Affinage

MESD

LRP chaperone MESD · UniProt Q14696

Length
234 aa
Mass
26.1 kDa
Annotated
2026-06-10
35 papers in source corpus 20 papers cited in narrative 19 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

MESD (MESDC2; Drosophila ortholog Boca) is an endoplasmic reticulum-resident specialized chaperone required for the maturation and cell-surface delivery of LDL-receptor-related proteins, and through them for canonical WNT/beta-catenin signaling and embryonic mesoderm induction (PMID:12581525, PMID:12581524). Its conserved ferredoxin-like core domain (PMID:17342452, PMID:19636811, PMID:21397184) engages the beta-propeller of newly translated LRP5/6 and related LDLR family members in the ER, holding the beta-propeller in an interaction-competent state until EGF-repeat translation produces a more mature module with lower chaperone affinity; a binding switch between a chaperone domain and an escort domain then ensures safe ER-to-Golgi trafficking by preventing premature ligand engagement (PMID:15014448, PMID:21397183). Beyond LRP5/6, MESD acts as a general LRP chaperone in vivo, required for apical LRP2/Megalin localization and visceral endoderm endocytosis (PMID:21337463), for LRP4 glycosylation, cell-surface expression, MuSK activation and neuromuscular postsynaptic specialization (PMID:24140340), and for folding and secretion of pro-alpha1(I) collagen (PMID:36526215). A C-terminal region absent in invertebrates additionally binds mature LRP5/6 at the cell surface with high affinity and antagonizes ligand binding, blocking Wnts, DKK1 and Sclerostin and thereby suppressing Wnt/beta-catenin signaling and tumor cell proliferation (PMID:16263759, PMID:20446724, PMID:23469146). ER retention of MESD is essential for its chaperone function: hypomorphic alleles and an ER-retention-signal mutation that cause MESD secretion or cytoplasmic mislocalization impair LRP5/LRP6 trafficking and collagen folding and cause autosomal-recessive osteogenesis imperfecta (PMID:31564437, PMID:36526215).

Mechanistic history

Synthesis pass · year-by-year structured walk · 15 steps
  1. 2003 High

    Established the existence of a dedicated ER chaperone for WNT co-receptors, answering how LRP5/6 reach the surface and linking this to embryonic patterning.

    Evidence Mouse knockout with developmental phenotyping and rescue, parallel Drosophila Boca loss-of-function showing trafficking defects for Arrow and Yolkless

    PMID:12581524 PMID:12581525

    Open questions at the time
    • Molecular basis of substrate recognition not yet defined
    • Domain architecture of MESD not resolved
  2. 2004 High

    Defined what MESD recognizes — the beta-propeller/EGF module — and showed the interaction is developmental/state-dependent, with affinity dropping as the module matures.

    Evidence Drosophila genetics with domain-specific maturation and protein interaction assays in the secretory pathway

    PMID:15014448

    Open questions at the time
    • Structural basis of the propeller interaction not determined
    • How maturation lowers affinity mechanistically unresolved
  3. 2004 High

    Connected MESD binding to disease-relevant LRP5 biology, showing a high-bone-mass mutation perturbs the MESD interaction and surface delivery.

    Evidence Co-IP, cell-surface expression, LRP5 domain mutagenesis and Wnt reporter assays

    PMID:15143163

    Open questions at the time
    • Whether the effect is purely chaperone-mediated or also surface antagonism unclear at this stage
  4. 2005 Low

    Suggested loss of ER targeting abolishes chaperone function, via a SENP1-MESDC2 fusion mislocalized away from the ER.

    Evidence Translocation/RT-PCR analysis and ER-targeting assay of fusion protein in tumor cells

    PMID:15917269

    Open questions at the time
    • Single case with localization only
    • Chaperone loss-of-function inferred but not directly demonstrated
  5. 2005 High

    Revealed a second, vertebrate-specific function: MESD binds mature LRP5/6 at the cell surface via its C-terminal region and antagonizes ligand binding.

