In this regard, even if they have no DNA and RNA, they behave like viruses, producing mutations structural distinct self-perpetuating offering a clear evolutionary advantage.
The study was published this week in rapid review Proceedings of the National Academy of Sciences and online publishing.
"We have discovered that when a strain specific prion is transferred to a different cell line brain cells, its properties change gradually, giving rise to a variant strain which is better suited to this new cell environment," said Charles Weissmann, MD, Dr., head of the Department of infectology Florida Scripps, who led the study. "If these same prions are then transferred to another cell lineage, they change again, to adapt to these new host cells. And if it is returned to the brain, prions gradually regain their original properties. We have found material evidence that, at least in one case, the prion protein fold changed when its modified properties. »
Darwinian evolution without DNA
These new results come about a year after Weissmann and colleagues published a study in the edition of the journal Science which showed that the prions were capable of Darwinian evolution on 1 January 2010.
This study also showed that prion can develop a large number of mutations and mutations can bring such evolutionary adaptations that resistance to medicines, a phenomenon previously known only in bacteria and viruses. This study has also been suggested as normal - prion protein that occurs naturally in the cells of mammals – may prove more effective than its abnormal relationship with toxic therapeutic target.
"Because the prion can adapt to changing environments, it now becomes clear that it will be harder only imagined initially find medicines that will work against them," said Weissmann. "But if you could develop a drug that inhibits the formation of normal prion protein, you could essentially starving infectious prions and prevent reproduction." This approach to treatment, although technically demanding, may be considered because, as we have shown previously, deprivation of PrP is not harmful to health — at least for the health of the mouse. »
Folding and misfolding
Prions, which are composed only of protein, are classified by different strains, characterized by their incubation time and they cause disease. In addition to the BSE mad cow disease in cattle diseases caused by prions include scrapie in sheep, chronic wasting disease in deer and variant Creutzfeldt-Jakob disease in humans. Prions have the ability to reproduce, despite the fact that they contain no genome nucleic acid.
Mammalian cells normally produce cellular prion protein or PrPC. To infection, abnormal or poorly folded - protein called PrPSc - converts protein prion normal host in its toxic form by changing its shape or conformation. The Terminal is composed of large sheets (polymers) of these proteins, which causes mass of tissue and cell damage.
"The protein infectious prion can fold in different ways and according to the fold, results, different prion strain" said Weissmann. "As long as prions are stored in the same host, they retain their fold, feature so that the stem reproduce true."
When prions multiply, however, this trick is not always correctly reproduced, with a population of prions contains many variants, albeit at low levels.
The new study found that when a prion population is transferred to a different host, one of the variants may reproduce faster - an evolutionary advantage - and become the dominant strain. This new population also contains variations, which may be selected on others when transferred to a different host.
"The result is that pray much devoid of genetic material, behave similarly to viruses and other pathogens, they can mutate and undergo an evolutionary selection," said Weissmann. "They do by modifying their folds, while viruses undergo changes in their sequence of nucleic acids".
Various related yet
The new study suggests that prions populations constitute a "quasi-species" similar to RNA viruses and retroviruses, such as influenza viruses and HIV.
The idea of a quasi species was designed by Manfred Eigen, a German biophysicist who won the Nobel Prize in chemistry in 1967. Basically, a species almost is a complex population, self-perpetuating related and diverse entities that act in its entirety. It was Weissmann, however, that, in 1978, provided the first confirmation of the theory through the study of a particular Bacteriophage - a virus that infects bacteria - while he was Director of the Institut für Molekularbiologie Zurich Switzerland.
But this is where the comparison ends, Weissmann said.
"The fact that they behave like viruses does not mean that they are something like a virus", he said. "A bike is like a car that gets you from one location to another, but they are not the same." The end effect is the same, however. Prions, and viruses are able to modify their structure to survive.
The first author of the study is Sukhvir P. Scripps Research Mahal. Among the other authors Shawn Browning, Jiali Li and Irena Suponitsky-Kroyter to Scripps Research.
The study was supported by the National Institutes of Health and family Alafi Foundation.
Warning: this article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those PharmaLive.com or its staff.
Source of the story:
The story above is reproduced (with drafting adaptations by PharmaLive.com staff) of materials supplied by The Scripps Research Institute.
Reference of the review:
S. P. Browning Mahal, s., j. LI, i. Suponitsky Kroyter, c. Weissmann. The transfer of a strain of prions for different hosts led to the emergence of variants of strain. Proceedings of the National Academy of sciences, 2010; DOI: 10.1073/pnas.1013014108Note: If no author is given, the source is cited for this.
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