title: N-Terminal Extensions Retard Aβ42 Fibril Formation but Allow Cross-Seeding and Coaggregation with Aβ42.
abstract: Amyloid β-protein (Aβ) sequence length variants with varying aggregation propensity coexist in vivo, where coaggregation and cross-catalysis phenomena may affect the aggregation process. Until recently, naturally occurring amyloid β-protein (Aβ) variants were believed to begin at or after the canonical β-secretase cleavage site within the amyloid β-protein precursor. However, N-terminally extended forms of Aβ (NTE-Aβ) were recently discovered and may contribute to Alzheimer's disease. Here, we have used thioflavin T fluorescence to study the aggregation kinetics of Aβ42 variants with N-terminal extensions of 5-40 residues, and transmission electron microscopy to analyze the end states. We find that all variants form amyloid fibrils of similar morphology as Aβ42, but the half-time of aggregation (t1/2) increases exponentially with extension length. Monte Carlo simulations of model peptides suggest that the retardation is due to an underlying general physicochemical effect involving reduced frequency of productive molecular encounters. Indeed, global kinetic analyses reveal that NTE-Aβ42s form fibrils via the same mechanism as Aβ42, but all microscopic rate constants (primary and secondary nucleation, elongation) are reduced for the N-terminally extended variants. Still, Aβ42 and NTE-Aβ42 coaggregate to form mixed fibrils and fibrils of either Aβ42 or NTE-Aβ42 catalyze aggregation of all monomers. NTE-Aβ42 monomers display reduced aggregation rate with all kinds of seeds implying that extended termini interfere with the ability of monomers to nucleate or elongate. Cross-seeding or coaggregation may therefore represent an important contribution in the in vivo formation of assemblies believed to be important in disease.
authors.affiliation: Department of Biochemistry and Structural Biology, Lund University , P O Box 124, 221 00 Lund, Sweden.
authors.forename: Olga
authors.initials: O
authors.lastname: Szczepankiewicz
authors.affiliation: Department of Biochemistry and Structural Biology, Lund University , P O Box 124, 221 00 Lund, Sweden.
authors.forename: Björn
authors.initials: B
authors.lastname: Linse
authors.affiliation: Department of Chemistry, Cambridge University , Lensfield Road, Cambridge, CB2 1EW, United Kingdom.
authors.forename: Georg
authors.initials: G
authors.lastname: Meisl
authors.affiliation: Department of Biochemistry and Structural Biology, Lund University , P O Box 124, 221 00 Lund, Sweden.
authors.forename: Eva
authors.initials: E
authors.lastname: Thulin
authors.affiliation: Department of Biochemistry and Structural Biology, Lund University , P O Box 124, 221 00 Lund, Sweden.
authors.forename: Birgitta
authors.initials: B
authors.lastname: Frohm
authors.affiliation: Laboratory for Neurodegenerative Research, Conway Institute of Biomedical and Biomolecular Research, University College Dublin , Belfield, Dublin 4, Republic of Ireland.
authors.forename: Carlo
authors.initials: C
authors.lastname: Sala Frigerio
authors.affiliation: Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Colvin
authors.affiliation: Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Angela C
authors.initials: AC
authors.lastname: Jacavone
authors.affiliation: Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Griffin
authors.affiliation: Department of Chemistry, Cambridge University , Lensfield Road, Cambridge, CB2 1EW, United Kingdom.
authors.forename: Tuomas
authors.initials: T
authors.lastname: Knowles
authors.affiliation: Laboratory for Neurodegenerative Research, Conway Institute of Biomedical and Biomolecular Research, University College Dublin , Belfield, Dublin 4, Republic of Ireland.|Laboratory for Neurodegenerative Research, Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School , Boston, Massachusetts 02115, United States.
authors.forename: Dominic M
authors.initials: DM
authors.lastname: Walsh
authors.affiliation: Department of Biochemistry and Structural Biology, Lund University , P O Box 124, 221 00 Lund, Sweden.
authors.forename: Sara
authors.initials: S
authors.lastname: Linse
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D002942:Circular Dichroism; D007700:Kinetics; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D009010:Monte Carlo Method; D010446:Peptide Fragments / Q000737:chemistry*
chemical_list: D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C075222:amyloid beta-protein (1-42)