The PrP-like proteins Shadoo and Doppel.

An almost unique place within protein databases, twenty-five years of study has underscored the enigmatically subtle role of PrP(C) in normal cell biology. It seems that PrP has evolved (and survived) to perform a function that does not have a precedent amongst transmembrane cell-surface proteins, perhaps representing a new type of plasma membrane ecosystem. In a context where we await a clarifying insight to unify a panoply of PrP(C) data into logical molecular framework, the GPI-anchored N-glycosylated Doppel and Sho proteins are tantalizing in that they correspond roughly to the front and back halves of PrP(C) itself. These molecules may be simpler - and more "understandable" - entities that can be pursued in parallel to PrP(C), and could open up the biology of mammalian prion proteins from fresh directions. Dpl has a profound role in successful gametogenesis that warrants close scrutiny and a case for deeper study can be made for Sho, a recently discovered CNS-expressed protein with many parallels to established facets of PrP biochemistry. In an aerial view of biomedical research, Sho and Dpl can be considered as adjacent islands in a prion protein archipelago. As such, the coming years of molecular exploration should be extremely interesting.