LRG1 is a secreted, extensively glycosylated leucine-rich-repeat protein produced as a 347-amino-acid precursor with a cleaved signal peptide (residues 1-35) and an eight-LRR mature chain (residues 36-347). It circulates in plasma and is produced prominently by hepatocytes and neutrophils. LRG1 has no known catalytic activity; it functions extracellularly as a context-dependent receptor-binding and signaling modulator. In endothelial cells exposed to TGF-beta, LRG1 binds endoglin and type I and type II TGF-beta receptor components, favors the pro-angiogenic ALK1-SMAD1/5 branch, and promotes endothelial proliferation and angiogenesis. In mouse fibroblasts it can instead enhance TGF-beta-SMAD2 signaling and profibrotic responses without requiring endoglin, illustrating that its signaling output depends on cellular receptor context. LRG1 glycosylation also gates a distinct interaction with the adhesion G protein-coupled receptor LPHN2: removal of the N325 glycan increases receptor binding and LPHN2-dependent angiogenic and neurotrophic activity in experimental systems. LRG1 additionally contributes to inflammatory-cell, re-epithelialization, vascular, and NETosis responses during wound repair, with opposing net effects in normal and diabetic mouse wounds. No alternative protein isoforms are reported.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005576 extracellular region | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference places active LRG1 in the extracellular region. Reason: LRG1 is a signal-peptide-containing secreted glycoprotein, so this broad active compartment is correct and central to its receptor-modulating function. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN008456974 UniProtKB:P02750 |
| GO:0005114 type II transforming growth factor beta receptor binding | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference assigns binding to type II TGF-beta receptors. Reason: Direct human experiments independently show LRG1 interaction with TGFBR2, making the conserved inference biologically sound and core. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN008456974 UniProtKB:P02750 |
| GO:0030511 positive regulation of transforming growth factor beta receptor signaling pathway | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference assigns positive regulation of TGF-beta receptor signaling. Reason: Human LRG1 reorganizes the endothelial TGF-beta receptor complex toward pro-angiogenic SMAD1/5 signaling; this is a central mechanistic process. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN008456974 UniProtKB:P02750 |
| GO:0034713 type I transforming growth factor beta receptor binding | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference assigns binding to type I TGF-beta receptors. Reason: Direct human experiments show LRG1 association with ALK1 and ALK5, independently supporting this conserved molecular function. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN008456974 UniProtKB:P02750 |
| GO:0035313 wound healing, spreading of epidermal cells | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic inference assigns a role in epidermal spreading during wound healing. Reason: LRG1-dependent keratinocyte migration and re-epithelialization support the term, but it is a tissue-specific downstream outcome of extracellular signaling. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN008456974 UniProtKB:P02750 |
| GO:0045766 positive regulation of angiogenesis | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference assigns positive regulation of angiogenesis. Reason: Angiogenesis is a well-supported major output of LRG1-mediated TGF-beta receptor-complex modulation in endothelial cells. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN008456974 UniProtKB:P02750 |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | ACCEPT | Summary: Automated orthology and UniProt subcellular-location mappings place LRG1 extracellularly. Reason: The mouse ortholog transfer and secreted-location mapping agree with the human signal peptide, plasma protein identity, and curated secretion statement. Propagation Review Root cause: NO FAILURE CORE Sources checked: UniProtKB:Q91XL1 ensembl:ENSMUSP00000038048 UniProtKB-SubCell:SL-0243 |
| GO:0005515 protein binding | IPI PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | MODIFY | Summary: Interaction experiments detect LRG1 binding to the TGF-beta accessory receptor endoglin. Reason: The interaction is well supported, but generic protein binding is uninformative; type III transforming growth factor beta receptor binding precisely captures interaction with endoglin. Proposed replacements: type III transforming growth factor beta receptor binding Supporting Evidence: PMID:23868260 In primary brain ECs LRG1 was present in immunoprecipitates of TΞ²RII, ALK1, ALK5 and the auxiliary receptor ENG (Fig 4a). |
