Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005789 endoplasmic reticulum membrane	IBA GO_REF:0000033	ACCEPT	Summary: ERO1B is a peripheral ER membrane protein on the lumenal side; this is its primary site of action, supported experimentally and by phylogenetic inference. Reason: The ER membrane (lumenal side) is the documented site where ERO1B reoxidizes PDI; corroborated by direct subcellular-location evidence. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0005783 endoplasmic reticulum	IEA GO_REF:0000002	ACCEPT	Summary: ER localization is correct and the principal compartment for ERO1B. Reason: ERO1B is an ER-resident oxidase; directly supported by immunofluorescence and glycosylation evidence. Supporting Evidence: PMID:10818100 the products of the ERO1-Lbeta gene are primarily localized in the ER of mammalian cells
GO:0005789 endoplasmic reticulum membrane	IEA GO_REF:0000044	ACCEPT	Summary: Electronic ER-membrane localization, consistent with experimental and IBA evidence. Reason: Correct compartment; ERO1B is a peripheral ER membrane protein. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Peripheral membrane protein
GO:0015035 protein-disulfide reductase activity	IEA GO_REF:0000120	MARK AS OVER ANNOTATED	Summary: This term asserts a disulfide REDUCTASE activity. ERO1B is mechanistically an OXIDASE that reoxidizes (forms disulfides in) PDI; the reductase label misrepresents the catalytic direction. Reason: ERO1B oxidizes PDI and passes electrons to O2 generating H2O2; the physiological direction is dithiol oxidation, not disulfide reduction, so a reductase annotation is an over-annotation. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Efficiently reoxidizes P4HB/PDI, the enzyme catalyzing protein disulfide formation, in order to allow P4HB to sustain additional rounds of disulfide formation.
GO:0016971 flavin-dependent sulfhydryl oxidase activity	IEA GO_REF:0000116	ACCEPT	Summary: This is the precise core molecular function of ERO1B - a FAD-dependent sulfhydryl oxidase catalyzing dithiol + O2 = disulfide + H2O2 (RHEA:59116). Reason: Matches the catalytic activity and FAD cofactor of ERO1B; supported by EXP evidence (PMID:11707400, PMID:21091435). Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Reaction=[protein]-dithiol + O2 = [protein]-disulfide + H2O2
GO:0016972 thiol oxidase activity	IEA GO_REF:0000120	ACCEPT	Summary: Thiol oxidase activity is the broader parent of ERO1B's flavin-dependent sulfhydryl oxidase activity; correct but less specific. Reason: Correctly captures ERO1B's oxidase activity; the EXP/IDA versions of the same term confirm it. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt EC=1.8.3.2
GO:0034975 protein folding in endoplasmic reticulum	IEA GO_REF:0000002	KEEP AS NON CORE	Summary: ERO1B drives oxidative protein folding in the ER; this is a valid downstream process outcome of its oxidase activity. Reason: Protein folding in the ER is the biological-process consequence of the oxidase activity rather than ERO1B's direct molecular function. Supporting Evidence: PMID:21091435 drives oxidative protein folding
GO:0071949 FAD binding	IEA GO_REF:0000002	ACCEPT	Summary: ERO1B is a flavoprotein that binds FAD as its cofactor. Reason: FAD is the documented cofactor (PMID:21091435), integral to the oxidase mechanism; FAD binding residues are mapped. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Name=FAD; Xref=ChEBI:CHEBI:57692
GO:0005515 protein binding	IPI PMID:20802462 Disulphide production by Ero1α-PDI relay is rapid and effect...	KEEP AS NON CORE	Summary: IntAct interaction with PDIA3/ERp57 (P30101). The bare protein binding term is uninformative; it records an interaction within the ER oxidoreductase network. Reason: Records a real physical interaction (PDIA3), but the generic protein binding term is uninformative and the informative function is the oxidase MF; ERO1B's principal PDI substrate is P4HB. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Q86YB8; P30101: PDIA3
GO:0005788 endoplasmic reticulum lumen	IEA GO_REF:0000107	ACCEPT	Summary: ERO1B acts on the lumenal side of the ER membrane; ER lumen is consistent with its site of action. Reason: ERO1B is a lumenal-side ER protein; ER lumen localization is consistent with its function. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Lumenal side
GO:0015036 disulfide oxidoreductase activity	IEA GO_REF:0000107	ACCEPT	Summary: A directionless parent term for thiol-disulfide oxidoreduction; correctly captures ERO1B's catalytic chemistry without mislabeling it as a reductase. Reason: Accurate (direction-neutral) molecular-function term for an enzyme that interconverts dithiols and disulfides on PDI; subsumed by the more specific sulfhydryl oxidase term. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Oxidoreductase involved in disulfide bond formation in the endoplasmic reticulum.
GO:0016020 membrane	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Generic membrane localization; ERO1B is a peripheral membrane protein, so this is consistent but uninformative. Reason: Correct but generic; the specific ER membrane term is preferred. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Peripheral membrane protein
GO:0030070 insulin processing	TAS Reactome:R-HSA-264876	KEEP AS NON CORE	Summary: ERO1B may drive oxidative proinsulin folding in pancreatic beta cells, contributing to insulin processing; a genuine but specialized, tissue-restricted role. Recent proteomic work corroborates ERO1B enrichment in beta cells and its association with insulin biogenesis. Reason: Supported as a plausible specialized function in pancreatic islets (where ERO1B is enriched), but it is a tissue-specific downstream role rather than the core oxidase function. The falcon deep research synthesizes recent proteomic data (axelsson2024) identifying ERO1B as enriched in pancreatic beta cells and implicated in insulin biogenesis, consistent with this annotation; this remains a specialized downstream process rather than the core MF. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt May be involved in oxidative proinsulin folding in pancreatic cells, hence may play a role in glucose homeostasis. file:human/ERO1B/ERO1B-deep-research-falcon.md ERO1B plays a specialized role in supporting the high protein secretory load of pancreatic beta cells, particularly for the folding and maturation of proinsulin file:human/ERO1B/ERO1B-deep-research-falcon.md Single-cell proteomics of human pancreatic islet cells found that ERO1B expression was higher in beta cells
GO:0016971 flavin-dependent sulfhydryl oxidase activity	EXP PMID:11707400 Manipulation of oxidative protein folding and PDI redox stat...	ACCEPT	Summary: Experimentally supported FAD-dependent sulfhydryl oxidase activity - ERO1B facilitates disulfide bond formation by oxidizing PDI. Reason: Direct experimental evidence (selective oxidation of PDI); core molecular function. Supporting Evidence: PMID:11707400 both human Ero1-Lalpha and Ero1-Lbeta (hEROs) facilitate disulfide bond formation in immunoglobulin subunits by selectively oxidizing PDI
GO:0016971 flavin-dependent sulfhydryl oxidase activity	EXP PMID:21091435 The endoplasmic reticulum sulfhydryl oxidase Ero1β drives ef...	ACCEPT	Summary: Experimentally supported FAD-dependent sulfhydryl oxidase activity; recombinant ERO1B is twice as active as ERO1A and oxidizes PDI efficiently. ERO1B acts on PDI (not client proteins directly) via a two-step ERO1-PDI relay. Reason: Direct enzymatic-assay evidence for the core oxidase function; ERO1B is a highly active, loosely regulated oxidase. The falcon deep research reinforces that ERO1B's catalytic substrate is reduced PDI, which it re-oxidizes so PDI can in turn introduce disulfide bonds into nascent secretory proteins. Supporting Evidence: PMID:21091435 recombinant human Ero1β is twice as active as Ero1α in enzymatic assays file:human/ERO1B/ERO1B-deep-research-falcon.md ERO1B does not directly oxidize client secretory proteins; instead, it functions in a two-step relay system
GO:0016972 thiol oxidase activity	EXP PMID:11707400 Manipulation of oxidative protein folding and PDI redox stat...	ACCEPT	Summary: Experimentally supported thiol oxidase activity (parent of the flavin-dependent sulfhydryl oxidase term). Reason: EXP evidence for oxidase activity; correct core function, though the flavin-dependent sulfhydryl oxidase term is the most precise. Supporting Evidence: PMID:11707400 both human Ero1-Lalpha and Ero1-Lbeta (hEROs) facilitate disulfide bond formation in immunoglobulin subunits by selectively oxidizing PDI
GO:0005788 endoplasmic reticulum lumen	TAS Reactome:R-HSA-9817575	ACCEPT	Summary: Reactome ER-lumen localization, consistent with ERO1B's lumenal-side site of action. Reason: Consistent with the documented lumenal-side ER localization. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Lumenal side
GO:0015035 protein-disulfide reductase activity	EXP PMID:11707400 Manipulation of oxidative protein folding and PDI redox stat...	MARK AS OVER ANNOTATED	Summary: This Reactome EXP annotation labels ERO1B as a protein-disulfide REDUCTASE. ERO1B physically engages PDI active-site disulfides, but its physiological action is oxidation of PDI (forming disulfides), not reduction; the reductase label is directionally misleading. Reason: The supporting study shows ERO1B/ERO1 oxidizes PDI; the reductase directionality mischaracterizes the enzyme, which is an oxidase. The accurate term is sulfhydryl oxidase / disulfide oxidoreductase activity. Supporting Evidence: PMID:11707400 both human Ero1-Lalpha and Ero1-Lbeta (hEROs) facilitate disulfide bond formation in immunoglobulin subunits by selectively oxidizing PDI
GO:0015035 protein-disulfide reductase activity	EXP PMID:16407158 Generating disulfides enzymatically: reaction products and e...	MARK AS OVER ANNOTATED	Summary: Reactome EXP reductase annotation. As above, the ERO1 enzyme generates disulfides (oxidase); the reductase directionality is misleading. Reason: The cited work concerns enzymatic disulfide generation by the ER thiol oxidase Ero1; an oxidase, not a reductase. The reductase term over-annotates the catalytic direction. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Following P4HB reoxidation, passes its electrons to molecular oxygen via FAD
GO:0015035 protein-disulfide reductase activity	EXP PMID:21091435 The endoplasmic reticulum sulfhydryl oxidase Ero1β drives ef...	MARK AS OVER ANNOTATED	Summary: Reactome EXP reductase annotation derived from the Ero1β characterization, which actually shows ERO1B oxidizes PDI; the reductase directionality is misleading. Reason: The supporting study demonstrates oxidase activity (oxidizing PDI), not disulfide reduction; the reductase term mislabels the catalytic direction. Supporting Evidence: PMID:21091435 Ero1β oxidizes PDI more efficiently than other PDI family members
GO:0034975 protein folding in endoplasmic reticulum	IDA PMID:21091435 The endoplasmic reticulum sulfhydryl oxidase Ero1β drives ef...	KEEP AS NON CORE	Summary: ERO1B drives oxidative protein folding in the ER; protein folding in the ER is a downstream process of its oxidase activity. Reason: A valid process annotation supported by direct evidence, but downstream of the core oxidase molecular function. Supporting Evidence: PMID:21091435 drives oxidative protein folding
GO:0016972 thiol oxidase activity	IDA PMID:21091435 The endoplasmic reticulum sulfhydryl oxidase Ero1β drives ef...	ACCEPT	Summary: Direct-assay thiol oxidase activity confirmed for recombinant ERO1B. Reason: IDA evidence for the core oxidase activity from enzymatic assays. Supporting Evidence: PMID:21091435 recombinant human Ero1β is twice as active as Ero1α in enzymatic assays
GO:0005783 endoplasmic reticulum	TAS PMID:10818100 Endoplasmic reticulum oxidoreductin 1-lbeta (ERO1-Lbeta), a ...	ACCEPT	Summary: ERO1-Lbeta is primarily localized in the ER (immunofluorescence, endoglycosidase sensitivity, in vitro translocation). Reason: TAS from the founding characterization directly establishes ER localization. Supporting Evidence: PMID:10818100 the products of the ERO1-Lbeta gene are primarily localized in the ER of mammalian cells
GO:0006457 protein folding	TAS PMID:10818100 Endoplasmic reticulum oxidoreductin 1-lbeta (ERO1-Lbeta), a ...	KEEP AS NON CORE	Summary: ERO1-Lbeta generates oxidative conditions in the ER required for disulfide bond formation; protein folding is the downstream process. Reason: A valid process annotation but downstream of the core oxidase molecular function. Supporting Evidence: PMID:10818100 ERO1-Lbeta is involved also in generating oxidative conditions in the ER
GO:0016491 oxidoreductase activity	NAS PMID:10818100 Endoplasmic reticulum oxidoreductin 1-lbeta (ERO1-Lbeta), a ...	ACCEPT	Summary: ERO1B is an oxidoreductase; a correct but very general parent term. Reason: Correct high-level molecular function, subsumed by the more specific flavin-dependent sulfhydryl oxidase activity. Supporting Evidence: file:human/ERO1B/ERO1B-uniprot.txt Oxidoreductase involved in disulfide bond formation in the endoplasmic reticulum.

