title: Abeta protofibrils possess a stable core structure resistant to hydrogen exchange.
abstract: Protofibrils are transient structures observed during in vitro formation of mature amyloid fibrils and have been implicated as the toxic species responsible for cell dysfunction and neuronal loss in Alzheimer's disease (AD) and other protein aggregation diseases. To better understand the roles of protofibrils in amyloid assembly and Alzheimer's disease, we characterized secondary structural features of these heterogeneous and metastable assembly intermediates. We chromatographically isolated different size populations of protofibrils from amyloid assembly reactions of Abeta(1-40), both wild type and the Arctic variant associated with early onset familial AD, and exposed them to hydrogen-deuterium exchange analysis monitored by mass spectrometry (HX-MS). We show that HX-MS can distinguish among unstructured monomer, protofibrils, and fibrils by their different protection patterns. We find that about 40% of the backbone amide hydrogens of Abeta protofibrils are highly resistant to exchange with deuterium even after 2 days of incubation in aqueous deuterated buffer, implying a very stable, presumably H-bonded, core structure. This is in contrast to mature amyloid fibrils, whose equally stable structure protects about 60% of the backbone amide hydrogens over the same time frame. We also find a surprising degree of specificity in amyloid assembly, in that wild type Abeta is preferentially excluded from both protofibrils and fibrils grown from an equimolar mixture of wild type and Arctic mutant peptides. These and other data are interpreted and discussed in terms of the role of protofibrils in fibril assembly and in disease.
authors.affiliation: Graduate School of Medicine, University of Tennessee, 1924 Alcoa Highway, Knoxville, Tennessee 37920, USA.
authors.forename: Indu
authors.initials: I
authors.lastname: Kheterpal
authors.forename: Hilal A
authors.initials: HA
authors.lastname: Lashuel
authors.forename: Dean M
authors.initials: DM
authors.lastname: Hartley
authors.forename: Thomas
authors.initials: T
authors.lastname: Walz
authors.forename: Peter T
authors.initials: PT
authors.lastname: Lansbury
authors.forename: Ronald
authors.initials: R
authors.lastname: Wetzel
mesh_terms: D000544:Alzheimer Disease / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D041961:Deuterium Exchange Measurement / Q000379:methods; D006801:Humans; D006859:Hydrogen / Q000737:chemistry*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D012995:Solubility; D021241:Spectrometry, Mass, Electrospray Ionization; D013329:Structure-Activity Relationship
chemical_list: D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); D006859:Hydrogen