β-hairpin-mediated nucleation of polyglutamine amyloid formation.
The conformational preferences of polyglutamine (polyQ) sequences are of major interest because of their central importance in the expanded CAG repeat diseases that include Huntington's disease. Here, we explore the response of various biophysical parameters to the introduction of β-hairpin motifs within polyQ sequences. These motifs (tryptophan zipper, disulfide, d-Pro-Gly, Coulombic attraction, l-Pro-Gly) enhance formation rates and stabilities of amyloid fibrils with degrees of effectiveness well correlated with their known abilities to enhance β-hairpin formation in other peptides. These changes led to decreases in the critical nucleus for amyloid formation from a value of n=4 for a simple, unbroken Q23 sequence to approximate unitary n values for similar length polyQs containing β-hairpin motifs. At the same time, the morphologies, secondary structures, and bioactivities of the resulting fibrils were essentially unchanged from simple polyQ aggregates. In particular, the signature pattern of solid-state NMR (13)C Gln resonances that appears to be unique to polyQ amyloid is replicated exactly in fibrils from a β-hairpin polyQ. Importantly, while β-hairpin motifs do produce enhancements in the equilibrium constant for nucleation in aggregation reactions, these Kn values remain quite low (~10(-)(10)) and there is no evidence for significant enhancement of β-structure within the monomer ensemble. The results indicate an important role for β-turns in the nucleation mechanism and structure of polyQ amyloid and have implications for the nature of the toxic species in expanded CAG repeat diseases.
Department of Structural Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Karunakar
K
Kar
Cody L
CL
Hoop
Kenneth W
KW
Drombosky
Matthew A
MA
Baker
Ravindra
R
Kodali
Irene
I
Arduini
Patrick C A
PC
van der Wel
W Seth
WS
Horne
Ronald
R
Wetzel
D000595:Amino Acid Sequence; D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D005091:Exons / Q000235:genetics; D005973:Glutamine / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D000071058:Huntingtin Protein; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016716:PC12 Cells; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D051381:Rats; D017550:Spectroscopy, Fourier Transform Infrared
D000682:Amyloid; C499524:Htt protein, rat; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D005973:Glutamine; D049452:Green Fluorescent Proteins; C097188:polyglutamine