[37] Stable isotope-labeled peptides in study of protein aggregation

This chapter is inspired by studies carried out over several years on synthetic peptides aimed at elucidating aspects of the behavior of the prion protein (PrP) that causes fatal neurodegenerative diseases, often referred to as prion diseases or the transmissible spongiform encephalopathies.

Abstract

This chapter is inspired by studies carried out over several years on synthetic peptides aimed at elucidating aspects of the behavior of the prion protein (PrP) that causes fatal neurodegenerative diseases, often referred to as prion diseases or the transmissible spongiform encephalopathies. These diseases are unique in that they can arise in sporadic, familial, and infectious forms, and the infectious agent is a modified form of a normal cellular protein. Such studies were necessitated by the difficulty of isolating and purifying sufficient PrP from natural sources and difficulties encountered in developing an effective expression and purification system for recombinant PrP to determine three-dimensional structures. Furthermore, it was anticipated that dissection of the entire sequence into shorter fragments might allow a detailed analysis of the structural characteristics of regions of PrP most likely to be involved in its different functions, including its pathogenic behavior. PrP occurs as two physically and biologically distinct isoforms: the normal cellular form, PrPc, and the protease-resistant infectious isoform, PrPSc, which accumulates in amyloid plaques. An N-terminally truncated version of PrPSc (PrP 27-30) was first isolated from scrapie-infected hamster brain, N-terminally sequenced, and cloned. Subsequently, both isoforms of the full-length protein were purified, and although they are dramatically different in their physical properties, they were found to have the same N-terminal sequence. Later studies showed that both isoforms have identical amino acid sequences and chemical posttranslational modifications.