| GO:0005515 protein binding | IPI PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | MODIFY | Summary: Interaction experiments detect LRG1 binding to the type I TGF-beta receptor ALK5/TGFBR1. Reason: The interaction is well supported, but the partner supports the more informative type I transforming growth factor beta receptor binding term. Proposed replacements: type I transforming growth factor beta receptor binding Supporting Evidence: PMID:23868260 In primary brain ECs LRG1 was present in immunoprecipitates of TΞ²RII, ALK1, ALK5 and the auxiliary receptor ENG (Fig 4a). |
| GO:0005515 protein binding | IPI PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | MODIFY | Summary: Interaction experiments detect LRG1 association with the type I TGF-beta receptor ALK1/ACVRL1. Reason: Generic protein binding loses the biologically informative receptor identity; type I transforming growth factor beta receptor binding is the appropriate specific term. Proposed replacements: type I transforming growth factor beta receptor binding Supporting Evidence: PMID:23868260 In primary brain ECs LRG1 was present in immunoprecipitates of TΞ²RII, ALK1, ALK5 and the auxiliary receptor ENG (Fig 4a). |
| GO:0005515 protein binding | IPI PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | MODIFY | Summary: Interaction experiments detect LRG1 binding to TGFBR2. Reason: Generic protein binding should be replaced by the directly supported type II transforming growth factor beta receptor binding term. Proposed replacements: type II transforming growth factor beta receptor binding Supporting Evidence: PMID:23868260 Immunoprecipitation of the receptor ectodomain revealed coimmunoprecipitation of LRG1 with ALK5, TΞ²RII and ENG indicating a direct interaction of LRG1 with these individual receptors (Fig 4b). |
| GO:0005515 protein binding | IPI PMID:28514442 Architecture of the human interactome defines protein commun... | MARK AS OVER ANNOTATED | Summary: A proteome-scale interaction screen reports LRG1 association with cytochrome c. Reason: Protein binding is uninformative. Targeted surface-plasmon-resonance assays independently show human LRG binding to horse and snake cytochrome c, but not yeast cytochrome c; human CYCS was not tested, and extracellular binding or a physiological role has not been demonstrated in vivo. The high-throughput interaction is therefore retained without promoting it to a core LRG1 function. Supporting Evidence: PMID:20442399 Human LRG bound horse and snake Cyt c with dissociation constants of 1.58 x 10(-13) M and 1.65 x 10(-10) M, respectively, but did not bind yeast Cyt c |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | MARK AS OVER ANNOTATED | Summary: A cell-specific proteome-scale interaction map reports LRG1 association with cytochrome c. Reason: Protein binding is uninformative. Targeted surface-plasmon-resonance assays independently show human LRG binding to horse and snake cytochrome c, but not yeast cytochrome c; human CYCS was not tested, and extracellular binding or a physiological role has not been demonstrated in vivo. The high-throughput interaction is therefore retained without promoting it to a core LRG1 function. Supporting Evidence: PMID:20442399 Human LRG bound horse and snake Cyt c with dissociation constants of 1.58 x 10(-13) M and 1.65 x 10(-10) M, respectively, but did not bind yeast Cyt c |
| GO:0005160 transforming growth factor beta receptor binding | IEA GO_REF:0000107 | ACCEPT | Summary: Ensembl orthology transfer assigns TGF-beta receptor binding from mouse Lrg1. Reason: The orthology transfer is independently corroborated by direct human binding to TGFBR1, TGFBR2, ACVRL1, and endoglin. Propagation Review Root cause: NO FAILURE CORE Sources checked: UniProtKB:Q91XL1 ensembl:ENSMUSP00000038048 |
| GO:0140149 non-collagenous component of interstitial matrix | TAS PMID:36399478 MatrisomeDB 2.0: 2023 updates to the ECM-protein knowledge d... | MARK AS OVER ANNOTATED | Summary: MatrisomeDB curator inference places LRG1 among non-collagenous interstitial-matrix components. Reason: MatrisomeDB supports LRG1 as a secreted matrisome-associated protein, but the available evidence does not establish it as a structural non-collagenous component of interstitial matrix. This cellular-component term therefore overstates the evidence. Supporting Evidence: PMID:36399478 We further divided this in-silico predicted matrisome into two main divisions: (i) structural components of the ECM or the βcore matrisomeβ including ECM glycoproteins, collagens, and proteoglycans, which are highly insoluble in nature and (ii) matrisome-associated proteins including ECM-affiliated proteins, ECM regulators, and secreted factors known or expected to bind to structural components of the ECM. |