    Evidence Scatchard binding analysis, co-IP, domain deletions and ligand competition assays

    PMID:16263759

    Open questions at the time
    • Physiological role of surface antagonism in normal tissue not established
    • C-terminal binding sites not yet mapped at residue level
  6. 2006 Medium

    Demonstrated MESD is rate-limiting for LRP6 folding, with dose-dependent enhancement of Wnt signaling and dominant-negative sequestration by an LRP6 mutant.

    Evidence Overexpression and Wnt reporter assays with dominant-negative LRP6

    PMID:16989816

    Open questions at the time
    • Single method set
    • Stoichiometry of chaperone-substrate complex not quantified
  7. 2007 Medium

    Provided the first structural view of the MESD core, defining its fold class.

    Evidence NMR solution structure of the conserved core (ferredoxin-like fold)

    PMID:17342452 PMID:19636811

    Open questions at the time
    • No structure of MESD bound to substrate
    • Functional residues not mapped onto the fold
  8. 2008 Medium

    Linked reduced MESD-LRP6 interaction to a skeletal phenotype, showing the ringelschwanz hypomorph impairs Wnt signaling and drives bone resorption via RANKL.

    Evidence Co-IP of LRP6 rs mutant with MESD, surface expression, Wnt reporter, RANKL and osteoclastogenesis assays

    PMID:18505367

    Open questions at the time
    • Single lab
    • Direct demonstration in patient tissue absent
  9. 2010 Medium

    Generalized the chaperone role beyond LRP5/6 in vivo (LRP2/Megalin) and established MESD as a universal LRP5/6 ligand antagonist at the surface.

    Evidence Mesd knockout with LRP2 localization/endocytosis readouts; recombinant MESD competition against DKK1/Sclerostin and Wnt reporter, LRP6 phosphorylation and proliferation assays

    PMID:20446724 PMID:21337463

    Open questions at the time
    • Full LRP substrate repertoire not enumerated
    • Surface antagonism mostly shown with recombinant/exogenous MESD
  10. 2011 High

    Resolved the two-domain mechanistic model: a chaperone domain that primes the beta-propeller and an escort domain that prevents premature ligand binding during trafficking, with structural conservation across metazoans.

    Evidence Structural analysis, domain mutagenesis, co-IP and trafficking assays; high-resolution crystal structures of three orthologs with AUC, NMR and limited proteolysis

    PMID:21397183 PMID:21397184

    Open questions at the time
    • Histidine-switch dissociation model not directly validated in cells
    • Functional role of the proposed dimer interface unconfirmed
  11. 2011 Medium

    Showed MESD blocks signaling by structurally distinct Wnt classes and suppresses tumor growth in vivo, supporting therapeutic antagonism.

    Evidence Wnt reporter assays across E1-E2 and E3-E4 binding Wnts; PC-3 xenograft model

    PMID:21907199

    Open questions at the time
    • Single lab
    • On-target specificity of antitumor effect not fully isolated
  12. 2013 Medium

    Extended substrate range to LRP4 and mapped the C-terminal surface-binding region, connecting MESD to neuromuscular junction formation and defining the antagonist peptide.

    Evidence Co-IP and glycosylation/siRNA/MuSK assays for LRP4; cell-surface binding and peptide competition mapping two basic LRP5/6 binding sites

    PMID:23469146 PMID:24140340

    Open questions at the time
    • In vivo NMJ requirement not tested in this work
    • Residue-level structural basis of C-terminal binding not solved
  13. 2019 Medium

    Established that ER retention—not chaperone competence per se—is the function lost in disease, defining the molecular lesion in autosomal-recessive OI.

    Evidence Whole exome sequencing plus expression of WT/mutant MESD with lysate-vs-medium Western blot and LRP5 chaperoning assays

    PMID:31564437

    Open questions at the time
    • Single lab
    • In vivo skeletal consequence not modeled
  14. 2022 Medium

    Identified pro-alpha1(I) collagen as a direct MESD substrate and showed an ER-retention mutation drives proteostatic collapse, mechanistically unifying WNT and collagen defects in OI.

