Tetraspanins also known as tetraspans or the transmembrane 4 superfamily (TM4SF) are type III membrane glycoproteins which span the plasma membrane four times found in all multicellular eukaryotes. They consist of four transmembrane domains, intracellular N- and C-termini and two extracellular domains, one short (called the small extracellular domain or loop, SED/SEL or EC1) and one long, usually 100 amino acid residues (the large extracellular domain/loop, LED/LEL or EC2) that is subdivided into a constant region containing various protein-protein interaction sites. An important structural feature of the superfamily is the “tetraspanin fold” of the larger extracellular loop (LEL). Here, disulfide bonding of four absolutely conserved cysteines form a subloop structure encompassing a region which is hypervariable between family members and between species homologues of the same tetraspanin. The cysteines are present in three variously conserved motifs: CysCysGly, ProXSerCys (where X = any amino acid) and GluGlyCys, wherein the flexibility and constraint imparted by the conserved Gly residue in CysCysGly and by Pro in ProXSerCys contribute to subloop formation. The region of the LEL outside of this subloop shows better structural conservation, developing three α-helices which not only form a structural platform to present the tetraspanin fold but may also act as an independent contributer to tetraspanin function. The large extracellular loop (LEL) of tetraspanins has been given most attention because it contains functionally important sites like sequence QRD (194–196) in CD151 that is important for association with integrins and is functionally important for integrin-dependent cell spreading and multicellular cable formation. A pos... ... middle of paper ... ...r SDS. Tetraspanins have been recognized as the targets of antibodies which obstruct the infection of a range of viruses. But, it appears that at least two tetraspanins may be involved in HTLV-1 infection and at least four in HIV-1 infection. Thus, it is postulated that quite a lot of tetraspanins will be involved in some or all of the viral life cycles already known and yet to be discovered. Tetraspanins are also famous for their roles in the pathology of infectious diseases such as diphtheria, malaria, and numerous viral infections. From literature, we know that specific tetraspanin family members are selectively linked with particular viruses and affect several stages of infectivity, from initial cellular attachment to syncytium formation and viral particle release concluding that the relationship of tetraspanins with viruses look like it is particularly complex.
These cells form a shape such that each individual cell always remains in contact with 3 other cells at all times. The cells are held together by regions known as intercalated disks. These overlapping, finger-like extensions of the cell membrane contain gap junctions and desmosomes. Gap junctions are protein-lined tunnels which allow currents to travel from cell to cell to ensure the cells contract in unison. Desmosomes are known to hold the heart cells together during a contraction.
Guyer, Ruth Levy, Ph.D. “Prions: Puzzling Infectious Proteins” National Institutes of Health Office of Science. 28 July 2006 < science.education.nih.gov/nihHTML/ose/snapshots/multimedia/ritn/prions/prions1.html>.
In 1989, Fogleman et al. analyzed the uncoating and penetration of Simian virus (SV 40). It uses the ganglioside...
Cytomegalovirus (CMV) is the most common virus in the United States that can infect almost any individual. Cytomegalovirus is also referred to as Herpesvirus-5, which belongs to a branch of Herpesviridae family. Herpesviridae has a spherical shape that contains four significant elements that are important to the viron. The four elements are the core, tegument, capsid and the envelope. Alphaherpesvirinae, Betaherpesvirinae and Gammaherpesvirinae are three subfamilies which belong to Herpesviridae. Cytomegalovirus belongs to the Betaherpesvirinae family, which also include Muromegalovirus and Roseolovirus. The Alphaherpesvirinae subfamily includes Simplexvirus, Varicellovirus, Mardivirus and Iltovirus genera. The Gammaherpesvirinae subfamily contains Lymphocryptovirus and Rhadinovirus genera. The diameter size of the virus is based on each specific family; however, the core remains the same throughout the species, which contains single layer of double stranded DNA tightly condensed in the capsid. In the tegument component, there are 30 or more viral proteins that are shapeless that encompass the capsid. Out of the four major components, the tegument has the most poorly defined structure. On the other hand, the capsid is a well-defined structure that is an icosahedron, which is composed of 162 capsomeres, 12 of which are pentons and 150 are hexons (1). Last but not least, the liquid envelope surrounds the tegument with approximately 10 glycoprotein and cellular proteins. Each subfamily under the herpesviriade has its own arrangement between the liquid envelop and the tegument layer.
Orthopoxvirus variola is the virus responsible for the well-known smallpox disease. It belongs to the Poxviridae family which is further split into the subfamilies Entomopoxivirinae which only affects insects, and Chordopoxivirinae which infects vertebrae (Hughes). It is in group one of the Baltimore Classification since it possesses double-stranded DNA. This group also includes viruses in the Herpesviridae family, certain bacteriophages, as well as the mimivirus. The linear genome consists of approximately 186 kb pair and, like all orthopoxviruses, is about 200 nm in diameter (Li; Riedel). Virus particles may be enveloped, but the majority will be nonenveloped when released from a lysed cell, ready and capable to affect another. Extracellular enveloped viruses evolve from their precursors intracellular enveloped virus and cell-associated enveloped virus and contain proteins that aid the virus in neutralizing host cell antibodies to enhance virus spread (Smith). Entrance into the host cell may be accomplished by fusion of endocytosis, contingent on the particular strain. Host cell cytoplasm is the site of poxvirus replication, therefore host nuclear enzymes are unavailable to the virus; to overcome this, DNA-dependent RNA polymerase enters the host with the virus (Hughes).