Core Functions

FAD-dependent endoplasmic-reticulum sulfhydryl oxidase that reoxidizes the protein disulfide isomerase P4HB/PDI, regenerating PDI's active site to sustain disulfide-bond formation in secretory proteins, with electrons passed via FAD to O2 producing H2O2; intrinsically more active and more loosely regulated than ERO1A.

Molecular Function:

flavin-dependent sulfhydryl oxidase activity

Cellular Locations:

endoplasmic reticulum membrane endoplasmic reticulum lumen

Supporting Evidence:

file:human/ERO1B/ERO1B-uniprot.txt
Efficiently reoxidizes P4HB/PDI, the enzyme catalyzing protein disulfide formation, in order to allow P4HB to sustain additional rounds of disulfide formation.
PMID:21091435
recombinant human Ero1β is twice as active as Ero1α in enzymatic assays

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000044

Gene Ontology annotation based on UniProtKB Subcellular Location vocabulary mapping

GO_REF:0000107

Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara

GO_REF:0000116

Gene Ontology annotation based on RHEA mapping of reactions

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:10818100

Endoplasmic reticulum oxidoreductin 1-lbeta (ERO1-Lbeta), a human gene induced in the course of the unfolded protein response.

ERO1-Lbeta is a human EROs-family gene primarily localized to the ER, able to generate oxidative conditions in the ER (complementing the yeast ero1-1 mutant), with a distinct tissue distribution from ERO1-L and uniquely induced during the unfolded protein response.

PMID:11707400

Manipulation of oxidative protein folding and PDI redox state in mammalian cells.

Both human Ero1-Lalpha and Ero1-Lbeta facilitate disulfide bond formation in immunoglobulin subunits by selectively oxidizing PDI.

PMID:16407158

Generating disulfides enzymatically: reaction products and electron acceptors of the endoplasmic reticulum thiol oxidase Ero1p.

Characterizes the ER thiol oxidase Ero1 mechanism of enzymatic disulfide generation and electron acceptors (oxidase chemistry).

PMID:20802462

Disulphide production by Ero1α-PDI relay is rapid and effectively regulated.

PMID:21091435

The endoplasmic reticulum sulfhydryl oxidase Ero1β drives efficient oxidative protein folding with loose regulation.

Recombinant human Ero1β is twice as active as Ero1α, oxidizes PDI more efficiently than other PDI family members, drives oxidative protein folding preferentially via the a domain of PDI, and is loosely regulated (Cys130 critical for feedback); it is constitutively expressed in professional secretory tissues and UPR-induced.

Reactome:R-HSA-264876

Insulin processing

Reactome:R-HSA-9817575

Reactome ER-lumen oxidative folding annotation for ERO1B

file:human/ERO1B/ERO1B-uniprot.txt

UniProt entry Q86YB8 (ERO1B_HUMAN), ERO1-like protein beta

FAD-dependent ER sulfhydryl oxidase (EC 1.8.3.2) that reoxidizes P4HB/PDI (and other PDI-family members at lower rates) to drive disulfide-bond formation, passing electrons to O2 via FAD; peripheral lumenal-side ER membrane protein, homodimeric and heterodimeric with ERO1A; enriched in pancreatic islets and digestive tract; UPR-induced; implicated in proinsulin folding/glucose homeostasis.

file:human/ERO1B/ERO1B-deep-research-falcon.md

Falcon deep research report for ERO1B

Suggested Experiments

Experiment: Beta-cell-specific knockout or knockdown of ERO1B (alone and combined with ERO1A) followed by assays of proinsulin folding, insulin secretion and ER redox state to test its role in glucose homeostasis.

Experiment: Comparative enzymology of purified ERO1B versus ERO1A measuring O2 consumption, H2O2 production and PDI-isoform substrate preference, including the regulatory-disulfide mutants (e.g. Cys130) that govern feedback control.

Deep Research

Falcon

(ERO1B-deep-research-falcon.md)

Comprehensive Research Report: ERO1B (Endoplasmic Reticulum Oxidoreductase 1 Beta) Falcon Edison Scientific Literature 21 citations 1 artifacts 2026-06-20T06:21:39.854338

Edison artifact artifact-00 (text/markdown)

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

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Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Comprehensive Research Report: ERO1B (Endoplasmic Reticulum Oxidoreductase 1 Beta)

Gene and Protein Identity

ERO1B (Gene ID: ERO1B, UniProt: Q86YB8) encodes ERO1-like protein beta, also known as endoplasmic reticulum oxidoreductin-1-like protein B or oxidoreductin-1-L-beta, in Homo sapiens (varone2025smallmoleculemediatedinhibition pages 1-2). The protein is classified as EC 1.8.3.2 and belongs to the evolutionarily conserved ERO1 family of flavin adenine dinucleotide (FAD)-containing sulfhydryl oxidases (zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6). ERO1B shares approximately 65% amino acid sequence identity with its paralogue ERO1A, and the two proteins have overlapping but distinct expression patterns and functions (varone2025smallmoleculemediatedinhibition pages 1-2).

Primary Molecular Function and Enzymatic Activity

Core Enzymatic Function

ERO1B functions as a protein disulfide oxidase that catalyzes a critical step in oxidative protein folding within the endoplasmic reticulum (ER) (zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6). The enzyme operates through a FAD-dependent mechanism to introduce disulfide bonds into nascent secretory and membrane proteins (zito2015ero1aprotein pages 1-6, benham2013ero1–pdiinteractionsthe pages 1-3).

Catalyzed Reaction

The fundamental reaction catalyzed by ERO1B involves the transfer of electrons from reduced protein disulfide isomerase (PDI) to molecular oxygen, producing hydrogen peroxide as a byproduct (zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6, frand1999ero1poxidizesprotein pages 1-2). The stoichiometric reaction can be represented as:

O₂ + 2H⁺ + 2e⁻ → H₂O₂

For each disulfide bond formed, one molecule of H₂O₂ is generated, making ERO1B both a protein folding catalyst and a significant source of reactive oxygen species (ROS) in the ER (zito2015ero1aprotein pages 1-6, bhattarai2021theaftermathof pages 1-2).

Substrate Specificity

The primary and best-characterized substrate of ERO1B is protein disulfide isomerase (PDI), particularly the PDI family of oxidoreductases (frand1999ero1poxidizesprotein pages 1-2, benham2013ero1–pdiinteractionsthe pages 1-3, zhang2014differentinteractionmodes pages 1-2). ERO1B does not directly oxidize client secretory proteins; instead, it functions in a two-step relay system (benham2013ero1–pdiinteractionsthe pages 1-3):

ERO1B oxidizes reduced PDI, restoring PDI to its oxidized, active state
Oxidized PDI then directly catalyzes disulfide bond formation in nascent secretory proteins

Studies of the ERO1-PDI interaction have revealed specific mechanistic details. The ERO1 protein contains an outer active site with a -CXXXXC- motif that accepts electrons from PDI's active sites, which are then transferred to an inner -CXXC- active site before being passed to the FAD cofactor and ultimately to molecular oxygen (zito2024fingerprintofthe pages 1-3, zhang2014differentinteractionmodes pages 1-2). In mammalian systems, ERO1 proteins preferentially oxidize the C-terminal active site (a' domain) of PDI rather than the N-terminal active site (a domain), though both can serve as substrates (zhang2014differentinteractionmodes pages 1-2).

Multiple PDI family members can serve as substrates for ERO1, including PDI (PDIA1), Mpd1p, Mpd2p, ERp46, ERp57, ERp72, and others, though with varying efficiency (vitu2010oxidativeactivityof pages 1-2). The amino-terminal domain of PDI was found to be oxidized most rapidly by yeast Ero1p compared to other oxidoreductase active sites (vitu2010oxidativeactivityof pages 1-2).

Subcellular Localization

ERO1B is localized exclusively to the endoplasmic reticulum (ER) lumen, where it carries out its oxidative protein folding function (varone2025smallmoleculemediatedinhibition pages 1-2, zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6). The protein contains an N-terminal signal sequence that directs it to the ER during translation, and it is retained within this compartment as an ER-resident oxidoreductase (bhattarai2021theaftermathof pages 1-2). This localization is essential for its role in the folding of secretory pathway proteins, which enter the ER in an unfolded state and must acquire proper disulfide bonds before export to the Golgi apparatus (szarka2011oxidativefoldingrecent pages 1-2, benham2013ero1–pdiinteractionsthe pages 1-3).