| GO:0010718 positive regulation of epithelial to mesenchymal transition | IDA PMID:32887674 A Multifunctional Role of Leucine-Rich Ξ±-2-Glycoprotein 1 in... | KEEP AS NON CORE | Summary: Recombinant and loss-of-function experiments support LRG1 promotion of epithelial-to-mesenchymal transition. Reason: The effect is experimentally supported, but it is a context-dependent cellular response downstream of LRG1 signaling rather than the defining molecular function. Supporting Evidence: PMID:32887674 Our study discovered that rhLRG1 induces the expression of EMT markers, which is consistent with the promoting effect of LRG1 in EMT and colorectal cancer metastasis (16). |
| GO:0001938 positive regulation of endothelial cell proliferation | IMP PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | KEEP AS NON CORE | Summary: LRG1 and TGF-beta1 together stimulate proliferation of mouse brain endothelial cells from WT and Lrg1-null mice. Reason: The cited Fig. 5b experiment directly supports a proliferative output in mouse brain endothelial cells. The occurs_in human umbilical-vein endothelial-cell extension is retained unchanged from the current QuickGO source annotation, but this mouse-cell experiment does not independently establish that cell-type context; proliferation remains a non-core downstream process. Supporting Evidence: PMID:23868260 The addition of LRG1 on its own had no effect, but TGFΞ²1 and LRG1 in combination increased proliferation significantly in both WT and Lrg1 null ECs (Fig 5b). |
| GO:0005114 type II transforming growth factor beta receptor binding | IPI PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | ACCEPT | Summary: A cell-free recombinant receptor-ectodomain assay shows LRG1 binding to TGFBR2. Reason: Co-immunoprecipitation of separately expressed receptor ectodomains in HEK293 conditioned media directly supports this specific molecular function. The occurs_in human umbilical-vein endothelial-cell extension is retained unchanged from the current QuickGO source annotation, but is not established by this cell-free binding assay. Supporting Evidence: PMID:23868260 Immunoprecipitation of the receptor ectodomain revealed coimmunoprecipitation of LRG1 with ALK5, TΞ²RII and ENG indicating a direct interaction of LRG1 with these individual receptors (Fig 4b). |
| GO:0005515 protein binding | IPI PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | MODIFY | Summary: A cell-free recombinant receptor-ectodomain assay shows LRG1 binding to endoglin. Reason: The cell-free receptor-ectodomain interaction is sound, but generic protein binding obscures the biologically relevant interaction with endoglin, a type III TGF-beta receptor. The occurs_in human umbilical-vein endothelial-cell extension is retained unchanged from the current QuickGO source annotation, but is not established by this binding assay. Proposed replacements: type III transforming growth factor beta receptor binding Supporting Evidence: PMID:23868260 LRG1 binds directly to the TGF-Ξ² accessory receptor endoglin, which, in the presence of TGF-Ξ²1, results in promotion of the pro-angiogenic Smad1/5/8 signalling pathway. |
| GO:0010838 positive regulation of keratinocyte proliferation | IMP PMID:32887674 A Multifunctional Role of Leucine-Rich Ξ±-2-Glycoprotein 1 in... | KEEP AS NON CORE | Summary: Lrg1 loss and gain perturb keratinocyte proliferation in wounded skin and cultured keratinocytes. Reason: The proliferative effect is supported, but it is a wound-context downstream response rather than LRG1's defining receptor-binding activity. Supporting Evidence: PMID:32887674 Here, we showed reduced number of proliferating keratinocytes as indicated by Ki67 staining at the wound edge of Lrg1-deficient mice. |
| GO:0030511 positive regulation of transforming growth factor beta receptor signaling pathway | IDA PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | ACCEPT | Summary: LRG1 shifts endothelial TGF-beta signaling toward pro-angiogenic SMAD1/5 activity upstream of endothelial proliferation. Reason: Receptor-complex binding, signaling assays, knockdown, and rescue experiments establish positive modulation of the pathway as a central LRG1 mechanism. Supporting Evidence: PMID:23868260 LRG1 antibody blockade inhibits this switch and attenuates angiogenesis. These studies reveal a new regulator of angiogenesis that mediates its effect by modulating TGF-Ξ² signalling. |
