I agree with your comment with alpha-synuclein and its spread. Many many many literature on the topic despite the recent controversial paper on graft and Parkinson´s disease.

http://www.cell.com/cell-reports/pdf/S2211-1247%2814%2900419-7.pdf

I remember many example in which authors speak of "prion-like protein" which sounds correct to me, but this is only my opinion.

As one who participated in the original research efforts to determine prion structure and behavior 30 years ago, I think that Stan's definition of a "proteinaceous infectious particle" is generic, and therefore that it applies to any entity that can perpetuate itself ( meaning its distinct structure). This includes the products of the PRNP gene, Abeta, alpha-synuclein, curli, Sup35, et al. I'm not really sure this question even is at issue in the community.

Thanks for your answer David! There's actually some dispute- various groups have until recently insisted on calling non-prp prion "prionoids" or "prion-like". Classing them as true prions might be misleading- for example, is abeta truly infectious? Have we seen considerable spread to any non-transgenic animal? Contentious debate

Thank you for your explanation. I understand better now. What you are discussing is less a matter of pure science and more a matter of what is called the Sociology of Scientific Knowledge (SSK, for short). SSK depends not only on scientific facts (e.g., "is Abeta infectious?"---and how does one define "infectious?"---but also on epistemic standards that are determined by the relevant scientific community. My earlier answer to the question considered only terminology and how the term "prion" was defined originally. Wittgenstein argued, in essence, that "the meaning of a word hinges on its usefulness in context, not its ideal referent outside of all possible contexts." When we refer to a physical entity as a "prionoid," "prion-like," or simply "prion," we must consider context, and context is one of the matters that you mention in your response above and that is critical in the evaluation of the entire question of "prions." Again, invoking Wittgenstein, "Words and chess pieces are analogous; knowing how to use a word is like knowing how to move a chess piece. Now how do the rules enter into playing the game? What is the difference between playing the game and aimlessly moving the pieces? I do not deny there is a difference, but I want to say that knowing how a piece is to be used is not a particular state of mind which goes on while the game goes on. The meaning of a word is to be defined by the rules for its use, not by the feeling that attaches to the words." ---Wittgenstein, Ludwig and Alice Ambrose (Editor). Wittgenstein's Lectures, Cambridge 1932-1935. Prometheus Books. March 2001. Paperback, 225 pages, Language English, ISBN: 1573928755.

Bottom line: We CAN define our terms, but it is less likely that we can, or even should, seek a static definition for a dynamic entity.

Hmm, interesting! Thank you

This is a very interesting point, trying to find a name for a new entity or group of entities. Certainly after proving with approximative terms ("prion-like", "prionoid") with quite a vague definition, new experimental evidence is driving the concept to the original term, prion. That's the way in which S. Prusiner himself employs it now (Annu Rev Genet. 2013;47:601-23).

A very recent article was written on this very thing! They push for the term propagon in lieu of prion-like.