The 673 - kilodalton protease complex consists of 14 copies of two different subunits, alpha and beta, forming a barrel - shaped structure of four stacked rings.
In fatal familial insomnia (FFI), the protease - resistant fragment of PrPSc after deglycosylation has a size of 19 kilodaltons, whereas that from other inherited and sporadic prion diseases is 21 kilodaltons.