Viruses lipoprotein envelope

Spontaneous fusion of cultured cells occurs only rarely. However, the rate at which it happens can be markedly increased by the addition of certain viruses or chemical fusogens to the culture. Sendai virus, as used in early somatic cell fusions, has a lipoprotein envelope similar in structure to the animal cell membrane. It has been suggested that a glycoprotein in the envelope promotes cell fusion by an as yet unexplained mechanism. 

Figure A10.1 A schematic representation of the structure of a virus (a) without a lipoprotein envelope and (b) with a lipoprotein envelope...

The genome in influenza A and B types is enclosed within an outer lipoprotein envelope (Fig. 17.1). The Ml protein lines the inside of the envelope and is chemically bound to the ribonucleoprotein [14], The Ml protein plays an important role in the mediation of nuclear export of viral ribonucleoproteins and also in virus assembly and budding during the infectious cycle [5, 14, 15], An antigenic protein M2, which functions as a proton-selective ion channel, is present in the viral membrane of influenza A viruses [6, 13], In influenza B, the ion channel activity to aid virus uncoating in the endosome is carried out by the similar integral membrane protein BM2 [11],... 

In addition to the protein coat, many animal virus particles are surrounded by a lipoprotein envelope which has generally been derived from the cytoplasmic membrane of their last host cell. 

A study on the effects of bond reducing chemicals on viruses [16] investigated the susceptibility of vims inactivation to dithiothreitol (DTT), a disulfide bond reducing agent. DTT was found to inactivate VACV after a 3-h incubation at 37°C. The authors suggested that the lipoprotein envelope present around poxviruses accounted for VACV susceptibility to DTT. 

Vimses are made up of a protein capsule, some with a lipoprotein envelope around it, containing genetic material (either DNA or RNA), with maybe a few enzymes but very little else and hence they are not considered to be cells, but, rather, infectious particles. Viruses are able to bind to cell membranes, penetrate and infect cells of other organisms. Viruses are intracellular parasites they cannot replicate themselves without using the contents of the host cell to synthesize the cellular components necessary for their reproduction. This makes the development of effective antiviral drugs that do not damage healthy host cells very difficult. 

The virion (the complete infective virus, such as exists extracellularly) consists of a core of either DNA or RNA (but not both) surrounded by a protective capsid (= shell) of one, or sometimes two, proteins. These two components are arranged in a highly ordered fashion that is characteristic of the particular kind of virus. Most of the viruses that infect animals are icosahedral (20-sided) and hence roughly spherical. But the viruses of measles and influenza are spirals. In the latter virus two kinds of protein (neuraminidase and haemagglutinin) form the capsid which is embedded in lipid, and this lipoprotein envelope encloses a coiled ribonucleoprotein tube. Poxviruses (which include the herpesviruses) are the largest known, brick-shaped and of very complicated structure. Many types of virus have a protein core around which the nucleic acid is arranged. 

A number of the stages of influenza A and B virus replication are targets for anti-influenza drug development (reviewed in [15,21,22]). A significant amount of research has focused on the functions of the viral surfeice glycoproteins. The surface of the influenza viruses consists of a host-derived lipoprotein envelope in which are embedded an integral ion channel protein and, depending on the virus... 

In general, virus receptors carry out normal functions in the cell. For example, in bacteria some phage receptors are pili or flagella, others are cell-envelope components, and others are transport binding proteins. The receptor for influenza vims is a glycoprotein found on red blood cells and on cells of the mucous membrane of susceptible animals, whereas the receptor site of poliovirus is a lipoprotein. However, many animal and plant viruses do not have specific attachment sites at all and the vims enters passively as a result of phagocytosis or some other endocytotic process. 

Viruses are responsible for a large proportion of the morbidity and mortality experienced worldwide. These infectious agents consist of a core genome of nucleic acid, DNA or RNA (nucleoid) contained in a protein shell (capsid) and sometimes surrounded by a lipoprotein membrane (envelope). Some genera of viruses are known to cause human infections and include the following adeno, pox and herpesviruses ... 

The products of the major histocompatibility locus have been shown to interact with viral antigens on the cell surface of thymocytes. A number of polypeptides bind to the major envelope glycoprotein of Rauscher murine leukaemia virus. The receptors for this glycoprotein, which probably involve lipoproteins, have been prepared from plasma membrane preparations from mouse cells. ... 

Viruses are subcellular and submicroscopic agents of varied shapes that have genes made of a nucleic acid (DNA or RNA) central core. This core is enclosed in a protective protein, and it can also be enveloped in a lipoprotein membrane. Viruses are not considered to be living organisms. 

Tanada (57) reported that the Hawaiian strain of the armyworm, ftewda/et/a unipuncta, granulosis virus (GV) enhanced infectivity of the armyworm NPV when they were fed simultaneously. Since then, a viral lipoprotein in the GV occlusion body was identified as the synergistic factor (SF). Preliminary tests indicated that the SF enhanced infectivity of GVs and NPVs of the armyworm, the cabbage looper (Trichoplusia ni and the beet armyworm (Spodoptera exigua) in their respective hosts (38). Uchima et sd. (59) demonstrated that the SF binds to midgut membranes and may serve as attachment sites for the enveloped virions. 

---