    Evidence Whole exome sequencing, MESD-COL1A1 co-IP, immunofluorescence, WNT target gene and adhesion assays in patient fibroblasts

    PMID:36526215

    Open questions at the time
    • Single lab
    • Whether collagen and LRP chaperoning use the same domain not dissected
  15. 2016 Low

    Raised the possibility of an extracellular MESD function in phagocytic clearance of shed photoreceptor outer segments by RPE cells.

    Evidence Phagocytosis and selective binding assays with POS vesicles and Rab7 colocalization in primary RPE cells

    PMID:27184668

    Open questions at the time
    • RPE receptor for MESD not identified
    • Single lab with limited mechanistic follow-up
    • Relationship to ER chaperone role unclear

Open questions

Synthesis pass · forward-looking unresolved questions
  • How a single ER chaperone partitions between intracellular folding/escort of diverse LRP and collagen substrates and a vertebrate-specific extracellular antagonist role, and the structural basis of substrate-specific recognition, remain unresolved.
  • No co-structure of MESD with any substrate
  • Determinants selecting among LRP2/4/5/6 and collagen substrates unknown
  • Mechanism and partners of extracellular MESD undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0044183 protein folding chaperone 5 GO:0098772 molecular function regulator activity 3 GO:0140096 catalytic activity, acting on a protein 3
Localization
GO:0005783 endoplasmic reticulum 5 GO:0005886 plasma membrane 3 GO:0005576 extracellular region 2
Pathway
R-HSA-162582 Signal Transduction 4 R-HSA-1266738 Developmental Biology 3 R-HSA-392499 Metabolism of proteins 3 R-HSA-1643685 Disease 2
Partners
COL1A1LRP2LRP4LRP5LRP6

