Satheeshkumar KS, Murali J, Jayakumar R. Assemblages of prion fragments: novel model systems for understanding amyloid toxicity.
J Struct Biol 2004;
148:176-93. [PMID:
15477098 DOI:
10.1016/j.jsb.2004.05.006]
[Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2004] [Revised: 05/10/2004] [Indexed: 11/21/2022]
Abstract
We report the conformational and toxic properties of two novel fibril-forming prion amyloid sequences, GAVVGGLG (PrP(119-126)) and VVGGLGG (PrP(121-127)). The conformational preferences of these fragments were studied in differing microenvironments of TFE/water mixtures and SDS solution. Interestingly, with an increase in TFE concentration, PrP(119-126) showed a helical conformational propensity, whereas PrP(121-127) adopted a more random coil structure. In 5% SDS, PrP(119-126) showed more alpha-helical content than in TFE solution, and PrP(121-127) exhibited a predominantly random coil conformation. However, both peptides took a random coil conformation in water, and over time the random coil transformed into a beta-sheet structure with a significant percentage of helical conformation and beta-turn structure in PrP(119-126) and PrP(121-127), respectively, as observed with CD spectroscopy. The aged fibrils of PrP(119-126) were insoluble in SDS, and PrP(121-127) was extractable with SDS solution. These fibrils were characterized by transmission electron microscopy. Both PrP(119-126) and PrP(121-127) formed stable monolayer's consisting of multimeric assemblages at the air-water interface. Monomeric PrP(119-126) was more toxic to astrocytes than the control Abeta peptide; however, the fibrillar form of PrP(119-126) was less toxic to astrocytes. PrP(121-127) elicited moderate toxicity in both soluble and fibrillar forms on astrocytes. Furthermore, quenching experiments using acroyl-labeled PrP(119-126) and PrP(121-127) with eosin-labeled synaptosomal membrane revealed that these prion fragments bind to anion-exchange protein. The binding of PrP(119-126) and PrP(121-127) with a membrane microdomain (lipid raft) was also analyzed using pyrenated derivatives. We conclude that the formation of PrP(119-126) and PrP(121-127) fibrils is a concentration-dependent process that involves coil to sheet conversion with aging. PrP(119-126), the sequence with intrinsic helical propensity, is more toxic in monomer form, and the fibril formation in this case seems to be protective to cells. For PrP(121-127), the SDS-soluble fibrils are more cytotoxic, indicating that a higher order assemblage structure is required for cytotoxic activity of this peptide.
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