...rticular protein, called MAVS, which is key to our innate ability to fight certain viral infections, acquires a self-perpetuating fibrillar form in cells that have become infected with virus and amplifies the cellular alarm signal. [7] This ultimately induces the production of interferons that recruit macrophages to combat the infection. [7]
3. In the same month in which Gallo's and Essex's groups reported their data, Luc Montagnier and his colleagues from the Pasteur Institute, described the isolation of a retrovirus, later known as Lymphadenopathy Associated Virus (LAV), from the lymph nodes of a homosexual patient with lymphadenopathy.(5) Although this virus was similar to HTLV-I, one of its proteins, a protein with a molecular weight of 24,000 (p24), did not react with monoclonal antibodies to the HTLV-I p24 protein. Samples of this virus were, on several occasions, sent to Gallo's laboratory.
Schulman, Joshua M., and David E. Fisher. "Abstract." National Center for Biotechnology Information. U.S. National Library of Medicine, 28 Aug. 0005. Web. 24 Apr. 2014.
The virus is primarily spherical shaped and roughly 200nm in size, surrounded by a host-cell derived membrane. Its genome is minus-sense single-stranded RNA 16-18 kb in length. It contains matrix protein inside the envelope, hemagglutinin and neuraminidase, fusion protein, nucleocapsid protein, and L and P proteins to form the RNA polymerase. The host-cell receptors on the outside are hemagglutinin and neuraminidase. The virus is allowed to enter the cell when the hemagglutinin/ neuraminidase glycoproteins fuse with the sialic acid on the surface of the host cell, and the capsid enters the cytoplasm. The infected cells express the fusion protein from the virus, and this links the host cells together to create syncitia.
The cause of acquired immune deficiency syndrome (AIDS) is human immunodeficiency virus type 1 (HIV-1). HIV-1 is not just one virus, but comprises four distinct lineages each with very different frequency and each resulting from an independent cross-species transmission event. The groups are named M, N, O, and P; M is the most widespread form and constitutes about 98% of HIV infection around the globe (Sharpe 2010 2487). Groups N, O, and P are rare, and largely restricted to Cameroon and surrounding countries. The forth and most recent P group strain of HIV-1 is closely related to the gorilla viruses and has most likely resulted from gorilla-to-human transmission (Sharp & Hahn 2489). The HIV virus blocks the functions of tetherin in the human body. Tetheirn is a mammalian host protein with a recently discovered antiviral activity. Tetherin dimers appear to form ‘tethers’ between virus envelopes and the cytoplasmic membrane of the cell, preventing the release of those viruses. HIV-1 has adapted over time in attempts to counteract tetherin, which has yielded different results and caused the formation of M, N, O, and P. Only in the case of HIV-1 group has adap...
conducted a study in hopes of revealing more information about the unknown mechanism linking SOD1 mutations to FALS. To do this, they conducted structural, biochemical, and biophysical characterizations of two FALS mutant SOD proteins. The study revealed that point mutations lead to destabilization in the protein architecture, which results in the formation of aggregates. Free cysteine residues worsen aggregation because they form disulfide bonds that lock the aggregates in place. Ultimately, the results provide the following mechanism: framework and dimer destabilization lead to the formation of aggregates, which then cause damage to mitochondria and motor neurons. A study conducted by Furukawa et al. provides results that are in agreement with this mechanism. Furukawa et al. tested a FALS mice model in which incorrect disulfide bonds led to the formation of SOD1 aggregates. They found significant amounts of disulfide cross-linked SOD1 aggregates in the spinal cord of symptomatic mice, while no such aggregates were found in non-symptomatic and control
"The Species of the Secondary Protein Structure. Virtual Chembook - Elmhurst College. Retrieved July 25, 2008, from http://www.cd http://www.elmhurst.edu/chm/vchembook/566secprotein.html Silk Road Foundation. n.d. - n.d. - n.d.
The cytoskeleton is a highly dynamic intracellular platform constituted by a three-dimensional network of proteins responsible for key cellular roles as structure and shape, cell growth and development, and offering to the cell with "motility" that being the ability of the entire cell to move and for material to be moved within the cell in a regulated fashion (vesicle trafficking)’, (intechopen 2017). The cytoskeleton is made of microtubules, filaments, and fibres - they give the cytoplasm physical support. Michael Kent, (2000) describes the cytoskeleton as the ‘internal framework’, this is because it shapes the cell and provides support to cellular extensions – such as microvilli. In some cells it is used in intracellular transport. Since the shape of the cell is constantly changing, the microtubules will also change, they will readjust and reassemble to fit the needs of the cell.
The lipid bilayer is made up of two layers of amphophilic molecules and their main purpose is to act as a barrier for the cell against water molecules. The two layers are composed of a hydrophilic head and hydrophobic tail and they can form spontaneously. The hydrophilic heads are polar an...
If we examine the detailed structures of many transmembrane proteins, we see that they often have three different domains, two hydrophilic and one hydrophobic .(fig 1&2) A hydrophilic domain (consisting of hydrophilic amino acids) at the N-terminus pokes out in the extracellular medium, a hydrophobic domain in the middle of the amino acid chain, often only 20-30 amino acids long, is threaded through the plasma membrane, and a hydrophilic domain at the C-terminus protrudes into the cytoplasm. The transmembrane domain, because it is made of amino acids having hydrophobic side chains, exists comfortably in the hydrophobic inner layers of the plasma membrane. Because these transmembrane domains anchor many proteins in the lipid bilayer, these proteins are not free-floating and cannot be isolated and purified biochemically without first dissolving away the lipid bilayer with detergents. (Indeed, much of the washing we do in our lives is necessitated by the need to solubilize proteins that are embedded in lipid membranes using detergents!)