus, meaning stick. The family has been divided into four genera: Alphabaculovirus (lepidopteran-specific nucleopolyhedroviruses), Betabaculovirus (lepidopteran-specific Granuloviruses), Gammabaculovirus (hymenopteran-specific nucleopolyhedroviruses) and Deltabaculovirus (dipteran-specific nucleopolyhedroviruses). [14]

Group: dsDNA

[15]

Evolution

Baculoviruses are thought to have evolved from the Nudivirus family of viruses 310  million years ago. [16]

See also

Related Research Articles

<i>Paramyxoviridae</i> viruses of the Paramyxoviridae family, responsible for a number of human and animal diseases

Paramyxoviridae is a family of viruses in the order Mononegavirales. Vertebrates serve as natural hosts; no known plants serve as vectors. Currently, 72 species are placed in this family, divided among 14 genera. Diseases associated with this negative-sense, single-stranded RNA virus family include measles, mumps, and respiratory tract infections.

Epstein–Barr virus Virus of the herpes family

The Epstein–Barr virus, formally called Human gammaherpesvirus 4, is one of eight known human herpesvirus types in the herpes family, and is one of the most common viruses in humans.

<i>Indiana vesiculovirus</i> species of virus

Indiana vesiculovirus, formerly Vesicular stomatitis Indiana virus is a virus in the family Rhabdoviridae; the well-known Rabies lyssavirus belongs to the same family. VSIV can infect insects, cattle, horses and pigs. It has particular importance to farmers in certain regions of the world where it infects cattle. This is because its clinical presentation is identical to the very important foot and mouth disease virus.

Rabies virus species of virus

Rabies lyssavirus, formerly Rabies virus, is a neurotropic virus that causes rabies in humans and animals. Rabies transmission can occur through the saliva of animals and less commonly through contact with human saliva. Rabies lyssavirus, like many rhabdoviruses, has an extremely wide host range. In the wild it has been found infecting many mammalian species, while in the laboratory it has been found that birds can be infected, as well as cell cultures from mammals, birds, reptiles and insects.

Mardivirus is a genus of viruses in the order Herpesvirales, in the family Herpesviridae, in the subfamily Alphaherpesvirinae. Chickens, turkeys, and quail serve as natural hosts. There are currently five species in this genus including the type species Gallid herpesvirus 2. Diseases associated with this genus include: Marek's disease, which causes asymmetric paralysis of one or more limbs, neurological symptoms, and development of multiple lymphomas that manifest as solid tumors. Gallid herpesvirus 2 is the only one of these viruses known to be pathogenic and due to the antigenic similarity between the three viruses the other two have been used to vaccinate against Marek’s disease. These viruses have double stranded DNA genomes with no RNA intermediate.

<i>Alphavirus</i> genus of viruses

In biology and immunology, an Alphavirus belongs to group IV of the Baltimore classification of the Togaviridae family of viruses, according to the system of classification based on viral genome composition introduced by David Baltimore in 1971. Alphaviruses, like all other group IV viruses, have a positive sense, single-stranded RNA genome. There are thirty alphaviruses able to infect various vertebrates such as humans, rodents, fish, birds, and larger mammals such as horses as well as invertebrates. Transmission between species and individuals occurs mainly via mosquitoes, making the alphaviruses a member of the collection of arboviruses – or arthropod-borne viruses. Alphavirus particles are enveloped, have a 70 nm diameter, tend to be spherical, and have a 40 nm isometric nucleocapsid.

<i>Thogotovirus</i> genus of viruses

Thogotovirus is a genus of enveloped RNA viruses, one of seven genera in the virus family Orthomyxoviridae. Their single-stranded, negative-sense RNA genome has six or seven segments. Thogotoviruses are distinguished from most other orthomyxoviruses by being arboviruses – viruses that are transmitted by arthropods, in this case usually ticks. Thogotoviruses can replicate in both tick cells and vertebrate cells; one subtype has also been isolated from mosquitoes. A consequence of being transmitted by blood-sucking vectors is that the virus must spread systemically in the vertebrate host – unlike influenza viruses, which are transmitted by respiratory droplets and are usually confined to the respiratory system.

