Wang F, Wang X, Yuan CG, Ma J.
Generating a prion with bacterially expressed recombinant prion protein.
Science. 2010 Feb 26;327(5969):1132-5.
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In this paper, Wang et al. report on how they were able to manufacture, with short incubation times, prions capable of infecting wild-type mice. This is an important finding. Looking at the prion field, and the body of research produced over the years, the major efforts were focused on using recombinant proteins to produce infective prions. In our 2004 paper (Legname et al., 2004), we demonstrated that it was possible to create low levels of infectivity using only recombinant prion protein produced in Escherichia coli. After that, there was a major push in research to find out how to enhance these low levels. The main advance came from Surachai Supattapone, formerly of Stanley Prusiner’s lab, when he employed RNA molecules to enhance the production of PrPSc in vitro. Around the same time, Claudio Soto’s group perfected protein misfolding cyclic amplification (PMCA), another important contribution. From then on it was clear that cofactors were probably needed to enhance PrP conversion, and that is basically what the group of Jiyan Ma has just described in their Science paper. They used lipids and RNA, combined with PMCA, to produce highly infectious samples.
This is an important piece of work because it once again confirms that PrP is definitely necessary to create prions, and, perhaps most importantly, it shows that it is actually possible to induce high infectivity with the addition of other cofactors, which are still not well defined but nevertheless necessary to increase the infectivity in the samples. As a matter of fact, these prions are very similar to the mouse-adapted scrapie prions that we already know about, such as the Rocky Mountain Laboratory (RML) strain and others. But the neuropathology that they show is clearly different from RML and any other mouse-adapted prions. All these wild-type prions in mice rarely lead to widespread vacuolation, but the authors here do see vacuolation in many different areas of the brain. A contamination with RML would not explain this.
One puzzling piece of information that is presented in the work of Ma and coworkers is the delayed incubation time upon second passage of these novel prions to the same wild-type recipient mice. Usually, subsequent passages lead to abbreviated incubation times.
In addition, it would be interesting to receive additional information about the stability of their novel prion strain, and more biochemical characterization beyond proteinase K (PK) digestion. One of the things we did with our synthetic prions was to show that they were a completely new set of prions, because they possessed higher stability in terms of resistance to chemical or chaotropic agent denaturation. We found that with synthetic prions, in addition to the neuropathology and to all the other major indications that this is a different prion, the biochemical stability is completely different from any wild-type prion. The authors here did not provide stability data, unfortunately, because it would have given additional indication that they are actually handling something completely different. In our recent work, we also showed how incubation times vary based on the conformation and stability of different synthetic prions (Legname et al., 2006; Colby et al., 2009).
One suggestion of Ma and coworkers’ paper is that whenever you have PK resistance, you have prions, but that’s not always true, because some prions are sensitive to PK attack (Colby et al., 2010).
Legname G, Baskakov IV, Nguyen HO, Riesner D, Cohen FE, Dearmond SJ, Prusiner SB.
Synthetic mammalian prions.
Science. 2004 Jul 30;305(5684):673-6.
Legname G, Nguyen HO, Peretz D, Cohen FE, Dearmond SJ, Prusiner SB.
Continuum of prion protein structures enciphers a multitude of prion isolate-specified phenotypes.
Proc Natl Acad Sci U S A. 2006 Dec 12;103(50):19105-10.
Colby DW, Giles K, Legname G, Wille H, Baskakov IV, DeArmond SJ, Prusiner SB.
Design and construction of diverse mammalian prion strains.
Proc Natl Acad Sci U S A. 2009 Dec 1;106(48) Epub 2009 Nov 13
Colby DW, Wain R, Baskakov IV, Legname G, Palmer CG, Nguyen HO, Lemus A, Cohen FE, Dearmond SJ, Prusiner SB.
Protease-sensitive synthetic prions.
PLoS Pathog. 2010 Jan;6(1):e1000736.