| GO:0030511 positive regulation of transforming growth factor beta receptor signaling pathway | IDA PMID:32887674 A Multifunctional Role of Leucine-Rich Ξ±-2-Glycoprotein 1 in... | ACCEPT | Summary: Wound-healing experiments support LRG1-dependent TGF-beta receptor signaling in skin. Reason: Although assayed in a wound context, the result independently supports the same central receptor-signaling mechanism established in endothelial cells. Supporting Evidence: PMID:32887674 Furthermore, we demonstrated that LRG1-mediated NET formation is dependent on activation of the Akt pathway through TGFΞ² type I receptor ALK5, which is in agreement with LRG1-mediated TGFΞ² signaling in ECs (11), fibroblasts (34), glioma cells (46), and T-helper 17 cells (47). |
| GO:0034713 type I transforming growth factor beta receptor binding | IPI PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | ACCEPT | Summary: A cell-free recombinant receptor-ectodomain assay shows LRG1 binding to ALK5/TGFBR1. Reason: Co-immunoprecipitation of separately expressed receptor ectodomains in HEK293 conditioned media supports this specific and central receptor-binding activity. The occurs_in human umbilical-vein endothelial-cell extension is retained unchanged from the current QuickGO source annotation, but is not established by this cell-free binding assay. Supporting Evidence: PMID:23868260 Immunoprecipitation of the receptor ectodomain revealed coimmunoprecipitation of LRG1 with ALK5, TΞ²RII and ENG indicating a direct interaction of LRG1 with these individual receptors (Fig 4b). |
| GO:0034713 type I transforming growth factor beta receptor binding | IPI PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | ACCEPT | Summary: A cell-free recombinant receptor-ectodomain assay shows endoglin-dependent LRG1 association with ALK1/ACVRL1. Reason: The assay supports an endoglin-dependent association with ALK1 rather than unconditional binary binding. The occurs_in human umbilical-vein endothelial-cell extension is retained unchanged from the current QuickGO source annotation, but is not established by this cell-free ectodomain assay. Supporting Evidence: PMID:23868260 These studies revealed that LRG1 only associated with ALK1 in the presence of ENG, to which it bound, and this was enhanced by the addition of TGFΞ²1 (Fig 4d). |
| GO:0035313 wound healing, spreading of epidermal cells | IMP PMID:32887674 A Multifunctional Role of Leucine-Rich Ξ±-2-Glycoprotein 1 in... | KEEP AS NON CORE | Summary: Lrg1 deficiency delays epidermal spreading and re-epithelialization during cutaneous wound repair. Reason: The wound phenotype is directly supported but is a tissue-specific downstream role rather than the core receptor-modulating molecular function. Supporting Evidence: PMID:32887674 Lrg1 deficiency leads to a significant delay in normal wound healing as a consequence of impaired inflammation, reepithelialization, and angiogenesis. |
| GO:0045766 positive regulation of angiogenesis | IMP PMID:32887674 A Multifunctional Role of Leucine-Rich Ξ±-2-Glycoprotein 1 in... | ACCEPT | Summary: LRG1 promotes vascular growth in the wound bed and in dermal endothelial-cell assays. Reason: This tissue-qualified study independently supports angiogenesis as a major biological output of LRG1 signaling. Supporting Evidence: PMID:32887674 We further showed that LRG1 promotes angiogenesis by mediating HDMEC proliferation, migration, and the ability to form tube-like structures. |
| GO:0045766 positive regulation of angiogenesis | IMP PMID:23868260 LRG1 promotes angiogenesis by modulating endothelial TGF-Ξ² s... | ACCEPT | Summary: Genetic loss, antibody blockade, and endothelial assays show that LRG1 promotes angiogenesis. Reason: The study establishes angiogenesis as a major LRG1 output through endothelial TGF-beta receptor-complex modulation. Supporting Evidence: PMID:23868260 We show that in the presence of transforming growth factor-Ξ²1 (TGF-Ξ²1), LRG1 is mitogenic to endothelial cells and promotes angiogenesis. |
| GO:0051546 keratinocyte migration | IMP PMID:32887674 A Multifunctional Role of Leucine-Rich Ξ±-2-Glycoprotein 1 in... | KEEP AS NON CORE | Summary: LRG1 gain and loss alter keratinocyte migration during re-epithelialization. Reason: Keratinocyte migration is supported as a wound-context response downstream of extracellular LRG1 signaling, but is not a core molecular function. Supporting Evidence: PMID:32887674 Consistent with the previous report (21), we showed that LRG1 overexpression and knockdown affect keratinocyte migration. |
