title: Gel formation in protein amyloid aggregation: a physical mechanism for cytotoxicity.
abstract: Amyloid fibers are associated with disease but have little chemical reactivity. We investigated the formation and structure of amyloids to identify potential mechanisms for their pathogenic effects. We incubated lysozyme 20 mg/ml at 55C and pH 2.5 in a glycine-HCl buffer and prepared slides on mica substrates for examination by atomic force microscopy. Structures observed early in the aggregation process included monomers, small colloidal aggregates, and amyloid fibers. Amyloid fibers were observed to further self-assemble by two mechanisms. Two or more fibers may merge together laterally to form a single fiber bundle, usually in the form of a helix. Alternatively, fibers may become bound at points where they cross, ultimately forming an apparently irreversible macromolecular network. As the fibers assemble into a continuous network, the colloidal suspension undergoes a transition from a Newtonian fluid into a viscoelastic gel. Addition of salt did not affect fiber formation but inhibits transition of fibers from linear to helical conformation, and accelerates gel formation. Based on our observations, we considered the effects of gel formation on biological transport. Analysis of network geometry indicates that amyloid gels will have negligible effects on diffusion of small molecules, but they prevent movement of colloidal-sized structures. Consequently gel formation within neurons could completely block movement of transport vesicles in neuronal processes. Forced convection of extracellular fluid is essential for the transport of nutrients and metabolic wastes in the brain. Amyloid gel in the extracellular space can essentially halt this convection because of its low permeability. These effects may provide a physical mechanism for the cytotoxicity of chemically inactive amyloid fibers in neurodegenerative disease.
authors.affiliation: InnoMedic Health Applications, Inc., Kennedy Space Center, Florida, United States of America.
authors.forename: Daniel
authors.initials: D
authors.lastname: Woodard
authors.affiliation: Department of Physics and Space Sciences, Florida Institute of Technology, Melbourne, Florida, United States of America.
authors.forename: Dylan
authors.initials: D
authors.lastname: Bell
authors.affiliation: Aerospace Medicine and Occupational Health Branch, Kennedy Space Center, Florida, United States of America.
authors.forename: David
authors.initials: D
authors.lastname: Tipton
authors.affiliation: Department of Physics and Space Sciences, Florida Institute of Technology, Melbourne, Florida, United States of America.
authors.forename: Samuel
authors.initials: S
authors.lastname: Durrance
authors.forename: Lisa Cole
authors.initials: LC
authors.lastname: Burnett
authors.affiliation: Institute of Human Nutrition, Columbia University, New York, New York, United States of America.
authors.forename: Lisa
authors.initials: L
authors.lastname: Cole
authors.affiliation: Biological Sciences Department, Florida Institute of Technology, Melbourne, Florida, United States of America.
authors.forename: Bin
authors.initials: B
authors.lastname: Li
authors.affiliation: Biological Sciences Department, Florida Institute of Technology, Melbourne, Florida, United States of America.
authors.forename: Shaohua
authors.initials: S
authors.lastname: Xu
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D058227:Amyloidogenic Proteins / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D003102:Colloids; D005782:Gels; D018625:Microscopy, Atomic Force; D046529:Microscopy, Electron, Transmission; D009113:Muramidase / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D066263:Protein Aggregation, Pathological; D017433:Protein Structure, Secondary / Q000187:drug effects; D012965:Sodium Chloride / Q000737:chemistry / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000682:Amyloid; D058227:Amyloidogenic Proteins; D003102:Colloids; D005782:Gels; D012965:Sodium Chloride; C421864:hen egg lysozyme; D009113:Muramidase
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