| Category | Key points | Key evidence (short) | Key citations (pqac IDs) |
|---|---|---|---|
| Identity | Rat **Hspa5** (UniProt **P06761**) corresponds to **BiP/GRP78**, the major **ER-resident HSP70-family chaperone**; evidence from mammalian BiP/GRP78 literature aligns with UniProt family/domain annotation. | Reviews and mechanistic studies consistently define HSPA5/BiP/GRP78 as the principal ER-lumen HSP70 chaperone and UPR regulator. | (pqac-00000000, pqac-00000002, pqac-00000011) |
| Localization | Primary localization is the **ER lumen**; retention depends on the **C-terminal KDEL motif** and KDELR-mediated retrieval. | BiP-FLAG inserted upstream of the essential KDEL signal preserved ER localization/function; reviews describe KDEL-based ER retention and retrieval. | (pqac-00000011, pqac-00000008, pqac-00000010, pqac-00000015) |
| Molecular function | BiP is an **ATP-dependent molecular chaperone** with an **N-terminal nucleotide/ATPase-binding domain** and **C-terminal substrate-binding domain** that binds unfolded polypeptides, maintains folding competence, and prevents aggregation. | Review/mechanistic evidence describes peptide-dependent ATPase cycle; residue/domain-level summaries place ATPase/NBD in the N-terminus and substrate-binding activity in the C-terminus/interdomain linker-regulated cycle. | (pqac-00000002, pqac-00000011, pqac-00000016) |
| UPR regulation | BiP negatively regulates the three canonical UPR sensors **IRE1, PERK, and ATF6** under basal conditions; ER stress sequesters BiP onto misfolded proteins, allowing sensor activation. | Reviews describe dissociation from sensors during stress; in vivo AP-MS showed basal binding to IRE1α and PERK with release after tunicamycin. | (pqac-00000000, pqac-00000002, pqac-00000006, pqac-00000011, pqac-00000015) |
| ERAD & proteostasis | BiP is central to **ER proteostasis**, recognizing unfolded/misfolded proteins and contributing to **ERAD-linked quality control** and broader degradation routing. | ER chaperones including BiP recognize ERAD substrates; BiP-client binding is a surrogate for ER misfolding, with misfolded proteins routed to proteasome/macroautophagy pathways. | (pqac-00000006, pqac-00000011, pqac-00000015) |
| Non-canonical localization | Under stress, HSPA5/GRP78 can relocalize beyond the ER, including **cell surface**, and some reviews note presence in mitochondria/nucleus/secreted pools depending on context. | 2023 reviews summarize stress-induced relocalization and loss/saturation of ER retrieval control as one route to non-ER localization. | (pqac-00000008, pqac-00000010, pqac-00000013, pqac-00000015) |
| Cell-surface roles | **Cell-surface GRP78 (csGRP78)** acts as a signaling/attachment factor linked to cancer survival/therapy resistance and can serve as a **viral attachment/pro-viral factor**. It is being explored as a therapeutic target. | csGRP78 promotes PI3K/AKT-associated tumor phenotypes; antibody targeting suppresses tumor traits in preclinical models. Viral studies show GRP78 supports NDV attachment and that BiP inhibition blocks replication/spread of multiple dsDNA viruses. | (pqac-00000010, pqac-00000012, pqac-00000028, pqac-00000029, pqac-00000030) |


*Table: This table summarizes the core functional annotation of rat Hspa5/BiP/GRP78 (UniProt P06761), including identity, localization, molecular role, UPR regulation, proteostasis functions, and non-canonical cell-surface activities. It uses only claims supported by gathered evidence IDs for direct traceability.*