| GO:0060054 positive regulation of epithelial cell proliferation involved in wound healing | IMP PMID:32887674 A Multifunctional Role of Leucine-Rich Ξ±-2-Glycoprotein 1 in... | KEEP AS NON CORE | Summary: Lrg1 deficiency reduces proliferating keratinocytes and delays wound re-epithelialization. Reason: This is a well-supported but tissue-specific downstream wound-healing process. Supporting Evidence: PMID:32887674 Here, we showed reduced number of proliferating keratinocytes as indicated by Ki67 staining at the wound edge of Lrg1-deficient mice. |
| GO:0061756 leukocyte adhesion to vascular endothelial cell | IMP PMID:32887674 A Multifunctional Role of Leucine-Rich Ξ±-2-Glycoprotein 1 in... | KEEP AS NON CORE | Summary: LRG1 promotes neutrophil adhesion and inflammatory-cell recruitment during wound healing. Reason: The IMP evidence supports the leukocyte-adhesion phenotype, but it is a specialized inflammatory outcome rather than the core receptor-binding mechanism. Supporting Evidence: PMID:32887674 Our study showed that LRG1 promotes neutrophil adhesion, likely by inducing the expression of neutrophil adhesion molecule, L-selectin. |
| GO:0005576 extracellular region | HDA PMID:27068509 Extracellular matrix remodelling in response to venous hyper... | ACCEPT | Summary: ECM-enriched proteomics detects LRG1 in human saphenous-vein tissue. Reason: The curated tissue-qualified proteomic localization agrees with LRG1 secretion; extracellular region is broad but correct. Supporting Evidence: PMID:27068509 Varicose saphenous veins removed during phlebectomy and normal saphenous veins obtained during coronary artery bypass surgery were collected for proteomics analysis. Extracellular matrix proteins were enriched from venous tissues. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-6798745 | ACCEPT | Summary: Reactome places LRG1 extracellularly after exocytosis from tertiary neutrophil granules. Reason: The pathway-specific source is consistent with LRG1 being a secreted plasma glycoprotein; the broad extracellular destination is correct. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-6798749 | ACCEPT | Summary: Reactome places LRG1 extracellularly after exocytosis from specific neutrophil granules. Reason: Granule exocytosis supplies a biologically plausible route to the independently established extracellular compartment. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-6800434 | ACCEPT | Summary: Reactome places LRG1 extracellularly after exocytosis from ficolin-1-rich neutrophil granules. Reason: The pathway-specific route is consistent with secretion and supports the broad extracellular localization. |
| GO:0035580 specific granule lumen | TAS Reactome:R-HSA-6798749 | KEEP AS NON CORE | Summary: Reactome assigns LRG1 to the lumen of specific neutrophil granules before exocytosis. Reason: This is a plausible specialized storage compartment linked to neutrophil expression, but it is contextual rather than the general site of LRG1 action. |
| GO:1904724 tertiary granule lumen | TAS Reactome:R-HSA-6798745 | KEEP AS NON CORE | Summary: Reactome assigns LRG1 to the lumen of tertiary neutrophil granules before exocytosis. Reason: The granule localization is compatible with neutrophil production and regulated release, but is a cell-specific storage site. |
| GO:1904813 ficolin-1-rich granule lumen | TAS Reactome:R-HSA-6800434 | KEEP AS NON CORE | Summary: Reactome assigns LRG1 to the lumen of ficolin-1-rich neutrophil granules before exocytosis. Reason: This is a specialized neutrophil storage compartment and not the general extracellular site where released LRG1 acts. |
| GO:0070062 extracellular exosome | HDA PMID:23533145 In-depth proteomic analyses of exosomes isolated from expres... | KEEP AS NON CORE | Summary: Shotgun proteomics detects LRG1 in extracellular exosome preparations from expressed prostatic secretions. Reason: The high-throughput detection is retained with curator deference, but exosome association is sample-specific and not necessary to define LRG1's secreted signaling role. Supporting Evidence: PMID:23533145 Using expressed prostatic secretions in urine (EPS-urine), exosome preparations were characterized by a shotgun proteomics procedure. |
| GO:0005576 extracellular region | HDA PMID:16502470 Human colostrum: identification of minor proteins in the aqu... | ACCEPT | Summary: Proteomics detects LRG1 in the aqueous phase of human colostrum. Reason: Detection in an extracellular body fluid is consistent with LRG1 secretion; the colostrum extension appropriately preserves the sampling context. Supporting Evidence: PMID:16502470 We have investigated the low abundance proteins in the aqueous phase of human colostrum, after depletion of the major proteins secretory IgA, lactoferrin, alpha-lactalbumin and HSA by immunoabsorption, using 2-D LC and gel-based proteomic methods. |