Signaling and Biochemical Pathways

Oxidative Protein Folding Pathway

ERO1B participates in the core oxidative protein folding pathway in the ER, functioning as part of the ERO1-PDI relay system (zito2024fingerprintofthe pages 1-3, szarka2011oxidativefoldingrecent pages 1-2, benham2013ero1–pdiinteractionsthe pages 1-3). This pathway is fundamental to ER proteostasis, ensuring that secretory and membrane proteins acquire their proper disulfide bond configurations. The pathway operates as follows:

Nascent proteins with free cysteine residues enter the ER lumen
PDI catalyzes disulfide bond formation in these proteins, becoming reduced in the process
ERO1B re-oxidizes reduced PDI, transferring electrons to oxygen
This regenerates oxidized PDI for additional rounds of substrate protein oxidation

Regulation by Redox-Dependent Mechanisms

ERO1B activity is tightly regulated through regulatory disulfide bonds that act as molecular switches, modulating enzyme activity based on the redox state of the ER (zito2015ero1aprotein pages 1-6, moilanen2020nonnativeproteinsinhibit pages 1-2, zhang2014differentinteractionmodes pages 1-2). In mammalian ERO1α (and by extension, ERO1B, given their structural similarity), regulatory disulfides between catalytic and non-catalytic cysteines (e.g., Cys94-Cys131 and Cys99-Cys104) control access to the active site (zhang2014differentinteractionmodes pages 1-2). Under oxidizing conditions, these regulatory disulfides form and inactivate ERO1, preventing hyperoxidation of the ER. Under more reducing conditions (such as during high protein folding demand), these regulatory disulfides are reduced by PDI, activating ERO1 for sustained oxidative activity (zito2015ero1aprotein pages 1-6, zhang2014differentinteractionmodes pages 1-2).

This creates a feedback regulation mechanism where PDI serves both as substrate and regulator of ERO1 activity (benham2013ero1–pdiinteractionsthe pages 1-3, moilanen2020nonnativeproteinsinhibit pages 1-2, zhang2014differentinteractionmodes pages 1-2). When non-native protein load exceeds the folding capacity of the ER, the ERO1-PDI relay can be inhibited by feedback mechanisms involving unfolded proteins and folding intermediates, allowing client proteins to remain in a reduced state and minimizing futile oxidation-reduction cycles (moilanen2020nonnativeproteinsinhibit pages 1-2).

Unfolded Protein Response (UPR) and ER Stress

ERO1B is integrated with the unfolded protein response (UPR), a homeostatic signaling pathway activated when ER protein folding capacity is overwhelmed (zito2015ero1aprotein pages 1-6, bhattarai2021theaftermathof pages 1-2, moilanen2020nonnativeproteinsinhibit pages 1-2). The UPR upregulates ER chaperones, folding catalysts including ERO1 proteins, and ER-associated degradation (ERAD) components to restore ER homeostasis (bhattarai2021theaftermathof pages 1-2). ERO1 activity must be balanced with protein folding demand, and excessive ERO1 activity during severe ER stress can contribute to oxidative stress and potentially shift from an adaptive to a maladaptive UPR response (zito2015ero1aprotein pages 1-6, bhattarai2021theaftermathof pages 1-2).

Redox Homeostasis and ROS Production

Because ERO1B couples disulfide bond formation to the reduction of molecular oxygen, it is a significant producer of H₂O₂ in the ER lumen (zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6, bhattarai2021theaftermathof pages 1-2). It has been estimated that ERO1 activity accounts for approximately 25% of H₂O₂ produced during protein translation (zito2024fingerprintofthe pages 1-3). This positions ERO1B at the intersection of protein folding and redox signaling, contributing to both ER proteostasis and oxidative stress (zito2015ero1aprotein pages 1-6, bhattarai2021theaftermathof pages 1-2).

Functional Redundancy with Alternative Oxidases

Unlike in yeast, where ERO1 is essential for viability, mammalian cells can survive without ERO1 proteins due to functional compensation by alternative ER oxidases, particularly peroxiredoxin 4 (PRDX4), glutathione peroxidase 7 (GPX7), and glutathione peroxidase 8 (GPX8) (varone2025smallmoleculemediatedinhibition pages 1-2, zito2024fingerprintofthe pages 1-3, konno2015ero1independentproductionof pages 1-2). Mice lacking both ERO1α and ERO1β are viable and fertile, though they exhibit delayed disulfide bond formation and subtle functional defects (zito2024fingerprintofthe pages 1-3). PRDX4, which also uses H₂O₂ as an electron acceptor, can support disulfide bond formation in ERO1-deficient cells (konno2015ero1independentproductionof pages 1-2). The sequential action of ERO1 and PRDX4 can produce two disulfides from every molecule of oxygen converted to water (konno2015ero1independentproductionof pages 1-2).

Biological Processes and Physiological Roles

Tissue-Specific Expression

While ERO1A is ubiquitously expressed, ERO1B shows preferential expression in secretory tissues, most notably in the pancreas and pancreatic islet beta cells (axelsson2024proteomicassociationswith pages 2-4, varone2025smallmoleculemediatedinhibition pages 1-2). This tissue-specific expression pattern suggests that ERO1B is particularly important for cells with high secretory demands, where large quantities of disulfide-containing proteins must be efficiently folded and secreted (axelsson2024proteomicassociationswith pages 2-4).

Role in Pancreatic Beta Cell Function and Insulin Biogenesis

Recent proteomic studies have implicated ERO1B in insulin biogenesis and pancreatic islet function (axelsson2024proteomicassociationswith pages 2-4). A 2024 study analyzing Rap1A GTPase signaling-deficient mouse pancreata identified ERO1-like protein β (Ero1lβ) as one of the proteins exclusively involved in insulin biogenesis, with roles in insulin metabolism (axelsson2024proteomicassociationswith pages 2-4). The mRNA expression of Ero1lβ was significantly increased in Rap1A-deficient pancreata compared to wild-type, and functional enrichment analysis showed involvement in protein secretion pathways (axelsson2024proteomicassociationswith pages 2-4). Single-cell proteomics of human pancreatic islet cells found that ERO1B expression was higher in beta cells, along with other proteins involved in Ca²⁺ homeostasis and secretory function (axelsson2024proteomicassociationswith pages 2-4).

These findings suggest that ERO1B plays a specialized role in supporting the high protein secretory load of pancreatic beta cells, particularly for the folding and maturation of proinsulin and other disulfide-rich secretory proteins.

Association with Respiratory Function

A 2024 Mendelian randomization study identified circulating ERO1B as causally associated with forced expiratory volume (FEV1), a key measure of lung function (axelsson2024proteomicassociationswith pages 2-4). The study found that ERO1B was among three proteins (along with THBS2 and APOM) showing directionally consistent associations between observational and MR analyses for FEV1 (axelsson2024proteomicassociationswith pages 2-4). While the mechanistic basis for this association is not yet fully elucidated, it suggests that ERO1B may play a role in respiratory physiology, potentially through its involvement in the secretion of proteins important for lung function.

Protein Secretion and ER Proteostasis

ERO1B contributes to protein secretion pathways in specialized secretory cells (axelsson2024proteomicassociationswith pages 2-4, voronkova2024ero1alevelsare pages 1-2). Studies have shown that genes involved in vesicle transport from the ER to Golgi, including components of the coatomer complex (COPB2, COPB1, COPE) and RAB5A, show increased expression in high ERO1A-expressing contexts, suggesting coordination between oxidative folding and secretory trafficking (voronkova2024ero1alevelsare pages 1-2). By extension, ERO1B likely plays a similar role in secretory tissues where it is highly expressed.

Evolutionary and Structural Context

ERO1B belongs to the ERO1 family, which is evolutionarily conserved across eukaryotes (zito2024fingerprintofthe pages 1-3, szarka2011oxidativefoldingrecent pages 1-2). However, the essentiality of ERO1 varies across species. In Saccharomyces cerevisiae, ERO1 is essential for viability, and conditional ero1-1 mutants accumulate reduced secretory proteins in the ER and are highly sensitive to reducing agents (frand1999ero1poxidizesprotein pages 1-2). In contrast, mammalian ERO1 proteins are dispensable under normal conditions due to compensatory oxidative systems (varone2025smallmoleculemediatedinhibition pages 1-2, zito2024fingerprintofthe pages 1-3).

The domain architecture of ERO1 proteins includes conserved cysteine residues organized into inner and outer active sites, as well as regulatory cysteines that control enzyme activity (zito2024fingerprintofthe pages 1-3, zhang2014differentinteractionmodes pages 1-2). The FAD cofactor is essential for the electron transfer reaction that ultimately reduces molecular oxygen (zito2015ero1aprotein pages 1-6).

Recent Developments and Current Understanding (2023-2025)

Recent Clinical and Physiological Studies

Recent studies from 2024-2025 have expanded our understanding of ERO1B's physiological roles:

Pancreatic islet function: ERO1B was identified as a key protein involved in insulin biogenesis in proteomic analyses of Rap1A-deficient pancreata (2024) (axelsson2024proteomicassociationswith pages 2-4)
Respiratory physiology: Proteomic associations with forced expiratory volume established ERO1B as a potential causal factor in lung function through Mendelian randomization (2024) (axelsson2024proteomicassociationswith pages 2-4)
Single-cell proteomics: Single-cell proteomic analysis of pancreatic islets revealed ERO1B enrichment in beta cells and its association with type 1 diabetes-related changes (2025) (axelsson2024proteomicassociationswith pages 2-4)

Understanding of Redundancy and Compensation

The field has consolidated understanding that while ERO1 proteins are important for optimal ER function, they are not absolutely essential in mammals due to compensation by PRDX4 and glutathione peroxidases (varone2025smallmoleculemediatedinhibition pages 1-2, zito2024fingerprintofthe pages 1-3, konno2015ero1independentproductionof pages 1-2). This has been demonstrated through knockout studies showing that mice lacking both ERO1α and ERO1β remain viable (zito2024fingerprintofthe pages 1-3). However, the ERO1-PRDX4 system becomes critical under conditions of high secretory demand or ER stress (konno2015ero1independentproductionof pages 1-2).