Evidence

Reading pass · 19 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 MESD functions in the endoplasmic reticulum as a specific chaperone for LRP5 and LRP6, which are coreceptors for canonical WNT signal transduction; loss of MESD disrupts embryonic polarity and mesoderm induction in mice. Genetic knockout mouse model, phenotypic analysis, in vivo functional rescue experiments Cell High 12581525
2003 Boca (Drosophila ortholog of MESD) is an ER protein specifically required for intracellular trafficking of LDL receptor family members Arrow (required for Wingless signaling) and Yolkless (required for yolk protein uptake), establishing Boca as an essential component of the Wingless pathway. Drosophila genetic loss-of-function, cell biological trafficking assays Cell High 12581524
2004 Boca/MESD is specifically required for maturation of beta-propeller/EGF domain modules through the secretory pathway; it binds to the beta-propeller as LDLRs are translated into the ER, and after EGF repeat translation the beta-propeller/EGF module achieves a more mature state with lower affinity for Boca. Drosophila genetics, protein interaction assays, domain-specific maturation assays in the secretory pathway The EMBO journal High 15014448
2004 The LRP5 high-bone-mass G171V mutation disrupts LRP5 interaction with MESD, resulting in fewer LRP5 molecules on the cell surface, because the third YWTD repeat domain (not the first) is required for DKK1-mediated antagonism. Co-immunoprecipitation, cell surface expression assays, mutagenesis of LRP5 domains, Wnt signaling reporter assays Molecular and cellular biology High 15143163
2005 MESD binds to cell surface LRP5 and LRP6 (but not other LDLR family members) with high affinity (Kd ~3.3 nM for LRP6); the C-terminal region of MESD (absent in invertebrates) is necessary and sufficient for binding to mature LRP6 and is also required for LRP6 folding; MESD antagonizes ligand binding to LRP6 at the cell surface. Scatchard binding analysis, co-immunoprecipitation, domain deletion mutants, cell surface binding assays, ligand competition assays Journal of cell science High 16263759
2006 MESD overexpression enhances LRP6-mediated Wnt signaling in a dose-dependent manner by promoting LRP6 folding and maturation to the cell surface; an LRP6 mutant lacking the intracellular domain acts dominantly negative by sequestering MESD from promoting LRP6 folding. Overexpression experiments, Wnt signaling reporter assays, dominant-negative LRP6 mutant analysis FEBS letters Medium 16989816
2007 NMR solution structure of the conserved core of MESD (residues 104–177 / MESD(12-155)) reveals a four-stranded anti-parallel beta-sheet with two alpha-helices, adopting a ferrodoxin-like fold with a novel secondary structure connectivity. NMR spectroscopy (15N-HSQC, full spectral assignment), solution structure determination Journal of structural and functional genomics / Biomolecular NMR assignments Medium 17342452 19636811
2008 The Lrp6 ringelschwanz (rs) hypomorphic mutation causes decreased targeting of LRP6 to the plasma membrane due to reduced interaction with MESD, leading to impaired Wnt/beta-catenin signaling and increased RANKL expression in osteoblasts, resulting in enhanced bone resorption. Co-immunoprecipitation (LRP6 rs mutant vs MESD), cell surface expression assays, Wnt/beta-catenin reporter assays, RANKL expression analysis, osteoclastogenesis assays Journal of bone and mineral research Medium 18505367
2010 Recombinant MESD binds to mature LRP5 with high affinity at the cell surface and acts as a universal inhibitor of LRP5 and LRP6 ligands, blocking binding of Wnt antagonists DKK1 and Sclerostin to LRP5/6, inhibiting Wnt3A- and Rspondin1-induced Wnt/beta-catenin signaling, suppressing LRP6 phosphorylation in prostate cancer PC-3 cells, and inhibiting PC-3 cell proliferation. Cell surface binding assays, ligand competition assays (Mesd vs DKK1, Sclerostin), Wnt/beta-catenin reporter assays, LRP6 phosphorylation assays, cell proliferation assays Biochemistry Medium 20446724
2010 MESD is essential for apical localization of LRP2 (Megalin/MEG) in the visceral endoderm; loss of MESD impairs endocytic function of visceral endoderm cells, and MESD functions as a general LRP chaperone in vivo beyond LRP5/6. Targeted Mesd knockout mouse, immunofluorescence localization of LRP2, endocytic function assays in visceral endoderm Developmental dynamics Medium 21337463
