| Aspect | Key statement | Organism relevance | Main evidence source with citation id(s) | Publication year | DOI/URL |
|---|---|---|---|---|---|
| Identity / synonyms | UniProt P50503 corresponds to **Rattus norvegicus St13**, encoding **Hsc70-interacting protein (Hip)**; literature also uses **ST13**, **Hip**, and **p48**. This matches the requested rat co-chaperone rather than an unrelated ST13 symbol. | Rat-focused; identity supported by rat Hip structural/biochemical literature and conserved mammalian nomenclature | Shi et al. review identifying ST13 as Hip/p48 and noting strong rat-human homology; rat Hip structural study summary (pqac-00000012, pqac-00000016, pqac-00000017) | 2007, 2013, 2021 | https://doi.org/10.1631/jzus.2007.b0170 ; https://doi.org/10.1038/nsmb.2608 ; https://doi.org/10.1177/1535370221999812 |
| Domains | Hip/ST13 is a multidomain co-chaperone with an **N-terminal dimerization region (Hip_N)**, a **central TPR domain** that mediates Hsp70 binding, acidic/charged linker segments, and a **C-terminal GGMP / STI1-HOP_DP-like region with DP motifs**. | Domain architecture is conserved across mammalian Hip proteins; rat structural work directly supports TPR-based binding | Domain/mechanistic reviews and rat Hip structure summaries (pqac-00000012, pqac-00000014, pqac-00000016, pqac-00000017) | 2007, 2013, 2021 | https://doi.org/10.1631/jzus.2007.b0170 ; https://doi.org/10.1038/nsmb.2608 ; https://doi.org/10.1177/1535370221999812 |
| Molecular function | ST13/Hip is a **cytosolic Hsp70/Hsc70 co-chaperone** that promotes productive protein folding by stabilizing chaperone-client complexes; it is not an enzyme or transporter and does not catalyze a chemical reaction. | Broadly conserved in eukaryotes; directly relevant to rat because rat Hip structures define the mechanism | Reviews and structural synthesis describing Hip as a positive Hsp70 co-factor (pqac-00000012, pqac-00000016, pqac-00000017, pqac-00000018) | 2007, 2013, 2021 | https://doi.org/10.1631/jzus.2007.b0170 ; https://doi.org/10.1038/nsmb.2608 ; https://doi.org/10.1177/1535370221999812 |
| Mechanism in Hsp70 cycle | Hip binds the **Hsp70 nucleotide-binding domain (NBD)** preferentially in the **ADP-bound state**, forms a TPR-domain “**bracket**” over the NBD, restrains NBD dynamics, **slows ADP dissociation**, and thereby **delays substrate release**. Hip and nucleotide-exchange factors bind mutually exclusively. | Mechanistic core comes from **rat Hip** crystal structures and mammalian biochemistry; highly applicable to rat P50503 | Rat Hip/Hsp70 structural evidence and mechanistic reviews (pqac-00000000, pqac-00000015, pqac-00000017) | 2013, 2021 | https://doi.org/10.1038/nsmb.2608 ; https://doi.org/10.1177/1535370221999812 |
| Interaction partners | Established partners include **Hsc70/Hsp70**, functional interplay with **Hsp40/DNAJ proteins**, competition with **BAG1** and other NEFs, cooperation/contrast with **HOP/STI1** and **CHIP/STUB1**, and in some contexts direct association with substrates such as **CXCR2** and aggregation-prone proteins such as **α-synuclein**. | Mostly mammalian rather than rat-specific interaction evidence, but consistent with rat Hip sequence/domain conservation | Reviews and disease-mechanism papers (pqac-00000002, pqac-00000003, pqac-00000014, pqac-00000016, pqac-00000018) | 2007, 2009, 2013 | https://doi.org/10.1631/jzus.2007.b0170 ; https://doi.org/10.1038/emboj.2009.298 ; https://doi.org/10.1038/nsmb.2608 |