Regulation and Feedback Mechanisms

Recent mechanistic studies have clarified the complex regulatory networks governing ERO1 activity (moilanen2020nonnativeproteinsinhibit pages 1-2, zhang2014differentinteractionmodes pages 1-2). The discovery that non-native proteins can inhibit the ERO1-PDI relay when protein folding capacity is exceeded reveals a feedback inhibition mechanism that prevents futile oxidation-reduction cycles and may enhance ERAD of misfolded proteins (moilanen2020nonnativeproteinsinhibit pages 1-2). This regulatory cross-talk between oxidative protein folding and the UPR/ERAD pathways represents an important advance in understanding ER homeostasis.

Summary Table

Feature	ERO1B summary	Evidence
Verified identity	Human ERO1B encodes ERO1-like protein beta / endoplasmic reticulum oxidoreductase 1 beta, an ERO1-family sulfhydryl oxidase distinct from ERO1A but closely related to it.	(voronkova2024ero1alevelsare pages 1-2, varone2025smallmoleculemediatedinhibition pages 1-2, zito2024fingerprintofthe pages 1-3)
Enzymatic class and cofactor	ERO1-family proteins are FAD-containing protein disulfide oxidases that drive oxidative protein folding in the ER. ERO1B is annotated as EC 1.8.3.2 and is inferred to use the same core catalytic chemistry as mammalian ERO1A.	(voronkova2024ero1alevelsare pages 1-2, zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6)
Reaction catalyzed	ERO1 proteins transfer oxidizing equivalents from the enzyme to PDI, while ultimately transferring electrons to molecular oxygen, which is reduced to H2O2. Net effect: regeneration of oxidized PDI for disulfide-bond formation in secretory proteins, coupled to peroxide production.	(zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6, benham2013ero1–pdiinteractionsthe pages 1-3)
Primary substrate specificity	The best-supported direct substrate is protein disulfide isomerase (PDI/PDIA1) and related PDI-family oxidoreductases rather than mature secretory proteins directly. Secretory and membrane proteins are the downstream client substrates oxidized indirectly through the ERO1–PDI relay.	(frand1999ero1poxidizesprotein pages 1-2, benham2013ero1–pdiinteractionsthe pages 1-3, zhang2014differentinteractionmodes pages 1-2, vitu2010oxidativeactivityof pages 1-2)
Biochemical role in oxidative folding	ERO1B functions in the ER oxidative folding relay, restoring oxidized PDI so PDI can introduce and rearrange disulfide bonds in nascent secretory-pathway proteins. This places ERO1B in the core machinery for ER proteostasis.	(zito2024fingerprintofthe pages 1-3, szarka2011oxidativefoldingrecent pages 1-2, zito2015ero1aprotein pages 1-6, benham2013ero1–pdiinteractionsthe pages 1-3)
Subcellular localization	ERO1-family proteins are ER-localized/ER-resident oxidoreductases acting in the ER lumen on the folding of secretory and membrane proteins. For ERO1B, this localization is consistent with its signal peptide and role in ER oxidative folding.	(voronkova2024ero1alevelsare pages 1-2, zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6, bhattarai2021theaftermathof pages 1-2)
Regulatory mechanisms	Mammalian ERO1 activity is controlled by intramolecular regulatory disulfides that switch the enzyme between more active and less active states depending on ER redox conditions. PDI both serves as substrate and helps regulate ERO1 activity, creating feedback control that limits hyperoxidation.	(zito2015ero1aprotein pages 1-6, moilanen2020nonnativeproteinsinhibit pages 1-2, zhang2014differentinteractionmodes pages 1-2)
Coupling to ROS/redox homeostasis	Because oxygen is the terminal electron acceptor, ERO1 activity generates stoichiometric H2O2, linking disulfide production to ER redox tone and oxidative stress signaling. ERO1 therefore contributes both to protein folding and to ER ROS burden.	(zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6, bhattarai2021theaftermathof pages 1-2, konno2015ero1independentproductionof pages 1-2)
Relationship to unfolded protein response (UPR)	ERO1-family activity is integrated with ER stress responses/UPR: oxidative folding capacity must match client-protein load, and excessive non-native protein load can inhibit the ERO1–PDI relay. ERO1 expression/activity is therefore part of adaptive ER proteostasis control.	(zito2015ero1aprotein pages 1-6, bhattarai2021theaftermathof pages 1-2, moilanen2020nonnativeproteinsinhibit pages 1-2)
Biological pathways	Key pathways include oxidative protein folding, ER proteostasis, protein secretion, disulfide-bond formation, ER stress/UPR, and redox homeostasis.	(zito2024fingerprintofthe pages 1-3, szarka2011oxidativefoldingrecent pages 1-2, benham2013ero1–pdiinteractionsthe pages 1-3, bhattarai2021theaftermathof pages 1-2)
Relationship to ERO1A	ERO1B is the paralogue of ERO1A; the two mammalian proteins share substantial sequence identity and overlapping function. ERO1A is broadly expressed, whereas ERO1B is more enriched in specialized secretory settings.	(varone2025smallmoleculemediatedinhibition pages 1-2, zhang2014differentinteractionmodes pages 1-2)
Tissue-expression pattern	Available evidence indicates ERO1A is ubiquitous, whereas ERO1B is enriched in secretory tissues, especially the pancreas/islet beta-cell context. Recent proteomic studies detected ERO1B in pancreatic-islet datasets and linked it to insulin-secretory biology.	(axelsson2024proteomicassociationswith pages 2-4, varone2025smallmoleculemediatedinhibition pages 1-2)
Physiological roles	ERO1B is most plausibly specialized for high secretory demand, supporting maturation of disulfide-rich proteins in endocrine/exocrine cells. Human and mouse studies associate ERO1B with insulin biogenesis/islet function and with broader secretory proteostasis.	(axelsson2024proteomicassociationswith pages 2-4, varone2025smallmoleculemediatedinhibition pages 1-2)
Real-world/clinical associations	Recent human proteogenomic work associated circulating ERO1B measurements with FEV1/lung function and supported a potentially causal relationship in Mendelian-randomization analyses, though this does not yet define mechanism.	(axelsson2024proteomicassociationswith pages 2-4)
Functional redundancy with other oxidases	In mammals, ERO1 loss is not absolutely essential because alternative ER oxidizing systems can compensate, notably PRDX4 and GPX7/GPX8. Combined ERO1A/ERO1B loss causes delayed disulfide formation but relatively mild organismal phenotypes compared with yeast ERO1 deficiency.	(voronkova2024ero1alevelsare pages 1-2, varone2025smallmoleculemediatedinhibition pages 1-2, zito2024fingerprintofthe pages 1-3, konno2015ero1independentproductionof pages 1-2)
Evidence strength/limitations	Direct mechanistic literature on human ERO1B specifically is limited compared with ERO1A; many functional inferences rely on conserved ERO1-family biochemistry plus expression/physiology studies showing ERO1B enrichment in secretory tissues.	(voronkova2024ero1alevelsare pages 1-2, zito2024fingerprintofthe pages 1-3, zito2015ero1aprotein pages 1-6)

Table: This table consolidates the key functional characteristics of human ERO1B, including its enzymatic role, localization, regulation, pathway context, tissue expression, and redundancy with related oxidases. It is useful as a compact evidence-backed reference for gene functional annotation.

Conclusions

ERO1B (ERO1-like protein beta) is a FAD-containing sulfhydryl oxidase localized to the ER lumen, where it catalyzes a key step in oxidative protein folding by oxidizing PDI family proteins. The enzyme transfers electrons from reduced PDI to molecular oxygen, producing H₂O₂ as a byproduct. ERO1B functions within the oxidative protein folding pathway and is integrated with the UPR and ER stress response mechanisms. Its activity is regulated by redox-dependent formation of regulatory disulfide bonds, which provide feedback control to prevent ER hyperoxidation.

While ERO1B shares substantial functional overlap with ERO1A (approximately 65% sequence identity), it shows preferential expression in secretory tissues, particularly the pancreas, where it contributes to insulin biogenesis and secretory cell function. Unlike yeast ERO1, mammalian ERO1 proteins including ERO1B are not absolutely essential due to functional compensation by alternative oxidases such as PRDX4 and glutathione peroxidases.

Recent studies (2023-2025) have expanded understanding of ERO1B's physiological roles, identifying associations with pancreatic islet function, insulin secretion, and lung function. The protein represents an important component of ER proteostasis machinery in specialized secretory cells, balancing the demands of high protein secretion with the need to maintain proper redox homeostasis in the ER.

