Biology subjects

Gestaut, D.

Publications and source records attributed to Gestaut, D..

2 recordsLinked to original sources

bioRxiv2023

A structural vista of phosducin-like PhLP2A-chaperonin TRiC cooperation during the ATP-driven folding cycle

Proper cellular proteostasis, essential for viability, requires a network of chaperones and cochaperones. ATP-dependent chaperonin TRiC/CCT partners with cochaperones prefoldin (PFD) and phosducin-like proteins (PhLPs) to facilitate the folding of essential eukaryotic proteins. Using cryoEM and biochemical analyses, we determine the ATP-driven cycle of TRiC-PFD-PhLP2A interaction. In the open TRiC state, PhLP2A binds to the chambers equator while its N-terminal H3-domain binds to the apical domains of CCT3/4, thereby displacing PFD from TRiC. ATP-induced TRiC closure rearranges the contacts of PhLP2A domains within the closed chamber. In the presence of substrate, actin and PhLP2A segregate into opposing chambers, each binding to the positively charged inner surfaces formed by CCT1/3/6/8. Notably, actin induces a conformational change in PhLP2A, causing its N-terminal helices to extend across the inter-ring interface to directly contact a hydrophobic groove in actin. Our findings reveal an ATP-driven PhLP2A structural rearrangement cycle within the TRiC chamber to facilitate folding. Highlights- Structural analysis of TRiC-mediated folding cycle with cochaperones PhLP2A and PFD. - The interactions of PhLP2A and PFD with TRiC are mutually exclusive. - PhLP2A domains interact in a subunit-specific manner with the TRiC chamber. - PhLP2A domains are rearranged in ATP-closed TRiC to contact actin across the ring interface

biophysics↗

bioRxiv2022

Ribotoxic collisions on CAG expansions disrupt proteostasis and stress responses in Huntington's Disease

Huntingtons disease (HD) is a devastating neurodegenerative disorder caused by CAG trinucleotide repeat expansions encoding a polyglutamine (polyQ) tract in the Huntingtin (HTT) gene1. Although mutant HTT (mHTT) protein tends to aggregate, the exact causes of neurotoxicity in HD remain unclear2. Here we show that altered elongation kinetics on CAG expansions cause ribosome collisions that trigger ribotoxicity, proteotoxicity and maladaptive stress responses. CAG expansions cause an elongation rate conflict during HTT translation, when ribosomes rapidly decoding the optimal polyQ encounter a flanking slowly-decoded polyproline tract. The ensuing ribosome collisions lead to premature termination and release of aggregation-prone mHTT fragments. Due to the presence of a stress-responsive upstream open reading frame (uORF), HTT translation and aggregation are limited under normal conditions but enhanced under stress, seeding a vicious cycle of dysfunction. mHTT further exacerbates ribotoxicity by progressively sequestering eIF5A, a key regulator of translation elongation, polyamine metabolism and stress responses. eIF5A depletion in HD cells leads to widespread ribosome pausing on eIF5A-dependent sites, impaired cotranslational proteostasis, disrupted polyamine metabolism and maladaptive stress responses. Importantly, drugs that reduce translation initiation attenuate ribosome collisions and mitigate this escalating cascade of ribotoxic stress and dysfunction in HD.

neuroscience↗