2011 MESD contains two structural domains: a chaperone domain that forms a complex with immature LRP5/6, maintaining the beta-propeller domain in an interaction-competent state for EGF-repeat binding to promote proper folding (causing a binding switch from chaperone domain to escort domain); and an escort domain that ensures safe trafficking of LRP5/6 from ER to Golgi by preventing premature ligand-binding; a histidine switch in the beta-propeller domain may regulate MESD dissociation and retrieval in the Golgi. Structural analysis, domain mutagenesis, co-immunoprecipitation, cell biological trafficking assays, biochemical folding assays Structure High 21397183
2011 X-ray crystallography of Boca/MESD orthologs from three metazoans reveals a conserved core with a novel ferrodoxin-like superfamily fold with two distinct beta-sheet topologies; a conserved hydrophobic surface forms a dimer interface that may play a role in chaperone activity. X-ray crystallography (high-resolution structures of three metazoan orthologs), NMR spectroscopy, analytical ultracentrifugation, limited proteolysis Structure High 21397184
2011 Recombinant MESD protein inhibits Wnt/beta-catenin signaling induced by both LRP6 E1-E2-binding Wnts and E3-E4-binding Wnts, and suppresses tumor growth in a PC-3 xenograft model in vivo. Wnt/beta-catenin reporter assays, PC-3 xenograft tumor model in mice FEBS letters Medium 21907199
2013 MESDC2 binds to the intracellular form of LRP4 and promotes its glycosylation and cell-surface expression; knockdown of Mesdc2 suppresses cell-surface expression of LRP4, activation of MuSK, and postsynaptic specialization in muscle cells, establishing a role for MESDC2 in neuromuscular junction formation. Co-immunoprecipitation (Mesdc2-LRP4), glycosylation assays, siRNA knockdown, MuSK activation assays, postsynaptic specialization assays in myotubes FEBS letters Medium 24140340
2013 The C-terminal region of MESD constitutes the major LRP5/6-binding domain at the cell surface and contains two LRP5/6 binding sites with positively charged residues; C-terminal peptides block Wnt3A- and Rspondin1-induced signaling and inhibit cancer cell proliferation. Cell surface binding assays, peptide competition assays, Wnt signaling reporter assays, cell proliferation assays, cytotoxicity assays PloS one Medium 23469146
2019 Autosomal-recessive OI-associated MESD mutations are hypomorphic alleles occurring downstream of the chaperone activity domain but upstream of the ER-retention domain; wild-type MESD is retained in cell lysate while mutant MESD is secreted into conditioned medium; both WT and mutant MESD retain the ability to chaperone LRP5, but failure to remain in the ER significantly reduces LRP5 and LRP6 trafficking. Whole exome sequencing, HEK293T expression of WT and mutant MESD, Western blot of cell lysate vs conditioned medium, LRP5 chaperoning assay American journal of human genetics Medium 31564437
2022 MESD is a direct chaperone of pro-α1(I) collagen (COL1A1) in addition to LRP5/6; a D233N mutation in the ER retention signal of MESD causes mislocalization to the cytoplasm, leading to imbalanced ER proteostasis, improper folding and aggregation of both LRP5 and type I collagen, loss of LRP5 plasma membrane localization, reduced WNT-responsive gene expression (BMP2, BMP4), decreased secreted type I collagen, blockade of intercellular nanotubes, and reduced ITGB1-collagen interaction. Whole exome sequencing, co-immunoprecipitation (MESD-COL1A1), immunofluorescence localization, WNT target gene expression analysis, autophagy assays, fibroblast adhesion assays Matrix biology Medium 36526215
2016 Extracellularly released MESD selectively binds to shed photoreceptor outer segment (POS) vesicles and apoptotic cells (but not healthy cells), binds to unknown phagocytic receptor(s) on retinal pigment epithelial (RPE) cells, and promotes phagocytic clearance of POSs by RPE cells; internalized POSs colocalize with phagosome marker Rab7. Phagocytosis assay with fluorescent POS vesicles, co-localization with Rab7, selective binding assays to POS vs healthy cells, RPE primary cell assays Cell biology and toxicology Low 27184668
2005 A chromosomal translocation fusing SENP1 and MESDC2 produces a SEME fusion protein that is no longer targeted to the ER, resulting in presumed loss of chaperone function for WNT co-receptors LRP5/LRP6. Chromosomal translocation analysis, RT-PCR of fusion transcripts, ER targeting assay of fusion protein in tumor-derived cells Human molecular genetics Low 15917269