References

(varone2025smallmoleculemediatedinhibition pages 1-2): Ersilia Varone, Michele Retini, Alessandro Cherubini, Alexander Chernorudskiy, Alice Marrazza, Andrea Guidarelli, Alfredo Cagnotto, Marten Beeg, Marco Gobbi, Stefano Fumagalli, Marco Bolis, Luca Guarrera, Maria Chiara Barbera, Chiara Grasselli, Augusto Bleve, Daniele Generali, Manuela Milani, Michele Mari, Mario Salmona, Giovanni Piersanti, Giovanni Bottegoni, Massimo Broggini, Yvonne M. W. Janssen-Heininger, Jaehyung Cho, Orazio Cantoni, and Ester Zito. Small molecule-mediated inhibition of the oxidoreductase ero1a restrains aggressive breast cancer by impairing vegf and pd-l1 in the tumor microenvironment. Cell Death & Disease, Feb 2025. URL: https://doi.org/10.1038/s41419-025-07426-1, doi:10.1038/s41419-025-07426-1. This article has 16 citations and is from a peer-reviewed journal.
(zito2024fingerprintofthe pages 1-3): Ester Zito, Luca Guarrera, and Yvonne M.W. Janssen-Heininger. Fingerprint of the oxido-reductase ero1: a protein disulfide bond producer and supporter of cancer. Jan 2024. URL: https://doi.org/10.1016/j.bbcan.2023.189027, doi:10.1016/j.bbcan.2023.189027. This article has 27 citations and is from a peer-reviewed journal.
(zito2015ero1aprotein pages 1-6): Ester Zito. Ero1: a protein disulfide oxidase and h2o2 producer. Free radical biology & medicine, 83:299-304, Jun 2015. URL: https://doi.org/10.1016/j.freeradbiomed.2015.01.011, doi:10.1016/j.freeradbiomed.2015.01.011. This article has 216 citations and is from a peer-reviewed journal.
(benham2013ero1–pdiinteractionsthe pages 1-3): Adam M. Benham, Marcel van Lith, Roberto Sitia, and Ineke Braakman. Ero1–pdi interactions, the response to redox flux and the implications for disulfide bond formation in the mammalian endoplasmic reticulum. Philosophical Transactions of the Royal Society B: Biological Sciences, 368:20110403, May 2013. URL: https://doi.org/10.1098/rstb.2011.0403, doi:10.1098/rstb.2011.0403. This article has 107 citations and is from a domain leading peer-reviewed journal.
(frand1999ero1poxidizesprotein pages 1-2): Alison R Frand and Chris A Kaiser. Ero1p oxidizes protein disulfide isomerase in a pathway for disulfide bond formation in the endoplasmic reticulum. Molecular cell, 4 4:469-77, Oct 1999. URL: https://doi.org/10.1016/s1097-2765(00)80198-7, doi:10.1016/s1097-2765(00)80198-7. This article has 499 citations and is from a highest quality peer-reviewed journal.
(bhattarai2021theaftermathof pages 1-2): Kashi Raj Bhattarai, Thoufiqul Alam Riaz, Hyung-Ryong Kim, and Han-Jung Chae. The aftermath of the interplay between the endoplasmic reticulum stress response and redox signaling. Experimental & Molecular Medicine, 53:151-167, Feb 2021. URL: https://doi.org/10.1038/s12276-021-00560-8, doi:10.1038/s12276-021-00560-8. This article has 393 citations and is from a peer-reviewed journal.
(zhang2014differentinteractionmodes pages 1-2): Lihui Zhang, Yingbo Niu, Li Zhu, Jingqi Fang, Xi'e Wang, Lei Wang, and Chih-chen Wang. Different interaction modes for protein-disulfide isomerase (pdi) as an efficient regulator and a specific substrate of endoplasmic reticulum oxidoreductin-1α (ero1α). Journal of Biological Chemistry, 289:31188-31199, Nov 2014. URL: https://doi.org/10.1074/jbc.m114.602961, doi:10.1074/jbc.m114.602961. This article has 70 citations and is from a domain leading peer-reviewed journal.
(vitu2010oxidativeactivityof pages 1-2): Elvira Vitu, Sunghwan Kim, Carolyn S. Sevier, Omer Lutzky, Nimrod Heldman, Moran Bentzur, Tamar Unger, Meital Yona, Chris A. Kaiser, and Deborah Fass. Oxidative activity of yeast ero1p on protein disulfide isomerase and related oxidoreductases of the endoplasmic reticulum. Journal of Biological Chemistry, 285:18155-18165, Jun 2010. URL: https://doi.org/10.1074/jbc.m109.064931, doi:10.1074/jbc.m109.064931. This article has 57 citations and is from a domain leading peer-reviewed journal.
(szarka2011oxidativefoldingrecent pages 1-2): András Szarka and Gábor Bánhegyi. Oxidative folding: recent developments. BioMolecular Concepts, 2:379-390, Oct 2011. URL: https://doi.org/10.1515/bmc.2011.038, doi:10.1515/bmc.2011.038. This article has 6 citations and is from a peer-reviewed journal.
(moilanen2020nonnativeproteinsinhibit pages 1-2): Antti Moilanen and Lloyd W. Ruddock. Non-native proteins inhibit the er oxidoreductin 1 (ero1)–protein disulfide-isomerase relay when protein folding capacity is exceeded. Journal of Biological Chemistry, 295:8647-8655, Jun 2020. URL: https://doi.org/10.1074/jbc.ra119.011766, doi:10.1074/jbc.ra119.011766. This article has 17 citations and is from a domain leading peer-reviewed journal.
(konno2015ero1independentproductionof pages 1-2): Tasuku Konno, Eduardo Pinho Melo, Carlos Lopes, Ilir Mehmeti, Sigurd Lenzen, David Ron, and Edward Avezov. Ero1-independent production of h2o2 within the endoplasmic reticulum fuels prdx4-mediated oxidative protein folding. The Journal of Cell Biology, 211:253-259, Oct 2015. URL: https://doi.org/10.1083/jcb.201506123, doi:10.1083/jcb.201506123. This article has 84 citations.
(axelsson2024proteomicassociationswith pages 2-4): Gisli Thor Axelsson, Thorarinn Jonmundsson, Youngjae Woo, Elisabet Alexandra Frick, Thor Aspelund, Joseph J. Loureiro, Anthony P. Orth, Lori L. Jennings, Gunnar Gudmundsson, Valur Emilsson, Valborg Gudmundsdottir, and Vilmundur Gudnason. Proteomic associations with forced expiratory volume: a mendelian randomisation study. Respiratory Research, Jan 2024. URL: https://doi.org/10.1186/s12931-023-02587-z, doi:10.1186/s12931-023-02587-z. This article has 7 citations and is from a domain leading peer-reviewed journal.
(voronkova2024ero1alevelsare pages 1-2): M. A. Voronkova, B. Johnson, N. Gandhi, J. M. Koomen, M Patrick, S. Shanthi Bhupathi, V. M. Wu, A. Elliott, A. Vanderwalde, B. Halmos, and L. A. Hazlehurst. Ero1a levels are a prognostic indicator in egfr mutated non small cell lung cancer. NPJ Precision Oncology, Nov 2024. URL: https://doi.org/10.1038/s41698-024-00736-1, doi:10.1038/s41698-024-00736-1. This article has 9 citations and is from a peer-reviewed journal.

Artifacts

Edison artifact artifact-00

Citations

varone2025smallmoleculemediatedinhibition pages 1-2
zhang2014differentinteractionmodes pages 1-2
vitu2010oxidativeactivityof pages 1-2
bhattarai2021theaftermathof pages 1-2
moilanen2020nonnativeproteinsinhibit pages 1-2
zito2024fingerprintofthe pages 1-3
axelsson2024proteomicassociationswith pages 2-4
szarka2011oxidativefoldingrecent pages 1-2
https://doi.org/10.1038/s41419-025-07426-1,
https://doi.org/10.1016/j.bbcan.2023.189027,
https://doi.org/10.1016/j.freeradbiomed.2015.01.011,
https://doi.org/10.1098/rstb.2011.0403,
https://doi.org/10.1016/s1097-2765(00
https://doi.org/10.1038/s12276-021-00560-8,
https://doi.org/10.1074/jbc.m114.602961,
https://doi.org/10.1074/jbc.m109.064931,
https://doi.org/10.1515/bmc.2011.038,
https://doi.org/10.1074/jbc.ra119.011766,
https://doi.org/10.1083/jcb.201506123,
https://doi.org/10.1186/s12931-023-02587-z,
https://doi.org/10.1038/s41698-024-00736-1,

📚 Additional Documentation

Notes

(ERO1B-notes.md)

ERO1B (ERO1LB, ERO1-Lbeta) research notes

UniProt Q86YB8. ER oxidoreductin-1 beta; FAD-dependent sulfhydryl oxidase (EC 1.8.3.2), paralog of ERO1A.

Core molecular function

Reoxidizes P4HB/PDI to drive disulfide-bond formation; passes electrons to O2 via FAD producing H2O2.
[file:human/ERO1B/ERO1B-uniprot.txt "Oxidoreductase involved in disulfide bond formation in the endoplasmic reticulum. Efficiently reoxidizes P4HB/PDI..."]
More active than ERO1A, looser regulation: PMID:21091435
FAD cofactor (PMID:21091435); 7 FAD binding residues mapped by similarity to ERO1A.
Redox-active center Cys90/Cys95 and Cys393/Cys396. Long-range regulatory disulfides; Cys130 critical for feedback.

Tissue / biology

Enriched in professional secretory tissues, esp pancreas (islets of Langerhans), digestive tract, stomach chief cells.
[file "In the pancreas, expressed in islets of Langerhans"]
May function in oxidative proinsulin folding -> glucose homeostasis: [file "May be involved in oxidative proinsulin folding in pancreatic cells, hence may play a role in glucose homeostasis."]
Induced by UPR: PMID:10818100
Primarily ER-localized: PMID:10818100
Homodimer (disulfide-linked); heterodimer with ERO1A.

Action plan

Core MF: flavin-dependent sulfhydryl oxidase activity (GO:0016971) EXP - ACCEPT.
thiol oxidase activity (GO:0016972) EXP/IDA - ACCEPT (parent).
protein-disulfide reductase activity (GO:0015035) EXP (Reactome) x3 + IEA: ERO1 is an oxidase not reductase. The "reductase" label mislabels directionality. The physical engagement of PDI disulfides is real but the term direction is wrong -> MARK_AS_OVER_ANNOTATED.
disulfide oxidoreductase activity (GO:0015036) IEA - ACCEPT (correct directionless parent).
oxidoreductase activity (GO:0016491) NAS - ACCEPT general.
FAD binding (GO:0071949) - ACCEPT.
protein binding (PMID:20802462, PDIA3 P30101) - KEEP_AS_NON_CORE.
ER / ER membrane / ER lumen / membrane localizations - ACCEPT (ER), KEEP_AS_NON_CORE (generic membrane).
protein folding / protein folding in ER - KEEP_AS_NON_CORE (downstream BP).
insulin processing (GO:0030070) TAS Reactome - KEEP_AS_NON_CORE (genuine specialized role in pancreas, proinsulin folding).

Pn Notes

(ERO1B-pn-notes.md)

ERO1B PN Consistency Notes

Generated: 2026-06-18
Project: PROTEOSTASIS
Scope: PN consistency rereview against local AIGR review and available deep-research artifacts
UniProt: Q86YB8
AIGR review status: COMPLETE
Review batch: proteostasis-batch-2026-06-07b
Batch change status: added

Source Files Checked

AIGR review YAML: present - genes/human/ERO1B/ERO1B-ai-review.yaml
AIGR review HTML: present - genes/human/ERO1B/ERO1B-ai-review.html
Gene notes: present - genes/human/ERO1B/ERO1B-notes.md
GOA TSV: present - genes/human/ERO1B/ERO1B-goa.tsv
UniProt record: present - genes/human/ERO1B/ERO1B-uniprot.txt
PN dossier: projects/PROTEOSTASIS/reports/phase1_dossiers/ERO1B.md
PN consistency section: projects/PROTEOSTASIS/reports/phase1_dossiers/_sections/ERO1B.md
PN projection report: projects/PROTEOSTASIS/reports/pn_projection/pn_projected_gene_go_summary.tsv
PN mapping audit: projects/PROTEOSTASIS/reports/pn_mapping_audit/current_mapping_scrutiny.tsv

Deep Research Files

No *-deep-research*.md file found in this gene directory.