| Localization | ST13/Hip is best supported as a **cytosolic** protein acting in the **cytosolic Hsp70 protein-quality-control network** and in cytosolic steroid-receptor maturation complexes. | Primarily inferred from mammalian cell biology/reviews; no strong rat-specific subcellular localization paper was recovered here | Cytosolic designation and receptor-complex context from reviews (pqac-00000012, pqac-00000016, pqac-00000018) | 2007, 2013 | https://doi.org/10.1631/jzus.2007.b0170 ; https://doi.org/10.1038/nsmb.2608 |
| Pathways / processes | Principal pathway assignment is **cytosolic proteostasis / protein quality control**, especially the **Hsp70 chaperone cycle** controlling folding, refolding, and substrate fate. Additional implicated processes include **steroid receptor maturation** and suppression of toxic protein aggregation. | Conserved mammalian pathway role; rat relevance strong because rat Hip defines the structural mechanism within the Hsp70 cycle | Hsp70 network review and Hip studies (pqac-00000007, pqac-00000014, pqac-00000017) | 2007, 2013, 2021 | https://doi.org/10.1631/jzus.2007.b0170 ; https://doi.org/10.1038/nsmb.2608 ; https://doi.org/10.1177/1535370221999812 |
| Disease links | Hip/ST13 has been discussed in **neurodegeneration** because it stabilizes Hsp70–α-synuclein complexes and can reduce toxic aggregation; older literature also discussed possible **tumor-suppressor / colorectal cancer** relevance, though evidence was considered incomplete and context-dependent. | Disease links are mostly from human/cell-model or non-rat systems; should be treated as ortholog-informed rather than rat-specific function | Parkinson’s disease proteostasis study and ST13 review (pqac-00000001, pqac-00000002, pqac-00000004, pqac-00000007) | 2007, 2009 | https://doi.org/10.1631/jzus.2007.b0170 ; https://doi.org/10.1038/emboj.2009.298 |
| 2023–2024 developments / applications | Direct 2023–2024 rat St13 functional papers were **not recovered**. Recent mentions are mainly **omics/proteomics** contexts rather than mechanism papers: ST13 appeared among retained host-cell proteins in AAV purification workflows, and a 2023 developmental-genetics study cited ST13 as an Hsc70-interacting protein candidate in pancreas-related regulatory analyses. These are useful as implementation/biomarker contexts but do **not materially revise core function**. | Recent evidence is non-rat mechanistic and mostly human/bioprocessing context; limited direct applicability beyond expression/assay relevance | 2024 AAV host-cell protein proteomics and 2023 eQTL study mention ST13 (pqac-00000008) | 2023, 2024 | https://doi.org/10.1016/j.omtm.2024.101383 ; https://doi.org/10.1038/s41467-023-42560-4 |
| Quantitative data | Reported quantitative features include: Hip binds **ADP-Hsp70 preferentially** with **KD ≈ 8 µM**, weaker binding to apo-Hsp70 (**KD ≈ 51 µM**), and no detectable binding to ATP-Hsp70 under the cited conditions; competing NEFs bind more tightly (**~0.1 µM**). Hip is described as a **~41–43 kDa** protein, dimeric in solution, with estimated abundance around **~1 µM in reticulocyte lysate**. Structural resources include rat Hip/Hsp70 complex entries **4J8D, 4J8E, 4J8F**. | Quantitative binding/mechanistic data derive from mammalian/rat Hip structural biochemistry and are highly relevant to rat P50503 | Structural/biophysical analyses and review synthesis (pqac-00000015, pqac-00000016, pqac-00000017) | 2013, 2021 | https://doi.org/10.1038/nsmb.2608 ; https://doi.org/10.1177/1535370221999812 |


*Table: This table summarizes the verified identity, domain architecture, molecular mechanism, localization, pathways, disease links, recent developments, and quantitative evidence for rat St13/HIP (UniProt P50503). It distinguishes rat-direct evidence from broader mammalian ortholog evidence so the final annotation can stay specific and well-supported.*