| Aspect | Evidence summary | Key source(s) with year, URL, and context citation IDs |
|---|---|---|
| identity/domains | SSA2 matches the target protein as a **Saccharomyces cerevisiae cytosolic Ssa Hsp70** and is one of four SSA-family Hsp70 isoforms (Ssa1–4); Ssa1/2 are constitutive, whereas Ssa3/4 are stress inducible. Hsp70 functional architecture is supported by evidence that the **N-terminal nucleotide-binding domain (NBD)** mediates ATPase regulation and the **C-terminal region** contributes to substrate transfer/isoform specificity; the cited work maps functional distinction between Ssa2 and Ssa4 largely to the C-terminal domain. (pqac-00000001, pqac-00000000, pqac-00000006, pqac-00000007) | Gaur et al., 2020, *Genetics*, https://doi.org/10.1534/genetics.120.303190 (pqac-00000000, pqac-00000001, pqac-00000006, pqac-00000007) |
| biochemical activity | SSA2 is an **ATP-dependent molecular chaperone** of the Hsp70 family that binds ATP and acts with **Hsp40 cochaperones** and **nucleotide exchange factors** to prevent aggregation, assist folding/refolding, and support degradation/translocation of client proteins. Experimental handling of purified Ssa2 with ATP-agarose and mechanistic interpretation of Ydj1 action support ATP-linked chaperone cycling rather than enzyme-like substrate conversion. (pqac-00000001, pqac-00000003, pqac-00000004, pqac-00000005) | Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (pqac-00000001, pqac-00000003); Matveenko et al., 2025, https://doi.org/10.17816/ecogen676918 (pqac-00000004, pqac-00000005) |
| localization | The strongest direct localization evidence in the provided context places SSA2 in the **cytosol**. Tagged Ssa proteins, including Ssa2, showed a predominantly **diffuse cytosolic distribution** in fluorescence microscopy, and Gaur et al. also describe SSA2 as a cytosolic Hsp70 acting upstream of Hsp90. (pqac-00000006, pqac-00000007, pqac-00000009) | Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (pqac-00000006, pqac-00000007); Matveenko et al., 2025, https://doi.org/10.17816/ecogen676918 (pqac-00000009) |
| pathways/complexes | SSA2 functions in the **Hsp70–Hsp90 chaperone pathway**, where Ydj1 recruits misfolded clients to Hsp70 and promotes transfer toward Hsp90-dependent maturation; Ssa2 supports this process better than Ssa4. In proteostasis compartment biology, Ssa1/Ssa2 are required for **JUNQ sorting/localization to the nucleus–vacuole junction (NVJ)** and for clearance of cytoplasmic misfolded proteins, with Btn2 favoring JUNQ sorting, Hsp42 favoring IPOD sorting, and Atg1/Atg8 plus Nvj1/Vac8 implicated in JUNQ clearance via microautophagy-related mechanisms. (pqac-00000002, pqac-00000003, pqac-00000010, pqac-00000011, pqac-00000012, pqac-00000013) | Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (pqac-00000002, pqac-00000003); Rolli et al., 2024, *Front. Mol. Biosci.*, https://doi.org/10.3389/fmolb.2024.1427542 (pqac-00000010, pqac-00000011, pqac-00000012, pqac-00000013) |
| recent 2023-2024 findings | In a 2024 heat-shock feedback study, **SSA2 had the highest expression rank** among SSA paralogs in the reported reporter dataset (Ssa3 < Ssa4 < Ssa1 < Ssa2), and deleting the Hsf1-binding site at SSA2 altered Hsf1 reporter behavior, consistent with SSA2 contributing to **basal repression/feedback control** of Hsf1-regulated heat-shock expression. A separate 2024 study showed that loss of Ssa1/Ssa2 shifts cytoplasmic misfolded-protein management away from JUNQ and toward IPOD-like inclusions, linking SSA2 to modern models of spatial proteostasis. (pqac-00000008, pqac-00000010, pqac-00000011, pqac-00000012) | Garde et al., 2024, *bioRxiv*, https://doi.org/10.1101/2024.01.09.574867 (pqac-00000008); Rolli et al., 2024, https://doi.org/10.3389/fmolb.2024.1427542 (pqac-00000010, pqac-00000011, pqac-00000012) |
| quantitative/statistical data | Quantitative findings in the provided context include: **Ydj1-assisted luciferase refolding was ~25–30× higher with Ssa2 than Ssa4** in the Hsp90-client study; in the heat-shock feedback study, **six** ΔHSE mutants had significantly increased and **three** had significantly reduced HSE-YFP after 4 h heat shock (**p < 0.05**), with **ssa2ΔHSE** among mutants showing elevated basal reporter signal; and in JUNQ studies, NES-LuciTs degradation phenotypes showed significant differences (**P = 0.0061** and **P = 0.0392** in unpaired t-tests), while **50 μM bortezomib** did not significantly alter NES-LuciTs degradation in one assay and NES-VHL cleared in about **half the time** of NES-Luci. (pqac-00000000, pqac-00000008, pqac-00000010, pqac-00000012) | Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (pqac-00000000); Garde et al., 2024, https://doi.org/10.1101/2024.01.09.574867 (pqac-00000008); Rolli et al., 2024, https://doi.org/10.3389/fmolb.2024.1427542 (pqac-00000010, pqac-00000012) |
| applications | Within the provided evidence, SSA2 is most useful as a **model proteostasis factor** for dissecting client maturation, stress-response feedback, prion biology, and spatial quality control rather than as a dedicated metabolic enzyme or transporter. The studies use SSA2 in practical experimental contexts including purified chaperone biochemistry, isoform-swapping to map domain specificity, and reporter-based assays for misfolded-protein clearance and heat-shock regulation. (pqac-00000000, pqac-00000002, pqac-00000005, pqac-00000008, pqac-00000011) | Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (pqac-00000000, pqac-00000002); Matveenko et al., 2025, https://doi.org/10.17816/ecogen676918 (pqac-00000005); Garde et al., 2024, https://doi.org/10.1101/2024.01.09.574867 (pqac-00000008); Rolli et al., 2024, https://doi.org/10.3389/fmolb.2024.1427542 (pqac-00000011) |


*Table: This table summarizes identity, activity, localization, pathways, recent findings, quantitative data, and practical research uses for yeast SSA2 (UniProt P10592/YLL024C) using only the provided evidence contexts. It is useful as a compact evidence map for functional annotation and literature-backed reporting.*