Argentinian mammarenavirus, formerly Junin virus or Junín virus, is a Mammarenavirus that causes Argentine hemorrhagic fever (AHF). The virus took its original name from the city of Junín, around which the first cases of infection were reported, in 1958.

Env is a viral gene that encodes the protein forming the viral envelope. The expression of the env gene enables retroviruses to target and attach to specific cell types, and to infiltrate the target cell membrane.

Ascoviridae is a family of double strand DNA viruses that infect primarily invertebrates, mainly noctuids and spodoptera species; it contains two genera, Ascovirus, which contains three species, and Toursvirus with a single species Diadromus pulchellus toursvirus. The type species of Ascovirus is Spodoptera frugiperda ascovirus 1a, which infects the army worm.

Entomopoxvirinae is a subfamily of viruses, in the family Poxviridae. Insects, human, vertebrates, and arthropods serve as natural hosts. There are currently 31 species in this subfamily, divided among 3 genera. Diseases associated with this subfamily include: impairment of motility and development.

<i>Zaire ebolavirus</i> Species of virus affecting humans and animals

Zaire ebolavirus, more commonly known as simply Ebola virus (EBOV), is one of six known species within the genus Ebolavirus. Four of the six known ebolaviruses, including EBOV, cause a severe and often fatal hemorrhagic fever in humans and other mammals, known as Ebola virus disease (EVD). Ebola virus has caused the majority of human deaths from EVD and is the cause of the 2013–2016 Ebola virus epidemic in West Africa, which resulted in at least 28,646 suspected cases and 11,323 confirmed deaths.

Batai virus (BATV) is a RNA virus belonging to order Bunyavirales, genus Orthobunyavirus.

Early 35 kDa protein

The Early 35 kDa protein, or P35 in short, is a baculoviral protein that inhibits apoptosis in the cells infected by the virus. Although baculoviruses infect only invertebrates in nature, ectopic expression of P35 in vertebrate animals and cells also results in inhibition of apoptosis, thus indicating a universal mechanism. P35 has been shown to be a caspase inhibitor with a very wide spectrum of activity both in regard to inhibited caspase types and to species in which the mechanism is conserved.

Alphabaculovirus is a genus of viruses in the family Baculoviridae. Its natural hosts include a wide range of invertebrates, among them winged insects, Lepidopterans, Hymenopterans, Dipterans, and decapods. There are currently 47 species in the genus, including the type species Autographa californica multiple nucleopolyhedrovirus.

Betabaculovirus genus of viruses

Betabaculovirus is a genus of viruses, in the family Baculoviridae. Arthropods serve as natural hosts. There are currently 26 species in this genus including the type species Cydia pomonella granulovirus.

Deltabaculovirus is a genus of viruses, in the family Baculoviridae. Mosquito larvae serve as natural hosts. There is currently only one species in this genus: the type species Culex nigripalpus nucleopolyhedrovirus'.

Gammabaculovirus is a genus of viruses, in the family Baculoviridae. Hymenoptera serve as natural hosts. There are currently only two species in this genus including the type species Neodiprion lecontei nucleopolyhedrovirus.

<i>Pneumoviridae</i> Family of viruses

Pneumoviridae is a new virus family in the order Mononegavirales. It was created in 2016 by elevating the now dissolved paramyxoviral subfamily Pneumovirinae. Natural hosts include humans, cattle, and rodents. There are currently 5 species in the Pneumoviridae family, divided between 2 genera. Pneumoviruses are pleomorphic, capable of producing spherical and filamentous enveloped virions that vary in size from 150 to 200 nm in diameter. The nucleocapsid consisting of a protein shell and viral nucleic acids has a helical symmetry. Nucleocapsids have a diameter of 13.5 nm and a helical pitch of 6.5 nm. The genome is composed of negative-sense single-stranded RNA that is non-segmented. It is about 15kb in size, and encodes 11 proteins. A unique feature of the genome is the M2 gene, which encodes proteins M2-1 and M2-2. The Pneumoviridae M2-1 protein is distinctive, and no homologue has been found in any other virus families. It functions as a processivity factor for the virus RNA-dependent RNA polymerase, and promotes viral RNA synthesis. Viruses in this family are often associated with respiratory infections, and are transmitted through respiratory secretions.

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is a nucleopolyhedrovirus belonging to the family Baculoviridae.

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Further reading