Baculovirus

The Baculoviridae family ( baculovirus ) includes double-stranded, circular DNA viruses filamentous. They infect only invertebrates, their main host are moth larvae, but more than 600 hosts are described. Baculoviruses are used in genetic engineering to produce complex Eukaryotenproteinen in cell cultures as well as to Vektorklonierung. Also, they are used in agriculture for the control of insect pests.

The name " Baculo " comes from Latin baculum = floor, bar and refers to the morphology of the nucleocapsid. Within the family, two genera were formerly distinguished: nucleopolyhedrovirus (NPV) and granulovirus (GV, now genus Betabaculovirus ). In Betabaculovirus comes only a nucleocapsid, come in from the genus nucleopolyhedrovirus newly subdivided genera alpha, gamma and Deltabaculovirus either individual ( SNPV ) or more ( MNPV ) nucleocapsids per case per case before. The virions ( nucleocapsid and envelope) are now again in a granulin (GV ) - or polyhedrin (NPV ) matrix embedded. The Betabaculoviren have only one virion per Granulinmatrix in other genres multiple virions are Polyhedrinmatrix.

Dissemination

They are found worldwide and were first described in the 16th century, when " Welkkrankeit " in silkworms. In the 1940s they were used as biopesticides in crop fields to decimate insect pests. However, subsequent studies they were used in the 1990s for the production of eukaryotic proteins, as they can be propagated in cell cultures easily. The viruses are adapted to invertebrates with over 600 potential host species. Mainly they attacked moth larvae, but they were also found in plants, wasps, mosquitoes, and shrimp.

Life cycle

In its life cycle, the virus comes in two forms, the ODV ( Occlusion Derived Virus), with protein shell, and the BV ( Budding virus). The ODV form is necessary for the initial infection and later BV particles are formed.

The main infection proceeds via contaminated leaves, which are eaten by insects. The virus enters into the digestive tract, where the protein coat (ODV form) is dissolved due to the basic environment. The free virus now attach themselves to the intestinal epithelial cells and are taken up by endocytosis into an endosome, from which they escape and are now transported as nucleocapsids, presumably through actin filaments in the cell nucleus. Here, the replication of the virus. Now non-enveloped viruses (BV ) are generated and the virus infects the surrounding ( basolateral ) epithelial cells. However, the BV particles envelop also loose with cell membrane containing the viral glycoproteins.

The infection can be divided into three phases: the early phase (0-6 hours), the late phase ( 24 6 ) and the very late phase (18-24 to 72 h after the infection). Until the late phase is non-enveloped BV forms are released in the last phase but only ODV forms budding through the nuclear membrane and form filled with virus particles, which are filled with OB ( occlusion body ) protein. These now have a greater resistance to environmental factors than the BV form and for the dissemination of the virus to the next host. Since the exit of the virus, the cell is lysed, it is the entire insect into a regular liquefaction, only the chitin remains intact. These bursts later and spread the virus to the leaf surface. This property was caused by this viral disease also the English name " wilting disease" ( Welkkrankheit ).

Structure of the virion

The best-studied baculovirus is Autographa californica nucleopolyhedrovirus multicapsid ( AcMNPV ). It was first isolated from a Gammaeulenart ( Autographa californica ), who lives on alfalfa. The genome has 134 kbp (kilo base pairs) and has 154 ORF. Capsid protein VP39 is the most important, it is with some of the smaller proteins, the nucleocapsid (21 nm x 260 nm), which encloses the DNA which in turn is surrounded by the protein p6.9.

BV particles need for an infection, the glycoprotein gp64 ( gene 64), which occurs at the ends of the filamentous virions. This protein is not found in the ODV particles, there are some proteins are unique to ODV. There are also differences in the composition of lipids of the envelope, at BV occurs phosphatidylserine, ODV contains phosphatidylcholine and phosphatidylethanolamine.

Envelope protein gp64

Over the evolution of the virus has changed the gp64. Ld139 (also baculovirus F- protein) of the gypsy moth Lymantria dispar ( LdMNPV ) is probably an original membrane fusion protein ( to release the virus from the host cell) which has been replaced by the gp64 as do not " equivalent " protein because Ld139 and gp64 in the genome many baculovirus species occur ( silkworm, Gammaeule, Douglas brush Spinner (family Trägspinner ) ).

Gp64 itself is a homotrimeric protein that sits at the poles of filamentous BV particles. It consists of 512 amino acids, with four glycosylation sites at asparagine residues and an N-terminal signal sequence of 20 amino acids and fusion further oligomerization domains as well as a hydrophobic transmembrane domain at the C -terminal seven amino acids. It is formed in the early and in the late phase of infection with a maximum after 24 to 26 hours after infection. The trimerization ( assembly of gp64 per 3 units) via internal cystine bonds is important for the transport to the cell surface, since only 33 percent of the gp64 reach the surface and monomers are degraded within the cell.

This protein is essential for the budding of virions from the cell, as well as for the infection of other cells in the infection cycle. Its main task is regulated by the pH value fusion with the endosome. Although gp64 is required for virus replication, mutants which lack gp64, virus be made to work again on substitution with LD130, or the G-protein of the " Vesicular stomatitis ".

System

• Family Baculoviridae

• Genus Alphabaculovirus
• Genus Betabaculovirus
• Genus Gammabaculovirus
• Genus Deltabaculovirus

Swell

• Virus family