[snewk]

Yes, misfolded prion proteins(PrPsc) can 'infect' other correctly folded prion proteins(PrPc). Prions are glycoproteins found on the surface of cells, and they affect cell signaling from the exterior of a cell to the interior.

Insulin, on the other hand, is a free floating small molecule not anchored to a cell. Misfolded insulin is not 'infectious' like PrPsc.

The biological role of prions is still not well known, but one reason prion diseases are such a big deal is that prions are resistant to normal biological protein degredation. They are hard buggers to get rid of. Unlike insulin, which has a specific protease enzyme which breaks it down.