Dataset Information

The protofilament structure of insulin amyloid fibrils.

ABSTRACT: Under solution conditions where the native state is destabilized, the largely helical polypeptide hormone insulin readily aggregates to form amyloid fibrils with a characteristic cross-beta structure. However, there is a lack of information relating the 4.8 A beta-strand repeat to the higher order assembly of amyloid fibrils. We have used cryo-electron microscopy (EM), combining single particle analysis and helical reconstruction, to characterize these fibrils and to study the three-dimensional (3D) arrangement of their component protofilaments. Low-resolution 3D structures of fibrils containing 2, 4, and 6 protofilaments reveal a characteristic, compact shape of the insulin protofilament. Considerations of protofilament packing indicate that the cross-beta ribbon is composed of relatively flat beta-sheets rather than being the highly twisted, beta-coil structure previously suggested by analysis of globular protein folds. Comparison of the various fibril structures suggests that very small, local changes in beta-sheet twist are important in establishing the long-range coiling of the protofilaments into fibrils of diverse morphology.

SUBMITTER: Jimenez JL

PROVIDER: S-EPMC123117 | biostudies-literature | 2002 Jul

REPOSITORIES: biostudies-literature

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The protofilament structure of insulin amyloid fibrils.

Jiménez José L JL Nettleton Ewan J EJ Bouchard Mario M Robinson Carol V CV Dobson Christopher M CM Saibil Helen R HR

Proceedings of the National Academy of Sciences of the United States of America 20020701 14

Under solution conditions where the native state is destabilized, the largely helical polypeptide hormone insulin readily aggregates to form amyloid fibrils with a characteristic cross-beta structure. However, there is a lack of information relating the 4.8 A beta-strand repeat to the higher order assembly of amyloid fibrils. We have used cryo-electron microscopy (EM), combining single particle analysis and helical reconstruction, to characterize these fibrils and to study the three-dimensional ...[more]

PMID: 12093917

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Project description:Detailed structural studies of amyloid fibrils can elucidate the way in which their constituent polypeptides are folded and self-assemble, and exert their neurotoxic effects in Alzheimer's disease (AD). We have previously reported that when aqueous solutions of the N-terminal hydrophilic peptides of AD beta-amyloid (A beta) are gradually dried in a 2-Tesla magnetic field, they form highly oriented fibrils that are well suited to x-ray fiber diffraction. The longer, more physiologically relevant sequences such as A beta(1-40) have not been amenable to such analysis, owing to their strong propensity to polymerize and aggregate before orientation is achieved. In seeking an efficient and inexpensive method for rapid screening of conditions that could lead to improved orientation of fibrils assembled from the longer peptides, we report here that the birefringence of a small drop of peptide solution can supply information related to the cooperative packing of amyloid fibers and their capacity for magnetic orientation. The samples were examined by electron microscopy (negative and positive staining) and x-ray diffraction. Negative staining showed a mixture of straight and twisted fibers. The average width of both types was approximately 70 A, and the helical pitch of the latter was approximately 460 A. Cross sections of plastic-embedded samples showed a approximately 60-A-wide tubular structure. X-ray diffraction from these samples indicated a cross-beta fiber pattern, characterized by a strong meridional reflection at 4.74 A and a broad equatorial reflection at 8.9 A. Modeling studies suggested that tilted arrays of beta-strands constitute tubular, 30-A-diameter protofilaments, and that three to five of these protofilaments constitute the A beta fiber. This type of structure--a multimeric array of protofilaments organized as a tubular fibril--resembles that formed by the shorter A beta fragments (e.g., A beta(6-25), A beta(11-25), A beta(1-28)), suggesting a common structural motif in AD amyloid fibril organization.

Dataset Information

The protofilament structure of insulin amyloid fibrils.

Publications

The protofilament structure of insulin amyloid fibrils.

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