## BAG2
- **UniProt:** O95816 · **batch:** proteostasis-batch-2026-06-06 · **review status:** COMPLETE
- **PN placement:** two rows — `Cytonuclear proteostasis|Chaperone|HSP70 system|HSP70 nucleotide exchange factor|BAG domain subtype` and `Ubiquitin Proteasome System|Proteasome and associated proteins|adaptors|BAG` ; **PN-node mapping:** NEF type → mapped/ok GO:0000774 (already_in_goa_exact); UPS adaptors group → mapped/ok GO:0070628 proteasome binding (new_to_goa); proteasome class → context_only/too_broad GO:0000502.
- **Consistency:** Row 1 fully consistent. Review, notes and Falcon deep research converge on BAG2 as an HSP70/HSC70 nucleotide-exchange factor (BAG domain) that inhibits CHIP/STUB1 E3 ligase and stabilizes clients (PMID:24318877, 16207813, 24383081, 25006867). GO:0000774 is the accepted core MF (verified real) and is ACCEPT in the review. Row 2 (proteasome adaptor → proteasome binding) is NOT supported: BAG2 acts on HSP70 and on the E3 CHIP, not on the 26S proteasome; neither review nor deep research reports direct proteasome binding. The tau pathway delivers tau "to the proteasome" but via HSP70, not by BAG2 binding the proteasome.
- **PN story / NEW pressure:** Row 1 already captured (GO:0000774 ACCEPT). Row 2 GO:0070628 proteasome binding (verified real term) is flagged new_to_goa, but it is an over-reach for BAG2 — no evidence BAG2 directly binds the proteasome. The better-supported UPS-side functions (ubiquitin protein ligase binding GO:0031625, negative regulation of ubiquitination GO:0031397) are already ACCEPT in the review. Conclusion: row 1 already captured; row 2 proteasome-binding projection over-reaches.
- **Mapping strategy:** Row-1 NEF mapping needs no change (exact match). Row-2 "proteasome binding" should NOT project onto BAG2; if the adaptors group genuinely shares proteasome binding, BAG2 is the exception (it is a chaperone/E3-adaptor, not a proteasome shuttle like the UBL-UBA family).
- **Evidence alignment:** PN cites no row-level references. Review/deep-research PMIDs (Arndt 2005=PMID:16207813, 24318877, 19228967, 24383081, 25006867) all concern HSP70/CHIP/client biology, none proteasome binding — divergent from the row-2 projection.
- **Verdict:** NEF classification sound and already captured; the UPS "adaptor → proteasome binding" projection is unsupported for BAG2. **Recommended edits:** [MAP] do not project GO:0070628 proteasome binding onto O95816 (BAG2 binds HSP70 and CHIP, not the proteasome); its UPS role is already covered by GO:0031625 / GO:0031397 in the review.