Major prion protein (PrP, for prion protein or protease-resistant protein), also known as CD230 (cluster of differentiation 230), is the only known example of a prion protein in animals. In humans, it is encoded by the PRNP gene (PRioN Protein). Expression of the protein is most predominant in the nervous system but occurs in many other tissues throughout the body.The protein can exist in multiple isoforms, the normal PrPC, the disease-causing PrPSc, and an isoform located in mitochondria.