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 (PrPC), known as PrPres. 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 HD, PrP106-126 A and PrP106-126 K, with L-His → D-His, His → Ala and His → Lys substitutions respectively at position 111, PrP106-126 NH2 with amidation of the C-terminus, PrP106-126 V with an Ala → Val substition at position 117, and PrP106-126 VNH2 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) His111 is central to the conformational changes of PrP peptides. (2) Amidation of the C-terminal Gly126 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 NH2 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.

NMR-detected hydrogen exchange and molecular dynamics simulations provide structural insight into fibril formation of prion protein fragment 106–126

“…Although the MD simulations suggest a preference for parallel orientations, the symmetric sequence motif may allow more heterogeneous structures containing both parallel and antiparallel orientations (depending on other regions of the protein), resulting in increased entropy for amyloid formation. Given the high stability and favorable structural properties of our computational model of the PrP106-126 fibrils, which is fully consistent with all experimental observations reported here (amide protection, CD, and electron microscopy) and with the results of previous biophysical and mutational studies on related peptides (7)(8)(9)(10)(11)29), it appears likely that this unusual sequence motif plays an important role in converting the monomeric PrP C into its neurotoxic and infectious scrapie form.…”

“…5c). Interestingly, replacement of this conserved histidine residue with a D-amino acid (D-His) was found to disrupt fibril formation of the human PrP106-126 peptide (8), confirming the importance of this residue.…”

“…2, E), suggesting an increase in ␣-helix content at the expense of ␤-structure and random coil. The CD spectrum was unaffected by further addition of Ͼ50% (vol͞vol) acetonitrile, indicating that fibril formation had reached a stable plateau (8). Although the rate of fibril formation for MoPrP106-126 appears to be faster than the rate reported for other peptides, such as Alzheimer's disease ␤-peptides (20), an exact comparison would require a more detailed analysis, including studies of the effects of seeding.…”

“…The MoPrP106-126 peptide (TNVKHVA-GAAAAGAVVGGLGG, palindrome underlined) studied here is homologous to residues 107-127 of human PrP (TNMKHMA-GAAAAGAVVGGLGG). The fibril-forming tendencies of PrP106-126 depend critically on the solvent environment (8,9). The conditions chosen for this work [100 mM sodium acetate͞ 150 mM NaCl, pH 5.5͞50% (vol͞vol) acetonitrile] have been shown to facilitate fibril formation in a related prion peptide (9).…”

“…Analysis of deletion mutants of human prion protein (PrP) showed that a large N-terminal fragment (residues 23-88) and a segment within the structured domain of PrP C (residues 141-176) could be deleted without affecting its conversion into the protease-resistant PrP Sc , whereas deletion of segments 95-107, 108-121, or 122-140 abolished the conformational transition (7). PrP106-126 is located within this critical region (residues 95-140), has been shown to adopt different secondary structures under different solution conditions (8,9), and is thus a relevant model for investigating the mechanism of fibril formation and PrP Sc -mediated cell death. Recent solid-state NMR results showed that fibrils of the mouse prion peptide 89-143 are composed predominantly of ␤-structure, and they suggested that its pathogenicity is related to the specific ␤-sheet conformation (10,11).…”