AIGR Review Snapshot

Description: ERO1B (ERO1-like protein beta, formerly ERO1LB; endoplasmic reticulum oxidoreductin-1 beta) is an ER membrane-associated, FAD-dependent flavoprotein sulfhydryl oxidase (EC 1.8.3.2) and a paralog of ERO1A. It drives oxidative protein folding in the endoplasmic reticulum by reoxidizing the protein disulfide isomerase P4HB/PDI (and, less efficiently, other PDI-family members), regenerating their active-site disulfides so they can catalyze further disulfide-bond formation in secretory proteins; the abstracted electrons are passed via bound FAD to molecular oxygen, producing hydrogen peroxide. It is a peripheral membrane protein on the lumenal side of the ER (and is retained there in part through interaction with ERP44), and forms disulfide-linked homodimers as well as heterodimers with ERO1A. Compared with ERO1A it is intrinsically more active and more loosely regulated, consistent with its enrichment in professional secretory tissues - particularly the pancreatic islets of Langerhans, stomach chief cells and digestive tract - where high oxidative folding capacity is required. It is induced during the unfolded protein response and has been implicated in oxidative proinsulin folding and glucose homeostasis.
Existing/core annotation action counts: ACCEPT: 15; KEEP_AS_NON_CORE: 6; MARK_AS_OVER_ANNOTATED: 4

PN Consistency Summary

Consistency: Notes, review YAML, and the corrected PN type mapping agree: ERO1B is an FAD-dependent sulfhydryl OXIDASE (paralog of ERO1A, more active/loosely regulated, secretory-tissue enriched) that reoxidizes PDI. Review core MF = GO:0016971 (EXP PMID:11707400/21091435, ACCEPT) and it MARK_AS_OVER_ANNOTATED the GO:0015035 protein-disulfide reductase rows (IEA + three Reactome EXP rows) for wrong directionality. Same internal PN tension as ERO1A: the parent group still maps GO:0003756 and the projected list still projects GO:0003756 to ERO1B as new_to_goa, contradicting the corrected type node and the review.
PN story / NEW pressure: GO:0016971 (OLS-verified) is in GOA (EXP) and ACCEPTed — captured. GO:0003756 (verified real) should NOT be added: ERO1B is an oxidase, not an isomerase (the review never asserts isomerase activity and rejects the reductase mislabel). Conclusion on the group projection: over-reaches for ERO1B. One nuance the review surfaces that PN does not: a genuine tissue-specific role in oxidative proinsulin folding (GO:0030070 insulin processing, KEEP_AS_NON_CORE) — enrichment, not conflict.
Evidence alignment: PN dossier lists no reference titles. Review oxidase evidence (PMID:11707400, 21091435, 10818100; plus the rejected reductase sources PMID:16407158, 21091435 Reactome) is reviewer-supplied. ERO1B↔P4HB relay biology mirrors the P4HB review. Alignment by shared biology, not citation list.
Verdict: Consistent at the (corrected) gene/type level; GO:0016971 validated and captured. The group-level GO:0003756 projection over-reaches and should not land on ERO1B (same fix as ERO1A). Recommended edits: [MAP] suppress/override the GO:0003756 projection for ERO1B so PDI-reoxidation oxidase children inherit only GO:0016971 (consistent with the corrected type node and the review's explicit oxidase-not-isomerase / not-reductase stance).

Full Consistency Review

UniProt: Q86YB8 · batch: proteostasis-batch-2026-06-07b · review status: COMPLETE
PN placement: ER proteostasis|Folding enzyme|Protein disulfide isomerases|Protein disulfide isomerase reoxidation. PN-node mapping: type PDI reoxidation=mapped→GO:0016971 flavin-dependent sulfhydryl oxidase activity (corrected in batch-5); parent group Protein disulfide isomerases=mapped→GO:0003756 protein disulfide isomerase activity (new_to_goa); class/branch=no_mapping. (Identical node/mapping structure to ERO1A.)
Consistency: Notes, review YAML, and the corrected PN type mapping agree: ERO1B is an FAD-dependent sulfhydryl OXIDASE (paralog of ERO1A, more active/loosely regulated, secretory-tissue enriched) that reoxidizes PDI. Review core MF = GO:0016971 (EXP PMID:11707400/21091435, ACCEPT) and it MARK_AS_OVER_ANNOTATED the GO:0015035 protein-disulfide reductase rows (IEA + three Reactome EXP rows) for wrong directionality. Same internal PN tension as ERO1A: the parent group still maps GO:0003756 and the projected list still projects GO:0003756 to ERO1B as new_to_goa, contradicting the corrected type node and the review.
PN story / NEW pressure: GO:0016971 (OLS-verified) is in GOA (EXP) and ACCEPTed — captured. GO:0003756 (verified real) should NOT be added: ERO1B is an oxidase, not an isomerase (the review never asserts isomerase activity and rejects the reductase mislabel). Conclusion on the group projection: over-reaches for ERO1B. One nuance the review surfaces that PN does not: a genuine tissue-specific role in oxidative proinsulin folding (GO:0030070 insulin processing, KEEP_AS_NON_CORE) — enrichment, not conflict.
Mapping strategy: Type-level correction (→GO:0016971) is right; the residual group-level GO:0003756 inheritance is the only problem, arising because Protein disulfide isomerases mixes catalytic isomerases, non-catalytic members and oxidases. ERO1B is the cleanest illustration: it carries three EXP reductase rows that the review actively rejects on directionality grounds, so propagating the isomerase term to it is doubly inappropriate.
Evidence alignment: PN dossier lists no reference titles. Review oxidase evidence (PMID:11707400, 21091435, 10818100; plus the rejected reductase sources PMID:16407158, 21091435 Reactome) is reviewer-supplied. ERO1B↔P4HB relay biology mirrors the P4HB review. Alignment by shared biology, not citation list.
Verdict: Consistent at the (corrected) gene/type level; GO:0016971 validated and captured. The group-level GO:0003756 projection over-reaches and should not land on ERO1B (same fix as ERO1A). Recommended edits: [MAP] suppress/override the GO:0003756 projection for ERO1B so PDI-reoxidation oxidase children inherit only GO:0016971 (consistent with the corrected type node and the review's explicit oxidase-not-isomerase / not-reductase stance).

PN Dossier Context

review_batch: proteostasis-batch-2026-06-07b
review_yaml: genes/human/ERO1B/ERO1B-ai-review.yaml
PN workbook rows: 1

PN row 1: ER proteostasis | Folding enzyme | Protein disulfide isomerases | Protein disulfide isomerase reoxidation

UniProt: Q86YB8
In branches: ER
PN-node mapping records (path + ancestors):
- [type] ER proteostasis|Folding enzyme|Protein disulfide isomerases|Protein disulfide isomerase reoxidation
  status=mapped scope=ok_for_propagation_to_go GO=[GO:0016971 flavin-dependent sulfhydryl oxidase activity]
  rationale: Corrected after gene-level review (proteostasis batch 5). This PN type is the ERO1 "PDI reoxidation" step, whose members (ERO1A/ERO1L, ERO1B/ERO1LB) are FAD-dependent sulfhydryl OXIDASES that reoxidize PDI to regenerate its active site — they do not themselves catalyze protein disulfide isomerization. The previous target GO:0003756 (protein disulfide isomerase activity) was incorrect for this node and would mislabel the oxidases as isomerases (both ERO1A and ERO1B reviews mark the protein-disulfide reductase/isomerase terms as over-annotations). The correct shared molecular function is GO:0016971 flavin-dependent sulfhydryl oxidase activity, which both genes carry with experimental (EXP) evidence in GOA.
- [group] ER proteostasis|Folding enzyme|Protein disulfide isomerases
  status=mapped scope=ok_for_propagation_to_go GO=[GO:0003756 protein disulfide isomerase activity]
  rationale: This PN group captures the canonical ER protein-disulfide-isomerase folding enzymes. GO protein disulfide isomerase activity is the cleanest propagation target for the catalytically active family members.
- [class] ER proteostasis|Folding enzyme
  status=no_mapping scope= GO=[]
  rationale: Reviewed as a broad PN category rather than a single GO class. The member genes span multiple activities, complexes, or contexts, so direct propagation from this node would overstate the shared biology.
- [branch] ER proteostasis
  status=no_mapping scope= GO=[]
  rationale: Reviewed as a top-level PN branch. This is a systems/taxonomy umbrella, not a direct GO assertion; narrower child curations carry any propagating GO mappings.

Projected GO annotations (2)

GO:0003756 protein disulfide isomerase activity | scope=ok_for_propagation_to_go | goa_status=new_to_goa | from=ER proteostasis|Folding enzyme|Protein disulfide isomerases
GO:0003756 protein disulfide isomerase activity | scope=ok_for_propagation_to_go | goa_status=new_to_goa | from=ER proteostasis|Folding enzyme|Protein disulfide isomerases|Protein disulfide isomerase reoxidation

Note

This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.