| GO:0005576 extracellular region | IDA PMID:20363744 Prolyl 3-hydroxylase 1 null mice display abnormalities in fi... | ACCEPT | Summary: A curator-assigned experimental annotation places LRG1 in the extracellular region. Reason: The cached record is abstract-only and does not expose the LRG1 assay, so the experimental curator call is retained; extracellular localization is independently clear from LRG1's signal peptide, secretion record, and plasma occurrence. |
| GO:0005576 extracellular region | NAS PMID:12223515 Molecular characterization and expression analysis of leucin... | ACCEPT | Summary: A sequence and expression study supports LRG1 as an extracellular glycoprotein associated with granulocytic differentiation. Reason: Although the cached abstract emphasizes expression rather than localization, the curator statement agrees with the signal peptide and the established identity of mature LRG1 as a circulating secreted protein. |
| GO:0005576 extracellular region | NAS PMID:14718574 The human plasma proteome: a nonredundant list developed by ... | ACCEPT | Summary: Human plasma-proteome evidence places LRG1 in an extracellular body fluid. Reason: Plasma detection directly supports the broad extracellular-region annotation and is concordant with the reviewed UniProt secreted location. Supporting Evidence: PMID:14718574 The resulting nonredundant list confirms the presence of a number of interesting candidate marker proteins in plasma and serum. |
| GO:0016020 membrane | NAS PMID:3856868 Periodicity of leucine and tandem repetition of a 24-amino a... | REMOVE | Summary: An early sequence analysis proposed that LRG1 is membrane-derived or membrane-associated. Reason: The NAS annotation reflects a historical sequence-based hypothesis rather than observed membrane localization. It is superseded by the experimentally supported cleaved signal peptide (residues 1-35), soluble secreted mature plasma protein (residues 36-347), and absence of a transmembrane segment, so the membrane annotation should be removed. Supporting Evidence: PMID:3856868 These structural characteristics and the homology to mitochondrial proteins and apolipoproteins suggest that LRG is a membrane-derived or membrane-associated protein containing a series of domains capable of bipolar surface orientation. |
| GO:0061761 alpha-latrotoxin receptor binding | IPI PMID:37121976 Crystal structure of LRG1 and the functional significance of... | NEW | Summary: Biochemical and cell-based experiments show glycan-state-dependent binding of human LRG1 to the alpha-latrotoxin receptor family member LPHN2. Reason: GO:0061761 specifically captures binding to an alpha-latrotoxin receptor and is more informative than generic G protein-coupled receptor or protein binding. High-affinity LPHN2 binding is strongest after deglycosylation, particularly removal of the N325 glycan; downstream angiogenic and neurotrophic assays were performed in mouse explants, so this row asserts the directly tested binding activity without generalizing those physiological outputs to humans. Supporting Evidence: PMID:37121976 In addition, our biochemical and cell-biological analyses found that the deglycosylation of LRG1, particularly the removal of glycans on N325, is critical for the high-affinity binding of LRG1 to LPHN2 and thus promotes LRG1/LPHN2-mediated angiogenic and neurotrophic processes in mouse tissue explants, even under normal glucose conditions. PMID:37121976 Recombinant human LRG1 protein and human LPHN2 variant proteins (Lec, Olf, Lec/Olf domain, or ecto-full domain) were expressed and purified as described previously20. |
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Download this section (compressed HTML)Q: Which endogenous human LRG1 glycoforms bind and activate LPHN2, where are they generated, and under which physiological or disease conditions?
Q: What receptor stoichiometry and cell-state variables determine whether LRG1 enhances ALK1-SMAD1/5 or ALK5-SMAD2 signaling?
Q: Does native human LRG1 bind human extracellular cytochrome c and neutralize a defined cytochrome-c-dependent activity in vivo?
Q: Which cellular sources of LRG1 account for its opposing net effects in normal and diabetic wound healing?
Experiment: Quantify human LRG1 binding to purified TGFBR1, TGFBR2, endoglin, ACVRL1, and TGF-beta in defined combinations by orthogonal biophysical methods; determine complex stoichiometry and structure, then test matched receptor perturbations and SMAD outputs in primary human endothelial cells and fibroblasts.
