## ERP27
- **UniProt:** Q96DN0 · **batch:** proteostasis-batch-2026-06-07b · **review status:** COMPLETE
- **PN placement:** `ER proteostasis|Folding enzyme|Protein disulfide isomerases`. **PN-node mapping:** group `Protein disulfide isomerases`=mapped→**GO:0003756 protein disulfide isomerase activity** (new_to_goa); class `Folding enzyme`=no_mapping; branch=no_mapping.
- **Consistency:** **Direct contradiction.** Notes and review YAML both establish that ERP27 is a **catalytically inactive, non-catalytic PDI-family member that LACKS the CXXC active-site motif** and therefore cannot perform thiol-disulfide exchange. The review contains an explicit **negated** annotation — `GO:0003756 protein disulfide isomerase activity, negated: true` (IBA, GO_REF:0000033), action ACCEPT — i.e. the curated record states ERP27 does NOT have PDI activity. The PN group node projects the **exact same term GO:0003756 as new_to_goa** (a positive addition). PN proposes adding the precise term the review explicitly negates. This is the hardest conflict in the batch.
- **PN story / NEW pressure:** GO:0003756 (OLS-verified) must **NOT** be added to ERP27 — it is biologically wrong (no CXXC) and is already correctly captured as a NOT annotation in GOA/review. ERP27's real core functions are **GO:0051082 unfolded protein binding** (substrate discrimination via the b'-like cleft, PMID:23192347) and **GO:0051087 protein-folding chaperone binding** (recruits/presents substrates to the catalytic PDIA3/ERp57, PMID:16940051/23192347) — both added in the review, neither surfaced by the PN node. Conclusion: PN projection **over-reaches / is incorrect**; the review's substrate-presenter framing is the right model.
- **Mapping strategy:** This gene exposes the core flaw of the `Protein disulfide isomerases` group projecting GO:0003756 to all leaves: the node lumps catalytic isomerases (P4HB, AGR2-debated), redox oxidases (ERO1A/B), and **non-catalytic members (ERP27)**. For ERP27 the projection is not merely broad (TOMM20/HSPA8/RAB7A precedent) but actively wrong, contradicting an explicit negation. Gene-level mapping for ERP27 should be no_mapping for GO:0003756 (or carry the negation), with any positive mapping pointing at unfolded protein binding / chaperone-binding.
- **Evidence alignment:** PN dossier lists no reference titles. Review evidence (PMID:16940051 founding non-catalytic characterization, GOA-anchored to GO:0005788 EXP; PMID:23192347 crystal structure + ITC substrate discrimination) is reviewer-supplied and directly supports the non-catalytic substrate-presenter role. No shared citation list to compare; the biology flatly opposes the PN GO:0003756 projection.
- **Verdict:** **Contradiction** — PN projects GO:0003756 (new_to_goa) onto a gene whose review explicitly NEGATES that exact term (no CXXC, catalytically inactive). PN over-reaches; review is correct. **Recommended edits:** [MAP] remove/suppress the GO:0003756 projection for ERP27 (it is a non-catalytic PDI-family member; the term is correctly a NOT annotation). If a positive mapping is wanted, target GO:0051082 unfolded protein binding and/or GO:0051087 protein-folding chaperone binding (both OLS-real, both already in the review's core_functions).