Atomic force microscopy analysis of the Huntington protein nanofibril formation.
BACKGROUND
Huntington's disease is an autosomal dominant progressive neurodegenerative disease associated with dramatic expansion of a polyglutamine sequence in exon 1 of the huntingtin protein htt that leads to cytoplasmic, and even nuclear aggregation of fibrils.


METHODS
We have studied the in vitro fibril formation of mutant exon 1, and the shorter wild-type exon 1, with use of atomic force microscopy (AFM).


RESULTS
Large aggregates are formed spontaneously after cleavage of the glutathione-S-transferase fusion protein of the mutant exon 1 protein. The AFM data showed that, unlike fibrils assembled by such proteins as amyloid beta-peptide and alpha-synuclein, htt forms fibrils with extensive branched morphologic features. Branching can be observed even at earlier stages of the htt self-assembly, but the effect is much more pronounced at late stages of aggregation. We also found that fusing of htt with green fluorescent protein does not change the branched-type morphologic features of the aggregates.


CONCLUSIONS
On the basis of the results obtained, we propose a model for htt fibrillization that explains branched morphologic features of the aggregates.
Dahlgren
Paul R
PR
School of Life Sciences, Arizona State University, Tempe, Arizona, USA.
Karymov
Mikhail A
MA
Bankston
John
J
Holden
Tina
T
Thumfort
Peter
P
Ingram
Vernon M
VM
Lyubchenko
Yuri L
YL
D003198:Computer Simulation; D003460:Crystallization / Q000379:methods; D019281:Dimerization; D000071058:Huntingtin Protein; D018625:Microscopy, Atomic Force / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000648:ultrastructure; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D009687:Nuclear Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D011485:Protein Binding; D011487:Protein Conformation
C506812:Htt protein, mouse; D000071058:Huntingtin Protein; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins