Molecular determinants of the physicochemical properties of a critical prion protein region comprising residues 106–126

Abstract

Prion diseases are marked by the cerebral accumulation of conformationally modified forms of the cellular prion protein (PrP(C)), known as PrP(res). The region comprising the residues 106-126 of human PrP seems to have a key role in this conformational conversion, because a synthetic peptide homologous with this sequence (PrP106-126) adopts different secondary structures in different environments. To investigate the molecular determinants of the physicochemical characteristics of PrP106-126, we synthesized a series of analogues including PrP106-126 H(D), PrP106-126 A and PrP106-126 K, with l-His-->d-His, His-->Ala and His-->Lys substitutions respectively at position 111, PrP106-126 NH(2) with amidation of the C-terminus, PrP106-126 V with an Ala-->Val substition at position 117, and PrP106-126 VNH(2) with an Ala-->Val substitution at position 117 and amidation of the C-terminus. The analysis of the secondary structure and aggregation properties of PrP106-126 and its analogues showed the following. (1) His(111) is central to the conformational changes of PrP peptides. (2) Amidation of the C-terminal Gly(126) yields a predominantly random coil structure, abolishes the molecular polymorphism and decreases the propensity of PrP106-126 to generate amyloid fibrils. (3) PrP106-126 V, carrying an Ala-->Val substitution at position 117, does not demonstrate a fibrillogenic ability superior to that of PrP106-126. However, the presence of Val at position 117 increases the aggregation properties of the amidated peptide. (4) Amyloid fibrils are not required for neurotoxicity because the effects of PrP106-126 NH(2) on primary neuronal cultures were similar to those of the wild-type sequence. Conversely, astroglial proliferation is related to the presence of amyloid fibrils, suggesting that astrogliosis in prion encephalopathies without amyloid deposits is a mediated effect rather than a direct effect of disease-specific PrP isoforms.