Agent

In 1982 Prusiner first described the concept of the prion to characterize the agent that causes TSEs. Prions are small proteins (253 amino acids in humans) that are encoded on different chromosomes in different species. The exact function of the prion protein is unknown, but it is believed to be involved in neuronal copper metabolism and synaptic transmission. Normal cellular prion protein (PrPc) is susceptible to degradation by protease. However, in certain instances PrPc is converted to a protease resistant form of the protein (PrPres) that accumulates in neural tissue, inevitably resulting in degenerative disorders and death (104-107).

PrPc and PrPres are identical in terms of their primary amino acid sequence and differ only in conformational changes. It is theorized that a post-transla-tional, conformational change of PrP alpha-helices into beta-sheets is the pathologic mechanism causing change from PrPc to PrPres. Following introduction of PrPres into the mammalian body, PrPres promotes conversion of PrPc to PrPres through direct contact, resulting in a toxic accumulation of PrPres in neurologic tissue (102-107).

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