The protein component of scrapie-associated fibrils is a glycosylated low molecular weight protein.

Abstract

Scrapie‐associated fibril protein (SAF‐protein) extracted from infectious scrapie‐associated fibrils (SAF) isolated from scrapie hamster brains is not infectious. SAF‐protein is composed of various mol. wt. species of glycoproteins differing in carbohydrate content rather than amino acid composition. The N‐linked carbohydrate chains represent approximately 40‐60% of the mol. wt. of SAF‐protein. The deglycosylated SAF‐protein has a surprisingly low mol. wt. of approximately 7 kd, representing approximately 55 amino acid residues. This size and chemical analyses indicate that SAF‐protein is an amyloid‐type of protein. The simplest explanation for the available data is that SAF‐polypeptide is very likely not to be part of the scrapie agent but that it is, like other amyloid proteins, derived from host‐encoded proteins and not infectious. It is suggested that the infectivity of fractions rich in SAF is due to co‐purification of scrapie virus and SAF caused by the high carbohydrate content of SAF‐protein.