Selective observation of semi-rigid non-core residues in dynamically complex mutant huntingtin protein fibrils

Irina Matlahov, Jennifer C. Boatz, Patrick C.A. van der Wel

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Many amyloid-forming proteins, which are normally intrinsically disordered, undergo a disorder-to-order transition to form fibrils with a rigid β-sheet core flanked by disordered domains. Solid-state NMR (ssNMR) and cryogenic electron microscopy (cryoEM) excel at resolving the rigid structures within amyloid cores but studying the dynamically disordered domains remains challenging. This challenge is exemplified by mutant huntingtin exon 1 (HttEx1), which self-assembles into pathogenic neuronal inclusions in Huntington disease (HD). The mutant protein's expanded polyglutamine (polyQ) segment forms a fibril core that is rigid and sequestered from the solvent. Beyond the core, solvent-exposed surface residues mediate biological interactions and other properties of fibril polymorphs. Here we deploy magic angle spinning ssNMR experiments to probe for semi-rigid residues proximal to the fibril core and examine how solvent dynamics impact the fibrils’ segmental dynamics. Dynamic spectral editing (DYSE) 2D ssNMR based on a combination of cross-polarization (CP) ssNMR with selective dipolar dephasing reveals the weak signals of solvent-mobilized glutamine residues, while suppressing the normally strong background of rigid core signals. This type of ‘intermediate motion selection’ (IMS) experiment based on cross-polarization (CP) ssNMR, is complementary to INEPT- and CP-based measurements that highlight highly flexible or highly rigid protein segments, respectively. Integration of the IMS-DYSE element in standard CP-based ssNMR experiments permits the observation of semi-rigid residues in a variety of contexts, including in membrane proteins and protein complexes. We discuss the relevance of semi-rigid solvent-facing residues outside the fibril core to the latter's detection with specific dyes and positron emission tomography tracers.

Original languageEnglish
Article number100077
JournalJournal of Structural Biology: X
Volume6
DOIs
StatePublished - Jan 2022
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2022

Funding

This work was supported by the National Institutes of Health (grants R01 GM112678 and R01 GM113908 to PvdW; T32 GM088119 to J.C.B), the Achievement Rewards for College Scientists (ARCS) Foundation (J.C.B.), the CHDI Foundation, and the CampagneTeam Huntington foundation.

FundersFunder number
CampagneTeam Huntington foundation
National Institutes of HealthR01 GM113908, R01 GM112678, T32 GM088119
CHDI Foundation

    Keywords

    • Dynamics
    • Huntington's disease
    • Intermediate-timescale motion
    • Polyglutamine
    • Solid state NMR

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