Prions
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Monday, October 11, 2010
Canned Foods And Metallic
E 'has been established for years that the head of the so-called "mad cow disease
" of scrapie in sheep and
' s
' s
bovine spongiform encephalopathy
(Alzheimer's
(Alzheimer's
disease and kuru-creuzfeltdt jaocob ) in man is nothing but a small protein known as a prion. The 
prions are nothing but small
glycoproteins localized 
prions are nothing but small boobies cell membranes of the system nervous. Why cause a disease such as mad? Prions are proteins that can take two different forms, one regular and one wrong. For the truth is known that many proteins are flexible assume different conformations, prions, however, have a special feature: if assumonouna the wrong shape can cause normal prions to take the form incorrect. In this way a small number of abnormal prions can ruin an entire population of normal prions convert one by one in the wrong format. This can have very serious consequences as they increase in body levels of prion protein transformed.
For example, the incorrect folding of the prion PrP The normal form of prion protein PrP
, shown here, is on the surface of nerve cells, but when it takes the form incorrect, the aggregates into long fibrils that block the normal functioning of the brain. Infection occurs when a small amount of protein from the erroneous form enters the body because it is eaten or through a wound. A dramatic case of this kind occurred between the native population of the island of Papua New Guinea because of the rites of cannibalism that accompanied the funeral ceremonies. The outbreak probably began when a person has developed the disease spontaneously, in fact, the susceptibility to diseases caused by abnormal prions can be hereditary, and it is possible involvement of DNA or RNA, it seems that in all mammals there are genes for the predisposition to form abnormal protein that then allows the transmission of the disease but, but even if many individuals with genetic predisposition do not develop any type of prion disease unless they come into contact with abnormal forms of the protein. The abnormal prions have spread throughout the community when the infected person has been eaten. More recently there has been widespread concern that the prions that cause cattle in the mad cow disease may be transmitted to humans by eating infected meat. The bovine PrP protein is in fact very similar to that in humans and are seen many cases of this type of infection.
prion protein PrP 
. The large domain on the left image above was obtained from the PDB file
1qm2 
. It has a lipid attached to the bottom that serves to anchor the protein to the surface of nerve cells and also has two carbohydrate chains.
. It has a lipid attached to the bottom that serves to anchor the protein to the surface of nerve cells and also has two carbohydrate chains. The remainder of the protein chain is very flexible and her two portions were studied by NMR spectroscopy getting the PDB file 1oei and 1skh . Although the prion PrP have been studied for years, much remains to be understood. We know that there are nerve cells, but their exact function has not yet been determined with certainty. In addition, researchers have not yet discovered the structure of the form wrong and infectious prion PrP. The structure shown below, however, can give us an idea of \u200b\u200bhow it could be.
Prions functional. Nature is full of surprises and prions are no exception. While humans and other mammals, prions can cause a terrible disease, other organizations use to stay healthy prions. Some fungi, for example, synthesize the HET-s prion protein, shown here in its incorrect form, from the PDB file 2rnm. This protein has a particular role in the growth of fungi. Some individuals have a variety of HET-s that can take only one form, while other individuals have a variety of slightly different protein that can take both forms. When two colonies of fungi are in contact with each other, exchange some biological material by fusing cells, forming some large cells with multiple nuclei. The fused cells die if they have incompatible forms of HET-s protein. This becomes an advantage because it promotes the biological diversity in the population, while maintaining the separate colonies and then limiting the spread of viral infections.
When you take the wrong form, prions aggregate to form fibrils very compact and can not be degraded by cellular proteolytic enzymes. We can get an idea of \u200b\u200bthe structure of these fibrils by examining the figure at right 2rnm obtained from the PDB file, which includes part of the prion protein HET-s of fungus. This file includes a short fibril consists of ten different protein chains stacked to form a solenoid structure. Some non-polar amino acids, highlighted in white, (valine, leucine and isoleucine) are addressed within this solenoid and, by binding together by hydrophobic bonds, help to stabilize the structure in this conformation. The protein chains that make up the fibril, have assumed a form which we have hitherto called "wrong". Were transformed from normal structure to alpha-helix in beta sheets folded
highlighted in yellow in the two figures below (these are also taken from the PDB file 2rnm). The folded beta sheet structure has the characteristic of being "sticky" because they form hydrogen bonds with another folded beta-chain with which they approached the side.
Nearly all proteins have some features in which beta-folded structures can sometimes generate specific within the protein such as the walls of a cylindrical shape in which small molecules can be accommodated. 
In some cases, however, the stickiness of these side chains may promote abnormal aggregation of a protein with the other, as shown at right. Are created, thus, the large aggregates consisting of many proteins that form of stacked long amyloid fibrils calls for taking microscopic appearance similar to grains of starch plant tissue.
Sources: pdb
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