Sludge Watch ==> Prion Propagates in Foreign Host

[Maureen Reilly]

  ScienceDaily

Source: University of Illinois at Chicago
Date: July 6, 2007
More on: Prions, Urology, Gynecology, Microbes and More, Fungus, Cell 
Biology

Prion Propagates In Foreign Host

Science Daily — Using baker's yeast and another fungus, researchers report 
the first successful propagation of a prion from one organism to another.


Prions -- infectious, oddly-folded proteins that are the main suspects in 
fatal neurodegenerative diseases such as Cruetzfeldt-Jakob and bovine 
spongiform encephalopathy, or "mad cow" -- remain mostly a mystery to 
scientists. Very few prions have been fully described. How they infect and 
propagate is not fully understood.

New insights into prion propagation reported in the July 6 issue of 
Molecular Cell by Susan Liebman, university professor of biological sciences 
at the University of Illinois at Chicago, may help tug back the veil on the 
behavior and variety of these potentially lethal molecules.

The work was done with former UIC post-doctoral fellow Vibha Taneja and 
University of Bordeaux researchers Sven Saupe, Marie-Lise Maddelein and 
Nicholas Talarek.

Previously, Liebman focused her studies on prion-forming proteins found in 
baker's yeast, while Saupe's research looked at prion protein in another 
fungus.

A key difference between the two is that the yeast prion proteins are rich 
in the amino acids glutamine and asparagine in the regions of the protein 
used to transform them into a prion. In contrast, the fungal prion lacks a 
rich supply of these amino acids -- a characteristic it shares with the 
prion-forming protein in mammals, which is otherwise dissimilar.

The researchers showed, by fusing the prion-forming domain of the fungal 
protein to a reporter protein, that the fungal prion could propagate in 
yeast.

"We showed that the fusion formed a prion in yeast and it was infectious," 
Liebman said. "It's the first time a prion from one organism has been 
propagated in another organism that normally lacks that prion. It 
demonstrates that totally heterologous prion propagation is possible.

"Surprisingly, the presence of a glutamine and asparagine-rich yeast prion 
that helps other yeast prions to form also helped this one to form," Liebman 
said, showing that prions of one type can interact with a dissimilar type.

Liebman said the finding suggests the possibility that yeast itself may 
contain non-glutamine and asparagine-rich prions. "We just haven't looked 
for them," she said.

The finding also underscores the value of the yeast model for studying 
factors necessary to propagate prions, now that it's been shown that 
propagation is not necessarily host-specific.

Liebman said the research emphasizes the need to look for new prions.

"How many more are there? Are there lots that we haven't looked at? How do 
we look for them? These are open questions."

Note: This story has been adapted from a news release issued by University 
of Illinois at Chicago.