Conformational dynamics and self-association of intrinsically disordered Huntingtin exon 1 in cells

Abstract

Huntington's disease is caused by a CAG trinucleotide expansion mutation in the Huntingtin gene that leads to an artificially long polyglutamine sequence in the Huntingtin protein. A key feature of the disease is the intracellular aggregation of the Huntingtin exon 1 protein (Htt) into micrometer sized inclusion bodies. The aggregation process of Htt has been extensively studied in vitro, however, the crucial early events of nucleation and aggregation in the cell remain elusive. Here, we studied the conformational dynamics and self-association of Htt by in-cell experiments using laser-induced temperature jumps and analytical ultracentrifugation. Both short and long polyglutamine variants of Htt underwent an apparent temperature-induced conformational collapse. The temperature jumps generated a population of kinetically trapped species selectively for the longer polyglutamine variants of Htt proteins. Their occurrence correlated with the formation of inclusion bodies suggesting that such species trigger further self-association.

Temperature-induced collapse of a disordered peptide observed by three sampling methods in molecular dynamics simulations

“…Our simulations over a range of temperatures produced a temperature-induced collapse for Q15, in agreement with recent experimental observations on polyQ tracks in the Htt exon-1 domain 36 and on other IDPs. Many hypotheses have been proposed to explain the temperature-induced collapse, including strengthened hydrophobic interactions, 36 weakened solvation, 44 reduced thermal fluctuations, 40 melting of PPII helices, 62 and others. 38,69 In a recent study, Zerze et al 38 simulated 5 different IDPs with different amino acid compositions.…”

“…More interestingly, recent temperature jump experiments showed a temperature-induced collapse for polyQ tracks of various lengths contained in the Htt exon-1 domain. 36 This observation provides direct support for our temperaturedependent simulation results.…”

“…[25][26][27] Directly relevant to the present study, polyQ tracks in the Htt exon-1 domain were found in recent temperature jump experiments to show monotonic temperature-induced collapse. 36 Various enhanced sampling techniques have been applied to the study of IDPs. 3,[37][38][39][40][41] One of the most notable is TREMD, 7 which involves a set of replicate simulations that spans a temperature range between the temperature of interest and an artificially high temperature.…”

The 17-residue-long N terminus in huntingtin controls stepwise aggregation in solution and on membranes via different mechanisms

“…Because of its role in disease and its potential importance in the development of therapeutics, the mechanism of Httex1 aggregation has been of significant interest (13)(14)(15)(16)(17)(18). Httex1 has three domains, an N terminus containing 17 amino acids (N17), a polyQ region of variable length (polyQ), and a C-terminal proline-rich domain (PRD).…”

Inhibition of Huntingtin Exon-1 Aggregation by the Molecular Tweezer CLR01

“…Further, we used a recently developed in-cell kinetic aggregation assay in which htt e1 aggregation is induced by tailored infrared laser heating pulses. 22 HeLa cells were incubated for 24 hours with the compounds and transfected with a ${\text{htt}}_{\mathrm{Q}55}^{\mathrm{e}1}$ intermolecular FRET reporter (see SI for details). Aggregation in single cells was induced and imaged by FRET microscopy 16 h past transfection.…”