Researchers from the University of North Carolina at Chapel Hill, in the current issue of PLoS Computational Biology, had reported that there may be possible molecular origin of at least nine human diseases of nervous system degeneration.
These neuro degenerative diseases, including Huntington's disease, share an abnormal deposit of proteins inside nerve cells. This deposition of protein results from a kind of genetic stutter within the cell's nucleus asking for multiple copies of the amino acid glutamine, a building block of protein structure. These disorders are collectively known as polyglutamine diseases.
Along with Huntington's, these diseases include spinobulbar muscular atrophy; spinocerebellar ataxia types 1, 2, 3, 6, 7 and 17; and dentatorubral-pallidoluysian atrophy, or Haw River Syndrome.
Scientists are uncertain if protein deposition causes nerve cells to deteriorate and die. However, studies show that the greater the number of glutamine repeats in a protein above a certain threshold, the earlier the onset of disease and the more severe the symptoms.
This result suggests that abnormally long glutamine tracts render their host protein toxic to nerve cells.
In their new study, researchers had sought to determine why a correlation exists between polyglutamine expansion length and nerve cell death, or disease. They hypothesized that expansion of glutamines results in alternative structures forming within the protein that compete with its normal structure and function.
Researchers used computer simulations to mimic polyglutamine behavior. The UNC study showed that when the number of glutamine repeats exceeds a critical value, the glutamines tend to take on a specific shape in the protein called a beta helix. Moreover, the tendency to form a beta helix increases as glutamine tract length becomes longer.