Source papers

Stage 0 corpus · 35 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2003 Mesd encodes an LRP5/6 chaperone essential for specification of mouse embryonic polarity. Cell 211 12581525
2004 The LRP5 high-bone-mass G171V mutation disrupts LRP5 interaction with Mesd. Molecular and cellular biology 135 15143163
2003 Boca, an endoplasmic reticulum protein required for wingless signaling and trafficking of LDL receptor family members in Drosophila. Cell 122 12581524
2009 Detection of a novel porcine boca-like virus in the background of porcine circovirus type 2 induced postweaning multisystemic wasting syndrome. Virus research 121 19748534
1995 Prediction of the coding sequences of unidentified human genes. III. The coding sequences of 40 new genes (KIAA0081-KIAA0120) deduced by analysis of cDNA clones from human cell line KG-1. DNA research : an international journal for rapid publication of reports on genes and genomes 92 7788527
2015 A 1-Year Quantitative Survey of Noro-, Adeno-, Human Boca-, and Hepatitis E Viruses in Raw and Secondarily Treated Sewage from Two Plants in Norway. Food and environmental virology 60 26003323
2008 Lrp6 hypomorphic mutation affects bone mass through bone resorption in mice and impairs interaction with Mesd. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research 60 18505367
2019 Autosomal-Recessive Mutations in MESD Cause Osteogenesis Imperfecta. American journal of human genetics 47 31564437
2010 Mesd is a universal inhibitor of Wnt coreceptors LRP5 and LRP6 and blocks Wnt/beta-catenin signaling in cancer cells. Biochemistry 46 20446724
2005 Mesd binds to mature LDL-receptor-related protein-6 and antagonizes ligand binding. Journal of cell science 45 16263759
2004 Boca-dependent maturation of beta-propeller/EGF modules in low-density lipoprotein receptor proteins. The EMBO journal 44 15014448
2011 Mesd is a general inhibitor of different Wnt ligands in Wnt/LRP signaling and inhibits PC-3 tumor growth in vivo. FEBS letters 35 21907199
2013 Inhibition of LRP5/6-mediated Wnt/β-catenin signaling by Mesd attenuates hyperoxia-induced pulmonary hypertension in neonatal rats. Pediatric research 31 23481549
2005 Fusion of the SUMO/Sentrin-specific protease 1 gene SENP1 and the embryonic polarity-related mesoderm development gene MESDC2 in a patient with an infantile teratoma and a constitutional t(12;15)(q13;q25). Human molecular genetics 23 15917269
2022 Mutant MESD links cellular stress to type I collagen aggregation in osteogenesis imperfecta type XX. Matrix biology : journal of the International Society for Matrix Biology 20 36526215
2011 Development of a novel TaqMan-based real-time PCR assay for the detection of porcine boca-like virus (Pbo-likeV). Virology journal 20 21771316
2006 Modulation of LRP6-mediated Wnt signaling by molecular chaperone Mesd. FEBS letters 20 16989816
2001 In Southern Africa, brown oculocutaneous albinism (BOCA) maps to the OCA2 locus on chromosome 15q: P-gene mutations identified. American journal of human genetics 20 11179026
2013 Mesdc2 plays a key role in cell-surface expression of Lrp4 and postsynaptic specialization in myotubes. FEBS letters 17 24140340
2011 Two structural and functional domains of MESD required for proper folding and trafficking of LRP5/6. Structure (London, England : 1993) 17 21397183
2010 MESD is essential for apical localization of megalin/LRP2 in the visceral endoderm. Developmental dynamics : an official publication of the American Association of Anatomists 15 21337463
2001 Identification of mesoderm development (mesd) candidate genes by comparative mapping and genome sequence analysis. Genomics 15 11247670
2013 The C-terminal region Mesd peptide mimics full-length Mesd and acts as an inhibitor of Wnt/β-catenin signaling in cancer cells. PloS one 14 23469146
2021 Compound Heterozygous Frameshift Mutations in MESD Cause a Lethal Syndrome Suggestive of Osteogenesis Imperfecta Type XX. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research 13 33596325
2016 Assessment of pollution of the Boca de Camichin Estuary in Nayarit (Mexico) and its influence on oxidative stress in Crassostrea corteziensis oysters. Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 9 27156678
2011 Structural characterization of the Boca/Mesd maturation factors for LDL-receptor-type β propeller domains. Structure (London, England : 1993) 9 21397184
2007 A complete NMR spectral assignment of the conserved region of the MESD protein, MESD(12-155). Biomolecular NMR assignments 9 19636811
2021 Biallelic variants in MESD, which encodes a WNT-signaling-related protein, in four new families with recessively inherited osteogenesis imperfecta. HGG advances 8 35047842
2007 The solution structure of the core of mesoderm development (MESD), a chaperone for members of the LDLR-family. Journal of structural and functional genomics 7 17342452
2000 Physical localization of the mesoderm development (mesd) functional region. Genomics 5 10995574
2016 Mesd extrinsically promotes phagocytosis by retinal pigment epithelial cells. Cell biology and toxicology 4 27184668
2011 The RNA profile of porcine parvovirus 4, a boca-like virus, is unique among the parvoviruses. Archives of virology 3 21785854
2023 Detection of Human Boca Virus in Gastric Adenocarcinoma. Middle East journal of digestive diseases 2 38023466
2025 Evaluating the cross-reactivity of a stool methylated syndecan-2 (meSDC2) test in colorectal cancer detection. Journal of gastrointestinal oncology 1 41220757
2013 Development of a conditional Mesd (mesoderm development) allele for functional analysis of the low-density lipoprotein receptor-related family in defined tissues. PloS one 1 24124512

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