Annular α-Synuclein Protofibrils Are Produced When Spherical Protofibrils Are Incubated in Solution or Bound to Brain-Derived Membranes

Abstract

The Parkinson's disease substantia nigra is characterized by the loss of dopaminergic neurons and the presence of cytoplasmic fibrillar Lewy bodies in surviving neurons. The major fibrillar protein of Lewy bodies is alpha-synuclein. Two point mutations in the alpha-synuclein gene are associated with autosomal-dominant Parkinson's disease (FPD). Studies of the in vitro fibrillization behavior of the mutant proteins suggest that fibril precursors, or alpha-synuclein protofibrils, rather than the fibrils, may be pathogenic. Atomic force microscopy (AFM) revealed two distinct forms of protofibrillar alpha-synuclein: rapidly formed spherical protofibrils and annular protofibrils, which were produced on prolonged incubation of spheres. The spherical protofibrils bound to brain-derived membrane fractions much more tightly than did monomeric or fibrillar alpha-synuclein, and membrane-associated annular protofibrils were observed. The structural features of alpha-synuclein annular protofibrils are reminiscent of bacterial pore-forming toxins and are consistent with their porelike activity in vitro. Thus, abnormal membrane permeabilization may be a pathogenic mechanism in PD.

Are amyloid diseases caused by protein aggregates that mimic bacterial pore-forming toxins?

“…Amyloid fibril formation by a-synuclein occurs by a hierarchical assembly mechanism (random coilpspherespchain-like and annular protofibrilspfibrils) similar to that observed for Ab in AD Ding et al 2002). The PD-linked mutations promote formation of annular and tubular protofibrillar structures (wild-type a-synuclein forms annular protofibrils after extended incubation) Ding et al 2002 ;Lashuel et al 2002a, b) (Fig. 2b, d ).…”

“…Any model for pathogenesis must explain these cases. It is important to emphasize that the wild-type proteins will also form amyloid pores in vitro, albeit more reluctantly than the disease-associated mutants (Hafner et al 2001;Ding et al 2002 ;Lashuel et al 2002aLashuel et al , b, 2003Shtilerman et al 2002 ;Chromy et al 2003 ;Chung, 2003 ;Klug et al 2003 ;. Factors other than mutations could trigger pore formation pathogenesis in sporadic disease (Fig.…”

Lewy bodies

“…Lansbury and coworkers (132)(133)(134) have extensively evaluated the possibility that ␣-SYN fibrils may not be toxic; rather, intermediates, which they have termed protofibrils, may be the toxic compounds. The protofibrils, which, like ␣-SYN fibrils, contain ␤-sheet structures, occur early in the fibrillation process.…”

“…The protofibrils, which, like ␣-SYN fibrils, contain ␤-sheet structures, occur early in the fibrillation process. Atomic force microscopic images at steps in the fibrillation process indicated that ␣-SYN first formed spherical protofibrils, which progressed to chain and annular protofibrils, and some or all of these were converted to fibrils (133). In cultured cells, overexpression ␣-SYN or treatment with a mitochondrial inhibitor resulted in two distinct forms of aggregated ␣-SYN; small spheres of ␣-SYN, which formed first; and larger inclusions of ␣-SYN (135,136).…”

Orthogonal Cross-Seeding: An Approach To Explore Protein Aggregates In Living Cells

“…alternate aggregation routes or multistep assembly pathway(s), leading to multiple metastable intermediates (14)(15)(16)(17)(18)(19)(20). Current models propose that the species formed early in the course of aggregation, e.g., oligomers and protofibrils, are likely culprits in cytotoxicity and cell dystrophy (21)(22)(23)(24)(25).…”