Hypothesis: Endoglin and TGF-beta jointly stabilize an LRG1-containing receptor assembly that favors endothelial ALK1-SMAD1/5 signaling, whereas a distinct assembly supports fibroblast ALK5-SMAD2 signaling.
Type: Structural biochemistry and pathway reconstitution
Experiment: Isolate LRG1 from human plasma, neutrophils, and relevant tissue fluids; map site-specific glycoforms by quantitative glycoproteomics, fractionate them, and compare LPHN1-3 binding and LPHN2-dependent signaling with recombinant native, deglycosylated, and N325-mutant controls.
Hypothesis: A discrete endogenous human LRG1 glycoform lacking or remodeling the N325 glycan is the physiologically active LPHN2 ligand.
Type: Glycoproteomics, receptor binding, and signaling assays
Experiment: Measure binding kinetics between native human LRG1 glycoforms and human cytochrome c, map the interaction interface, and test LRG1 dose-response and loss-of-function effects in human-cell assays exposed to extracellular cytochrome c before pursuing an in-vivo model.
Hypothesis: Human LRG1 recognizes human extracellular cytochrome c and changes its extracellular bioactivity or clearance.
Type: Species-matched biophysics and functional perturbation
Experiment: Combine lineage-restricted Lrg1 deletion or rescue with normal and diabetic mouse wound models, time-resolved inflammation, re-epithelialization, angiogenesis, and NETosis measurements, and validate conserved mechanisms in organotypic human skin cultures with source-specific LRG1 perturbation.
Hypothesis: Hepatic, neutrophil-derived, and local tissue LRG1 make separable contributions to normal repair and diabetes-associated NETosis and delayed wound closure.
Type: Cell-source-resolved wound model and human tissue validation
What is not known β curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The structure, stoichiometry, and cell-context determinants of the LRG1-TGF-beta receptor assembly are unresolved, including how endoglin and ligand exposure govern conditional ALK1 association and selection between ALK1-SMAD1/5 and ALK5-SMAD2 outputs.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: LRG1 directly binds isolated ALK5, TGFBR2, and endoglin ectodomains, while ALK1 association requires endoglin and is enhanced by TGF-beta1; endothelial and fibroblast assays establish distinct downstream outputs.
Significance: Defining the receptor assembly is necessary to predict when LRG1 will drive angiogenic rather than profibrotic TGF-beta signaling and to target the mechanism selectively.
What would resolve it: Determine structures and binding stoichiometries of human LRG1 with defined TGFBR1, TGFBR2, endoglin, ACVRL1, and TGF-beta combinations, then reconstitute branch-specific signaling in primary human endothelial cells and fibroblasts.
Provenance (the field's own admissions):
Gap: The physiological source, tissue distribution, and abundance of LPHN2-activating deglycosylated LRG1 in humans are unknown, as is the precise structural basis for LPHN2 selectivity over LPHN1 and LPHN3.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: Removing LRG1 glycans, especially at N325, increases LPHN2 binding, and the resulting angiogenic and neurotrophic outputs have been shown in mouse tissue explants and diabetic mouse models.
Significance: Resolving this gap will establish whether glycan-regulated LPHN2 signaling is a physiological human mechanism or primarily an experimentally induced state.
What would resolve it: Use site-resolved glycoproteomics and LPHN2-binding assays on endogenous human plasma, neutrophil, and tissue LRG1, coupled to structural analysis of a human LRG1-LPHN2 complex and receptor-paralog selectivity tests.
Provenance (the field's own admissions):
Gap: It is unknown whether human LRG1 binds human extracellular cytochrome c with physiologically relevant affinity and neutralizes cytochrome-c activity in vivo.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: Human LRG1 bound horse and snake cytochrome c, but not yeast cytochrome c, in surface-plasmon-resonance assays; independent proteome-scale screens report a human LRG1-CYCS interaction without locally accessible pair-specific assay detail.
Significance: This distinguishes a physiological extracellular damage-response function from a plausible but incompletely tested interaction.
What would resolve it: Measure binding of native human LRG1 glycoforms to human cytochrome c, map the interface, and test whether LRG1 alters extracellular cytochrome-c activity or clearance in human-cell and in-vivo models.
Provenance (the field's own admissions):
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