title: Abeta40-Lactam(D23/K28) models a conformation highly favorable for nucleation of amyloid.
abstract: Recent solid-state NMR data (1) demonstrate that Abeta(1)(-)(40) adopts a conformation in amyloid fibrils with two in-register, parallel beta-sheets, connected by a bend structure encompassing residues D(23)VGSNKG(29), with a close contact between the side chains of Asp23 and Lys28. We hypothesized that forming this bend structure might be rate-limiting in fibril formation, as indicated by the lag period typically observed in the kinetics of Abeta(1)(-)(40) fibrillogenesis. We synthesized Abeta(1)(-)(40)-Lactam(D23/K28), a congener Abeta(1)(-)(40) peptide that contains a lactam bridge between the side chains of Asp23 and Lys28. Abeta(1)(-)(40)-Lactam(D23/K28) forms fibrils similar to those formed by Abeta(1)(-)(40). The kinetics of fibrillogenesis, however, occur without the typical lag period, and at a rate approximately 1000-fold greater than is seen with Abeta(1)(-)(40) fibrillogenesis. The strong tendency toward self-association is also shown by size exclusion chromatography in which Abeta(1)(-)(40)-Lactam(D23/K28) forms oligomers even at concentrations of approximately 1-5 microM. Under the same conditions, Abeta(1)(-)(40) shows no detectable oligomers by size exclusion chromatography. Our data suggest that Abeta(1)(-)(40)-Lactam(D23/K28) could bypass an unfavorable folding step in fibrillogenesis, because the lactam linkage "preforms" a bendlike structure in the peptide. Consistent with this view Abeta(1)(-)(40) growth is efficiently nucleated by Abeta(1)(-)(40)-Lactam(D23/K28) fibril seeds.
authors.affiliation: Departments of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Kimberly L
authors.initials: KL
authors.lastname: Sciarretta
authors.forename: David J
authors.initials: DJ
authors.lastname: Gordon
authors.forename: Aneta T
authors.initials: AT
authors.lastname: Petkova
authors.forename: Robert
authors.initials: R
authors.lastname: Tycko
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Meredith
mesh_terms: D000595:Amino Acid Sequence; D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D016229:Amyloid beta-Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000648:ultrastructure; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D007769:Lactams / Q000138:chemical synthesis / Q000737:chemistry; D008854:Microscopy, Electron; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry* / Q000648:ultrastructure; D011487:Protein Conformation; D013053:Spectrophotometry
chemical_list: D000682:Amyloid; D016229:Amyloid beta-Peptides; D007769:Lactams; D046912:Multiprotein Complexes; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40)