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Tsa1 is the major cytosolic typical 2-Cys peroxiredoxin of budding yeast,
with peroxidatic Cys48 (CP) and resolving Cys171 (CR) forming an
inter-subunit disulfide during the catalytic cycle.
"The research target is the budding yeast (*Saccharomyces cerevisiae*) protein **Tsa1**, consistently described across primary and review sources as the **major cytosolic typical 2‑Cys peroxiredoxin** (Prx) with canonical active-site cysteines **Cys48 (peroxidatic, CP)** and **Cys171 (resolving, CR)**."
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Tsa1 is a thioredoxin-dependent peroxidase that reduces H2O2 and organic
hydroperoxides; oxidized Tsa1 disulfide is reduced by the cytosolic
thioredoxin system (Trx1/Trx2, recycled by thioredoxin reductase using
NADPH).
"Tsa1 reduces **H2O2 and organic hydroperoxides**; in typical 2‑Cys Prxs this occurs via CP attack on the peroxide bond, generating water/alcohol products."
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Reduction of oxidized Tsa1 is driven primarily by the cytosolic
thioredoxin system.
"Reduction of oxidized Tsa1 is primarily driven by the **cytosolic thioredoxin system**: **Trx1/Trx2** reduce the Tsa1 disulfide, and oxidized thioredoxin is recycled by **thioredoxin reductase** using **NADPH**."
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Because of high abundance (~1% of cytosolic protein, ~10-50 uM) and fast
kinetics, peroxiredoxins decompose the majority of cellular hydroperoxides.
"Reviews also emphasize that Prxs decompose **>90% of cellular hydroperoxides** and can detoxify up to **~90% of cytosolic H2O2** due to abundance and fast reaction rates (general Prx second-order rates ~10^6–10^8 M−1 s−1)."
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At high oxidant loads the peroxidatic cysteine hyperoxidizes
(sulfinic/sulfonic), inactivating peroxidase activity and promoting
higher-order oligomers with molecular chaperone/holdase activity.
"At higher oxidant loads, Tsa1’s peroxidatic cysteine can become **hyperoxidized** (sulfinic/sulfonic states), which **inactivates peroxidase activity** and promotes formation of **higher-order oligomers** associated with **molecular chaperone/holdase activity**."
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Increased Tsa1 dosage extends replicative lifespan in a manner dependent on
Hsp70 (Ssa1/2) and partly Hsp104, and requires reduction of hyperoxidized
Tsa1 by sulfiredoxin Srx1, supporting a role as a stress-activated
chaperone adaptor that recruits protein quality control machinery.
"Increased dosage of Tsa1 extends replicative lifespan in a manner dependent on **Hsp70 (Ssa1/2)** and partly on **Hsp104**, and requires reduction of hyperoxidized Tsa1 by **sulfiredoxin Srx1** for aggregate clearance/disaggregation."
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Tsa1 contributes to stress resistance and longevity partly through redox
repression of the Ras-cAMP-PKA pathway, oxidizing a conserved cysteine
(Cys243) of the PKA catalytic subunit and blocking activation-loop Thr241
phosphorylation.
"Specifically, Tsa1 represses the **Ras–cAMP–PKA pathway** by promoting oxidative modifications of PKA catalytic subunits; redox modification of a conserved cysteine (reported as **Cys243** in the catalytic subunit) inhibits phosphorylation of **Thr241** in the activation loop and reduces kinase activity."
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tsa1-null cells show a mutator phenotype (~5-10-fold increased mutation
rates); Tsa1 is the strongest suppressor of mutations among oxidant-defense
genes in yeast, with genome protection involving both peroxidase-dependent
and peroxidase-independent (redox-network) facets.
"Yeast lacking TSA1 show a **mutator phenotype**, with reported **~5–10‑fold increased mutation rates**, and Tsa1 is described as the strongest suppressor of mutations among oxidant-defense genes in yeast."
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Tsa1 is the major cytosolic peroxiredoxin and is additionally found
associated with translating ribosomes, placing it near nascent
polypeptides for translation-linked proteostasis.
"In addition to a free cytosolic pool, one source reports Tsa1 is also found **associated with translating ribosomes**, suggesting functional proximity to nascent polypeptides and translation-linked proteostasis."
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Tsa1 forms widespread covalent mixed-disulfide intermediates (TIMDIs,
"peroxiredoxinylation") with client proteins via the peroxidatic cysteine;
thioredoxins directly remove these adducts, extending the
thioredoxin-peroxiredoxin system into a proteome-thiol buffering circuit.
"A 2023 bioRxiv preprint reports that Tsa1 forms widespread covalent mixed disulfide intermediates with cellular proteins, termed **Tsa1-Induced Mixed Disulfide Intermediates (TIMDIs)**, and frames this as a bona fide redox-linked post-translational modification termed **peroxiredoxinylation**."