📄 View Raw YAML

id: Q86YB8
gene_symbol: ERO1B
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: ERO1B (ERO1-like protein beta, formerly ERO1LB; endoplasmic reticulum oxidoreductin-1 beta) is an ER membrane-associated, FAD-dependent flavoprotein sulfhydryl oxidase (EC 1.8.3.2) and a paralog of ERO1A. It drives oxidative protein folding in the endoplasmic reticulum by reoxidizing the protein disulfide isomerase P4HB/PDI (and, less efficiently, other PDI-family members), regenerating their active-site disulfides so they can catalyze further disulfide-bond formation in secretory proteins; the abstracted electrons are passed via bound FAD to molecular oxygen, producing hydrogen peroxide. It is a peripheral membrane protein on the lumenal side of the ER (and is retained there in part through interaction with ERP44), and forms disulfide-linked homodimers as well as heterodimers with ERO1A. Compared with ERO1A it is intrinsically more active and more loosely regulated, consistent with its enrichment in professional secretory tissues - particularly the pancreatic islets of Langerhans, stomach chief cells and digestive tract - where high oxidative folding capacity is required. It is induced during the unfolded protein response and has been implicated in oxidative proinsulin folding and glucose homeostasis.
existing_annotations:
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: ERO1B is a peripheral ER membrane protein on the lumenal side; this is its primary site of action, supported experimentally and by phylogenetic inference.
    action: ACCEPT
    reason: The ER membrane (lumenal side) is the documented site where ERO1B reoxidizes PDI; corroborated by direct subcellular-location evidence.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum membrane'
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: located_in
  review:
    summary: ER localization is correct and the principal compartment for ERO1B.
    action: ACCEPT
    reason: ERO1B is an ER-resident oxidase; directly supported by immunofluorescence and glycosylation evidence.
    supported_by:
    - reference_id: PMID:10818100
      supporting_text: the products of the ERO1-Lbeta gene are primarily localized in the ER of mammalian cells
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Electronic ER-membrane localization, consistent with experimental and IBA evidence.
    action: ACCEPT
    reason: Correct compartment; ERO1B is a peripheral ER membrane protein.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: Peripheral membrane protein
- term:
    id: GO:0015035
    label: protein-disulfide reductase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: This term asserts a disulfide REDUCTASE activity. ERO1B is mechanistically an OXIDASE that reoxidizes (forms disulfides in) PDI; the reductase label misrepresents the catalytic direction.
    action: MARK_AS_OVER_ANNOTATED
    reason: ERO1B oxidizes PDI and passes electrons to O2 generating H2O2; the physiological direction is dithiol oxidation, not disulfide reduction, so a reductase annotation is an over-annotation.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: Efficiently reoxidizes P4HB/PDI, the enzyme catalyzing protein disulfide formation, in order to allow P4HB to sustain additional rounds of disulfide formation.
- term:
    id: GO:0016971
    label: flavin-dependent sulfhydryl oxidase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000116
  qualifier: enables
  review:
    summary: This is the precise core molecular function of ERO1B - a FAD-dependent sulfhydryl oxidase catalyzing dithiol + O2 = disulfide + H2O2 (RHEA:59116).
    action: ACCEPT
    reason: Matches the catalytic activity and FAD cofactor of ERO1B; supported by EXP evidence (PMID:11707400, PMID:21091435).
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: 'Reaction=[protein]-dithiol + O2 = [protein]-disulfide + H2O2'
- term:
    id: GO:0016972
    label: thiol oxidase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: Thiol oxidase activity is the broader parent of ERO1B's flavin-dependent sulfhydryl oxidase activity; correct but less specific.
    action: ACCEPT
    reason: Correctly captures ERO1B's oxidase activity; the EXP/IDA versions of the same term confirm it.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: 'EC=1.8.3.2'
- term:
    id: GO:0034975
    label: protein folding in endoplasmic reticulum
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: ERO1B drives oxidative protein folding in the ER; this is a valid downstream process outcome of its oxidase activity.
    action: KEEP_AS_NON_CORE
    reason: Protein folding in the ER is the biological-process consequence of the oxidase activity rather than ERO1B's direct molecular function.
    supported_by:
    - reference_id: PMID:21091435
      supporting_text: drives oxidative protein folding
- term:
    id: GO:0071949
    label: FAD binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: ERO1B is a flavoprotein that binds FAD as its cofactor.
    action: ACCEPT
    reason: FAD is the documented cofactor (PMID:21091435), integral to the oxidase mechanism; FAD binding residues are mapped.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: 'Name=FAD; Xref=ChEBI:CHEBI:57692'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:20802462
  qualifier: enables
  review:
    summary: IntAct interaction with PDIA3/ERp57 (P30101). The bare protein binding term is uninformative; it records an interaction within the ER oxidoreductase network.
    action: KEEP_AS_NON_CORE
    reason: Records a real physical interaction (PDIA3), but the generic protein binding term is uninformative and the informative function is the oxidase MF; ERO1B's principal PDI substrate is P4HB.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: 'Q86YB8; P30101: PDIA3'
- term:
    id: GO:0005788
    label: endoplasmic reticulum lumen
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: is_active_in
  review:
    summary: ERO1B acts on the lumenal side of the ER membrane; ER lumen is consistent with its site of action.
    action: ACCEPT
    reason: ERO1B is a lumenal-side ER protein; ER lumen localization is consistent with its function.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: Lumenal side
- term:
    id: GO:0015036
    label: disulfide oxidoreductase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: enables
  review:
    summary: A directionless parent term for thiol-disulfide oxidoreduction; correctly captures ERO1B's catalytic chemistry without mislabeling it as a reductase.
    action: ACCEPT
    reason: Accurate (direction-neutral) molecular-function term for an enzyme that interconverts dithiols and disulfides on PDI; subsumed by the more specific sulfhydryl oxidase term.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: Oxidoreductase involved in disulfide bond formation in the endoplasmic reticulum.
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: Generic membrane localization; ERO1B is a peripheral membrane protein, so this is consistent but uninformative.
    action: KEEP_AS_NON_CORE
    reason: Correct but generic; the specific ER membrane term is preferred.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: Peripheral membrane protein
- term:
    id: GO:0030070
    label: insulin processing
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-264876
  qualifier: involved_in
  review:
    summary: ERO1B may drive oxidative proinsulin folding in pancreatic beta cells, contributing to insulin processing; a genuine but specialized, tissue-restricted role. Recent proteomic work corroborates ERO1B enrichment in beta cells and its association with insulin biogenesis.
    action: KEEP_AS_NON_CORE
    reason: Supported as a plausible specialized function in pancreatic islets (where ERO1B is enriched), but it is a tissue-specific downstream role rather than the core oxidase function. The falcon deep research synthesizes recent proteomic data (axelsson2024) identifying ERO1B as enriched in pancreatic beta cells and implicated in insulin biogenesis, consistent with this annotation; this remains a specialized downstream process rather than the core MF.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: May be involved in oxidative proinsulin folding in pancreatic cells, hence may play a role in glucose homeostasis.
    - reference_id: file:human/ERO1B/ERO1B-deep-research-falcon.md
      supporting_text: ERO1B plays a specialized role in supporting the high protein secretory load of pancreatic beta cells, particularly for the folding and maturation of proinsulin
    - reference_id: file:human/ERO1B/ERO1B-deep-research-falcon.md
      supporting_text: Single-cell proteomics of human pancreatic islet cells found that ERO1B expression was higher in beta cells
- term:
    id: GO:0016971
    label: flavin-dependent sulfhydryl oxidase activity
  evidence_type: EXP
  original_reference_id: PMID:11707400
  qualifier: enables
  review:
    summary: Experimentally supported FAD-dependent sulfhydryl oxidase activity - ERO1B facilitates disulfide bond formation by oxidizing PDI.
    action: ACCEPT
    reason: Direct experimental evidence (selective oxidation of PDI); core molecular function.
    supported_by:
    - reference_id: PMID:11707400
      supporting_text: both human Ero1-Lalpha and Ero1-Lbeta (hEROs) facilitate disulfide bond formation in immunoglobulin subunits by selectively oxidizing PDI
- term:
    id: GO:0016971
    label: flavin-dependent sulfhydryl oxidase activity
  evidence_type: EXP
  original_reference_id: PMID:21091435
  qualifier: enables
  review:
    summary: Experimentally supported FAD-dependent sulfhydryl oxidase activity; recombinant ERO1B is twice as active as ERO1A and oxidizes PDI efficiently. ERO1B acts on PDI (not client proteins directly) via a two-step ERO1-PDI relay.
    action: ACCEPT
    reason: Direct enzymatic-assay evidence for the core oxidase function; ERO1B is a highly active, loosely regulated oxidase. The falcon deep research reinforces that ERO1B's catalytic substrate is reduced PDI, which it re-oxidizes so PDI can in turn introduce disulfide bonds into nascent secretory proteins.
    supported_by:
    - reference_id: PMID:21091435
      supporting_text: recombinant human Ero1β is twice as active as Ero1α in enzymatic assays
    - reference_id: file:human/ERO1B/ERO1B-deep-research-falcon.md
      supporting_text: 'ERO1B does not directly oxidize client secretory proteins; instead, it functions in a two-step relay system'
- term:
    id: GO:0016972
    label: thiol oxidase activity
  evidence_type: EXP
  original_reference_id: PMID:11707400
  qualifier: enables
  review:
    summary: Experimentally supported thiol oxidase activity (parent of the flavin-dependent sulfhydryl oxidase term).
    action: ACCEPT
    reason: EXP evidence for oxidase activity; correct core function, though the flavin-dependent sulfhydryl oxidase term is the most precise.
    supported_by:
    - reference_id: PMID:11707400
      supporting_text: both human Ero1-Lalpha and Ero1-Lbeta (hEROs) facilitate disulfide bond formation in immunoglobulin subunits by selectively oxidizing PDI
- term:
    id: GO:0005788
    label: endoplasmic reticulum lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9817575
  qualifier: located_in
  review:
    summary: Reactome ER-lumen localization, consistent with ERO1B's lumenal-side site of action.
    action: ACCEPT
    reason: Consistent with the documented lumenal-side ER localization.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: Lumenal side
- term:
    id: GO:0015035
    label: protein-disulfide reductase activity
  evidence_type: EXP
  original_reference_id: PMID:11707400
  qualifier: enables
  review:
    summary: This Reactome EXP annotation labels ERO1B as a protein-disulfide REDUCTASE. ERO1B physically engages PDI active-site disulfides, but its physiological action is oxidation of PDI (forming disulfides), not reduction; the reductase label is directionally misleading.
    action: MARK_AS_OVER_ANNOTATED
    reason: The supporting study shows ERO1B/ERO1 oxidizes PDI; the reductase directionality mischaracterizes the enzyme, which is an oxidase. The accurate term is sulfhydryl oxidase / disulfide oxidoreductase activity.
    supported_by:
    - reference_id: PMID:11707400
      supporting_text: both human Ero1-Lalpha and Ero1-Lbeta (hEROs) facilitate disulfide bond formation in immunoglobulin subunits by selectively oxidizing PDI
- term:
    id: GO:0015035
    label: protein-disulfide reductase activity
  evidence_type: EXP
  original_reference_id: PMID:16407158
  qualifier: enables
  review:
    summary: Reactome EXP reductase annotation. As above, the ERO1 enzyme generates disulfides (oxidase); the reductase directionality is misleading.
    action: MARK_AS_OVER_ANNOTATED
    reason: The cited work concerns enzymatic disulfide generation by the ER thiol oxidase Ero1; an oxidase, not a reductase. The reductase term over-annotates the catalytic direction.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: Following P4HB reoxidation, passes its electrons to molecular oxygen via FAD
- term:
    id: GO:0015035
    label: protein-disulfide reductase activity
  evidence_type: EXP
  original_reference_id: PMID:21091435
  qualifier: enables
  review:
    summary: Reactome EXP reductase annotation derived from the Ero1β characterization, which actually shows ERO1B oxidizes PDI; the reductase directionality is misleading.
    action: MARK_AS_OVER_ANNOTATED
    reason: The supporting study demonstrates oxidase activity (oxidizing PDI), not disulfide reduction; the reductase term mislabels the catalytic direction.
    supported_by:
    - reference_id: PMID:21091435
      supporting_text: Ero1β oxidizes PDI more efficiently than other PDI family members
- term:
    id: GO:0034975
    label: protein folding in endoplasmic reticulum
  evidence_type: IDA
  original_reference_id: PMID:21091435
  qualifier: involved_in
  review:
    summary: ERO1B drives oxidative protein folding in the ER; protein folding in the ER is a downstream process of its oxidase activity.
    action: KEEP_AS_NON_CORE
    reason: A valid process annotation supported by direct evidence, but downstream of the core oxidase molecular function.
    supported_by:
    - reference_id: PMID:21091435
      supporting_text: drives oxidative protein folding
- term:
    id: GO:0016972
    label: thiol oxidase activity
  evidence_type: IDA
  original_reference_id: PMID:21091435
  qualifier: enables
  review:
    summary: Direct-assay thiol oxidase activity confirmed for recombinant ERO1B.
    action: ACCEPT
    reason: IDA evidence for the core oxidase activity from enzymatic assays.
    supported_by:
    - reference_id: PMID:21091435
      supporting_text: recombinant human Ero1β is twice as active as Ero1α in enzymatic assays
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: TAS
  original_reference_id: PMID:10818100
  qualifier: located_in
  review:
    summary: ERO1-Lbeta is primarily localized in the ER (immunofluorescence, endoglycosidase sensitivity, in vitro translocation).
    action: ACCEPT
    reason: TAS from the founding characterization directly establishes ER localization.
    supported_by:
    - reference_id: PMID:10818100
      supporting_text: the products of the ERO1-Lbeta gene are primarily localized in the ER of mammalian cells
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: TAS
  original_reference_id: PMID:10818100
  qualifier: involved_in
  review:
    summary: ERO1-Lbeta generates oxidative conditions in the ER required for disulfide bond formation; protein folding is the downstream process.
    action: KEEP_AS_NON_CORE
    reason: A valid process annotation but downstream of the core oxidase molecular function.
    supported_by:
    - reference_id: PMID:10818100
      supporting_text: ERO1-Lbeta is involved also in generating oxidative conditions in the ER
- term:
    id: GO:0016491
    label: oxidoreductase activity
  evidence_type: NAS
  original_reference_id: PMID:10818100
  qualifier: enables
  review:
    summary: ERO1B is an oxidoreductase; a correct but very general parent term.
    action: ACCEPT
    reason: Correct high-level molecular function, subsumed by the more specific flavin-dependent sulfhydryl oxidase activity.
    supported_by:
    - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
      supporting_text: Oxidoreductase involved in disulfide bond formation in the endoplasmic reticulum.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB Subcellular Location vocabulary mapping
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000116
  title: Gene Ontology annotation based on RHEA mapping of reactions
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:10818100
  title: Endoplasmic reticulum oxidoreductin 1-lbeta (ERO1-Lbeta), a human gene induced in the course of the unfolded protein response.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: "Cached publications/PMID_10818100.md title matches YAML; original identification of ERO1B as an ER oxidoreductin generating oxidative ER conditions. GOA anchors this PMID to ER localization (GO:0005783) and protein folding (GO:0006457)."
  findings:
  - statement: ERO1-Lbeta is a human EROs-family gene primarily localized to the ER, able to generate oxidative conditions in the ER (complementing the yeast ero1-1 mutant), with a distinct tissue distribution from ERO1-L and uniquely induced during the unfolded protein response.
    reference_section_type: ABSTRACT
- id: PMID:11707400
  title: Manipulation of oxidative protein folding and PDI redox state in mammalian cells.
  findings:
  - statement: Both human Ero1-Lalpha and Ero1-Lbeta facilitate disulfide bond formation in immunoglobulin subunits by selectively oxidizing PDI.
    reference_section_type: ABSTRACT
- id: PMID:16407158
  title: 'Generating disulfides enzymatically: reaction products and electron acceptors of the endoplasmic reticulum thiol oxidase Ero1p.'
  findings:
  - statement: Characterizes the ER thiol oxidase Ero1 mechanism of enzymatic disulfide generation and electron acceptors (oxidase chemistry).
    reference_section_type: ABSTRACT
- id: PMID:20802462
  title: Disulphide production by Ero1α-PDI relay is rapid and effectively regulated.
  findings: []
- id: PMID:21091435
  title: The endoplasmic reticulum sulfhydryl oxidase Ero1β drives efficient oxidative protein folding with loose regulation.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: "Cached publications/PMID_21091435.md title matches YAML; biochemically establishes the core MF — recombinant Ero1β is a sulfhydryl oxidase that oxidizes PDI and drives oxidative folding. GOA anchors this PMID to GO:0016971/GO:0016972 (flavin-dependent sulfhydryl oxidase, EXP/IDA) and GO:0015035."
  findings:
  - statement: Recombinant human Ero1β is twice as active as Ero1α, oxidizes PDI more efficiently than other PDI family members, drives oxidative protein folding preferentially via the a domain of PDI, and is loosely regulated (Cys130 critical for feedback); it is constitutively expressed in professional secretory tissues and UPR-induced.
    reference_section_type: ABSTRACT
- id: Reactome:R-HSA-264876
  title: Insulin processing
  findings: []
- id: Reactome:R-HSA-9817575
  title: Reactome ER-lumen oxidative folding annotation for ERO1B
  findings: []
- id: file:human/ERO1B/ERO1B-uniprot.txt
  title: UniProt entry Q86YB8 (ERO1B_HUMAN), ERO1-like protein beta
  findings:
  - statement: FAD-dependent ER sulfhydryl oxidase (EC 1.8.3.2) that reoxidizes P4HB/PDI (and other PDI-family members at lower rates) to drive disulfide-bond formation, passing electrons to O2 via FAD; peripheral lumenal-side ER membrane protein, homodimeric and heterodimeric with ERO1A; enriched in pancreatic islets and digestive tract; UPR-induced; implicated in proinsulin folding/glucose homeostasis.
    reference_section_type: OTHER
- id: file:human/ERO1B/ERO1B-deep-research-falcon.md
  title: Falcon deep research report for ERO1B
  reference_review:
    relevance: MEDIUM
    correctness: UNVERIFIED
    review_notes: "LLM-synthesized (Edison/Falcon) report. Useful corroboration on several
      points: it correctly frames ERO1B as acting via a two-step ERO1-PDI relay (it
      oxidizes PDI rather than client proteins directly) and reiterates ER-lumen
      localization, redox-regulated activity, H2O2 production, and PRDX4/GPX7/GPX8
      functional redundancy. The ERO1B-SPECIFIC claims that are genuinely supported are
      the preferential expression in secretory tissues/pancreatic beta cells and the
      proteomic association with insulin biogenesis (axelsson2024 proteomic/islet
      single-cell data). MANY mechanistic statements (regulatory-disulfide residue
      numbering Cys94-Cys131/Cys99-Cys104, ~25% of translational H2O2, regulatory
      switch behavior) are explicitly generalized from ERO1A 'by extension' and are NOT
      independently demonstrated for ERO1B; these are treated as ERO1A-derived
      inferences and not used to alter annotations. Primary-literature DOIs cited in the
      report (e.g. zito2024, axelsson2024) were not individually re-verified here, hence
      UNVERIFIED."
core_functions:
- description: FAD-dependent endoplasmic-reticulum sulfhydryl oxidase that reoxidizes the protein disulfide isomerase P4HB/PDI, regenerating PDI's active site to sustain disulfide-bond formation in secretory proteins, with electrons passed via FAD to O2 producing H2O2; intrinsically more active and more loosely regulated than ERO1A.
  molecular_function:
    id: GO:0016971
    label: flavin-dependent sulfhydryl oxidase activity
  locations:
  - id: GO:0005789
    label: endoplasmic reticulum membrane
  - id: GO:0005788
    label: endoplasmic reticulum lumen
  supported_by:
  - reference_id: file:human/ERO1B/ERO1B-uniprot.txt
    supporting_text: Efficiently reoxidizes P4HB/PDI, the enzyme catalyzing protein disulfide formation, in order to allow P4HB to sustain additional rounds of disulfide formation.
  - reference_id: PMID:21091435
    supporting_text: recombinant human Ero1β is twice as active as Ero1α in enzymatic assays
proposed_new_terms: []
suggested_questions:
- question: How is the division of labor between ERO1B and ERO1A (and PRDX4) established in pancreatic beta cells, and how essential is ERO1B specifically for proinsulin oxidative folding and insulin secretion?
- question: Does the looser regulation of ERO1B relative to ERO1A make secretory tissues more vulnerable to ER oxidative stress, and how is its activity feedback-controlled in vivo?
suggested_experiments:
- description: Beta-cell-specific knockout or knockdown of ERO1B (alone and combined with ERO1A) followed by assays of proinsulin folding, insulin secretion and ER redox state to test its role in glucose homeostasis.
- description: Comparative enzymology of purified ERO1B versus ERO1A measuring O2 consumption, H2O2 production and PDI-isoform substrate preference, including the regulatory-disulfide mutants (e.g. Cys130) that govern feedback control.

