Structural Mechanisms of Mutant Huntingtin Aggregation Suppression by the Synthetic Chaperonin-like CCT5 Complex Explained by Cryoelectron Tomography

J Biol Chem. 2015 Jul 10;290(28):17451-61. doi: 10.1074/jbc.M115.655373. Epub 2015 May 20.

Abstract

Huntington disease, a neurodegenerative disorder characterized by functional deficits and loss of striatal neurons, is linked to an expanded and unstable CAG trinucleotide repeat in the huntingtin gene (HTT). This DNA sequence translates to a polyglutamine repeat in the protein product, leading to mutant huntingtin (mHTT) protein aggregation. The aggregation of mHTT is inhibited in vitro and in vivo by the TCP-1 ring complex (TRiC) chaperonin. Recently, a novel complex comprised of a single type of TRiC subunit has been reported to inhibit mHTT aggregation. Specifically, the purified CCT5 homo-oligomer complex, when compared with TRiC, has a similar structure, ATP use, and substrate refolding activity, and, importantly, it also inhibits mHTT aggregation. Using an aggregation suppression assay and cryoelectron tomography coupled with a novel computational classification method, we uncover the interactions between the synthetic CCT5 complex (∼ 1 MDa) and aggregates of mutant huntingtin exon 1 containing 46 glutamines (mHTTQ46-Ex1). We find that, in a similar fashion to TRiC, synthetic CCT5 complex caps mHTT fibrils at their tips and encapsulates mHTT oligomers, providing a structural description of the inhibition of mHTTQ46-Ex1 by CCT5 complex and a shared mechanism of mHTT inhibition between TRiC chaperonin and the CCT5 complex: cap and contain.

Keywords: CCT5 complex; Huntington disease; chaperonin; cryoelectron microscopy; electron tomography; protein aggregation; single-particle tomography.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chaperonin Containing TCP-1 / chemistry*
  • Chaperonin Containing TCP-1 / genetics
  • Chaperonin Containing TCP-1 / ultrastructure
  • Cryoelectron Microscopy
  • Electron Microscope Tomography
  • Humans
  • Huntingtin Protein
  • Huntington Disease / genetics
  • Huntington Disease / metabolism
  • Models, Molecular
  • Mutant Proteins / chemistry*
  • Mutant Proteins / genetics
  • Mutant Proteins / ultrastructure
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / ultrastructure
  • Protein Aggregates
  • Protein Aggregation, Pathological / genetics
  • Protein Aggregation, Pathological / metabolism
  • Protein Interaction Domains and Motifs
  • Protein Structure, Quaternary
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / ultrastructure

Substances

  • CCT5 protein, human
  • HTT protein, human
  • Huntingtin Protein
  • Mutant Proteins
  • Nerve Tissue Proteins
  • Protein Aggregates
  • Recombinant Proteins
  • Chaperonin Containing TCP-1