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2014 ; 53
(42
): 6653-66
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Polyglutamine amyloid core boundaries and flanking domain dynamics in huntingtin
fragment fibrils determined by solid-state nuclear magnetic resonance
#MMPMID25280367
Hoop CL
; Lin HK
; Kar K
; Hou Z
; Poirier MA
; Wetzel R
; van der Wel PC
Biochemistry
2014[Oct]; 53
(42
): 6653-66
PMID25280367
show ga
In Huntington's disease, expansion of a polyglutamine (polyQ) domain in the
huntingtin (htt) protein leads to misfolding and aggregation. There is much
interest in the molecular features that distinguish monomeric, oligomeric, and
fibrillar species that populate the aggregation pathway and likely differ in
cytotoxicity. The mechanism and rate of aggregation are greatly affected by the
domains flanking the polyQ segment within exon 1 of htt. A "protective"
C-terminal proline-rich flanking domain inhibits aggregation by inducing
polyproline II structure (PPII) within an extended portion of polyQ. The
N-terminal flanking segment (htt(NT)) adopts an ?-helical structure as it drives
aggregation, helps stabilize oligomers and fibrils, and is seemingly integral to
their supramolecular assembly. Via solid-state nuclear magnetic resonance
(ssNMR), we probe how, in the mature fibrils, the htt flanking domains impact the
polyQ domain and in particular the localization of the ?-structured amyloid core.
Using residue-specific and uniformly labeled samples, we find that the amyloid
core occupies most of the polyQ domain but ends just prior to the prolines. We
probe the structural and dynamical features of the remarkably abrupt ?-sheet to
PPII transition and discuss the potential connections to certain htt-binding
proteins. We also examine the htt(NT) ?-helix outside the polyQ amyloid core.
Despite its presumed structural and demonstrated stabilizing roles in the
fibrils, quantitative ssNMR measurements of residue-specific dynamics show that
it undergoes distinct solvent-coupled motion. This dynamical feature seems
reminiscent of molten-globule-like ?-helix-rich features attributed to the
nonfibrillar oligomeric species of various amyloidogenic proteins.