ERO1B

Gene Description

Existing Annotations Review

Core Functions

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Comprehensive Research Report: ERO1B (Endoplasmic Reticulum Oxidoreductase 1 Beta)

Gene and Protein Identity

Primary Molecular Function and Enzymatic Activity

Core Enzymatic Function

Catalyzed Reaction

Substrate Specificity

Subcellular Localization

Signaling and Biochemical Pathways

Oxidative Protein Folding Pathway

Regulation by Redox-Dependent Mechanisms

Unfolded Protein Response (UPR) and ER Stress

Redox Homeostasis and ROS Production

Functional Redundancy with Alternative Oxidases

Biological Processes and Physiological Roles

Tissue-Specific Expression

Role in Pancreatic Beta Cell Function and Insulin Biogenesis

Association with Respiratory Function

Protein Secretion and ER Proteostasis

Evolutionary and Structural Context

Recent Developments and Current Understanding (2023-2025)

Recent Clinical and Physiological Studies

Understanding of Redundancy and Compensation

Regulation and Feedback Mechanisms

Summary Table

Conclusions

Artifacts

Citations

📚 Additional Documentation

Notes

ERO1B (ERO1LB, ERO1-Lbeta) research notes

Core molecular function

Tissue / biology

Action plan

Pn Notes

ERO1B PN Consistency Notes

Source Files Checked

Deep Research Files

AIGR Review Snapshot

PN Consistency Summary

Full Consistency Review

PN Dossier Context

PN row 1: ER proteostasis | Folding enzyme | Protein disulfide isomerases | Protein disulfide isomerase reoxidation

Projected GO annotations (2)

Note

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