From guide to guard—activation mechanism of the stress-sensing chaperone Get3
--Kathrin Ulrich, Ákos Farkas, Olivia Chan, Olivia Katamanin, Blanche Schwappach, Ursula Jakob
HIGHLIGHTS:
•Oxidative activation of Get3’s chaperone function is a tightly orchestrated process
•Crucial cysteine pair links ROS-induced activation to nucleotide-binding state
•Effective client recovery requires reductive Get3 inactivation and foldase systems
•Failure to properly inactivate Get3 impairs oxidative stress resistance in yeast
SUMMARY:
Oxidative stress conditions can cause ATP depletion, oxidative protein unfolding, and potentially toxic protein aggregation. To alleviate this proteotoxic stress, the highly conserved yeast protein, Get3, switches from its guiding function as an ATP-dependent targeting factor for tail-anchored proteins to its guarding function as an ATP-independent molecular chaperone that prevents irreversible protein aggregation. Here, we demonstrate that activation of Get3’s chaperone function follows a tightly orchestrated multi-step process, centered around the redox status of two conserved cysteines, whose reactivity is directly controlled by Get3’s nucleotide-binding state. Thiol oxidation causes local unfolding and the transition into chaperone-active oligomers. Vice versa, inactivation requires the reduction of Get3’s cysteines followed by ATP-binding, which allows the transfer of bound client proteins to ATP-dependent chaperone systems for their effective refolding. Manipulating this fine-tuned cycle of activation and inactivation in yeast impairs oxidative stress resistance and growth, illustrating the necessity to tightly control Get3’s intrinsic chaperone function.
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