Affinage

MPP4

MAGUK p55 subfamily member 4 · UniProt Q96JB8

Length
637 aa
Mass
72.8 kDa
Annotated
2026-06-10
47 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge faithfulness: 4/5 claims corpus-supported (80%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

MPP4 (DLG6) is a retina-specific p55-subfamily MAGUK scaffolding protein that organizes a presynaptic protein complex at rod photoreceptor ribbon synapses to control calcium homeostasis and neurotransmitter release (PMID:11414766, PMID:17341488). It localizes to photoreceptor synaptic terminals and to the outer limiting membrane, where it is recruited into the CRB1 complex through a direct L27-domain interaction with MPP5/PALS1 (PMID:15316081, PMID:15914641). Through L27 heterodimerization MPP4 binds Veli proteins (Veli1/2/3) and PSD95beta, building a presynaptic scaffold whose assembly MPP4 nucleates (PMID:15558731, PMID:18955048). Knockout and molecular-replacement studies establish MPP4 as essential for membrane recruitment of downstream synaptic components: loss of Mpp4 removes PSD95 and plasma membrane Ca2+-ATPases (PMCAs) from presynaptic membranes, mislocalizes Veli3 and TMEM16B, enlarges synaptic ribbons consistent with elevated Ca2+, and reduces the amplitude of synaptic transmission to second-order neurons (PMID:16520334, PMID:17341488, PMID:19474308, PMID:19233278). PSD95beta specifically restores plasma membrane targeting of MPP4 and PMCA in Mpp4-mutant explants, defining an isoform-specific scaffolding requirement (PMID:19233278).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2001 Medium

    Established the molecular identity of MPP4 as a retina-restricted MAGUK, defining the domain architecture (PDZ, SH3, GUK) that would later explain its scaffolding behavior.

    Evidence Full-length cDNA cloning, sequence alignment, and genomic organization analysis

    PMID:11414766

    Open questions at the time
    • No functional or interaction data in this report
    • Cellular localization not resolved
  2. 2003 Medium

    Localized MPP4 protein to photoreceptor synaptic terminals (and connecting cilia), placing the scaffold at specific membrane-cytoskeleton compartments and restricting its action to rod synaptic terminals.

    Evidence Immunofluorescence on mammalian retina, in situ hybridization, qRT-PCR, and microarray expression analysis

    PMID:12859944 PMID:14638699

    Open questions at the time
    • No binding partners identified
    • Functional role at terminals not tested
  3. 2004 Medium

    Connected MPP4 to a defined retinal scaffold by showing its association with the CRB1 complex at the outer limiting membrane, embedding MPP4 in an established polarity/junction module.

    Evidence Co-immunoprecipitation and confocal immunohistochemistry in mouse retina

    PMID:15316081

    Open questions at the time
    • Direct versus indirect association not distinguished
    • Recruitment mechanism unknown
  4. 2005 High

    Defined the molecular mechanism of MPP4 recruitment, showing a direct MPP5/PALS1 interaction recruits MPP4 to the CRB1 complex and direct L27 heterodimerization with Veli proteins anchors it at synaptic terminals.

    Evidence Yeast two-hybrid, GST pull-down, Co-IP, in vitro L27 heterodimerization, immunoelectron microscopy, and 3D homology modeling

    PMID:15558731 PMID:15914641

    Open questions at the time
    • Stoichiometry of homo/heterodimers in vivo not resolved
    • Functional consequence of these interactions not yet tested
  5. 2006 High

    Demonstrated MPP4 is functionally required for presynaptic organization in vivo, since Mpp4 loss depletes PSD95 from presynaptic membranes and mislocalizes Veli3 without disrupting the OLM Crb complex.

    Evidence Mpp4 knockout mouse with immunohistochemistry, Western blot, ERG, and ophthalmoscopy; reciprocal Co-IP of Dlg1 complexes

    PMID:16519681 PMID:16520334

    Open questions at the time
    • Mechanism of PSD95 turnover/stabilization not defined
    • Why OLM Crb complex is spared not explained
  6. 2007 High

    Established the physiological output of the MPP4 scaffold by linking it to calcium handling, showing the complex contains PMCAs and that Mpp4 loss removes PMCAs, enlarges ribbons, and reduces synaptic transmission.

    Evidence Mpp4 knockout mouse with immunofluorescence, Co-IP, Western blot, and electroretinography

    PMID:17341488

    Open questions at the time
    • Direct measurement of presynaptic Ca2+ dynamics not performed
    • Causal chain from PMCA loss to ribbon enlargement inferred
  7. 2008 Medium

    Refined complex composition by immunoaffinity proteomics, confirming L27-mediated PSD95beta and Veli3 membership and adding recoverin and Hsc70 as associated proteins.

    Evidence Anti-MPP4 immunoaffinity chromatography, 2D electrophoresis, and mass spectrometry from retina

    PMID:18955048

    Open questions at the time
    • Roles of recoverin and Hsc70 in the complex untested
    • Direct versus indirect associations not resolved by MS
  8. 2009 High

    Extended the scaffold's recruitment role to the calcium-activated channel TMEM16B and pinned PMCA targeting to a specific PSD95beta isoform, defining MPP4 as the apical organizer of presynaptic membrane protein localization.

    Evidence MPP4-deficient mice with immunohistochemistry; lentiviral molecular replacement in retinal explants; PDZ binding motif analysis

    PMID:19233278 PMID:19474308

    Open questions at the time
    • Functional consequence of TMEM16B mislocalization on transmission not measured
    • Structural basis of PSD95beta isoform specificity unknown
  9. 2018 Low

    Placed MPP4 within transcriptional control of synapse formation by identifying it as a CRX target gene whose expression is altered in Crx-mutant retinas.

    Evidence Immunohistochemistry of Crx mutant retinas integrated with CRX/NRL ChIP-Seq and transcriptomics

    PMID:30084954

    Open questions at the time
    • No direct mechanistic experiment on MPP4 in this study
    • Direct CRX regulation of the MPP4 promoter not validated

Open questions

Synthesis pass · forward-looking unresolved questions
  • Whether MPP4 dysfunction causes human retinal disease, and how the scaffold quantitatively governs presynaptic Ca2+ dynamics and neurotransmission, remain open.
  • No timeline evidence of a causative human Mendelian mutation
  • Direct presynaptic Ca2+ imaging in Mpp4-null synapses not reported
  • Structural model of the assembled scaffold absent

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 4 GO:0008092 cytoskeletal protein binding 2
Localization
GO:0005886 plasma membrane 4 GO:0005929 cilium 1
Pathway
R-HSA-112316 Neuronal System 2
Partners
ATP2B1CRB1DLG1DLG4MPP3MPP5TMEM16BVELI3
Complex memberships
CRB1 complexMPP4 presynaptic scaffold (MPP4-PSD95beta-Veli3-PMCA-TMEM16B)

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2001 MPP4 is a retina-specific member of the p55 subfamily of MAGUK proteins, containing a single PDZ domain, SH3 domain, and guanylate kinase-like (GUK) domain, with 637 amino acids encoded by a gene on chromosome 2q31-33. Full-length cDNA cloning, sequence alignment to protein databases, genomic organization analysis Genomics Medium 11414766
2003 MPP4 protein localizes to the connecting cilia and synaptic terminals of cone and rod photoreceptors in bovine and porcine retina, suggesting roles at membrane-cytoskeleton interfaces in distinct structural and functional compartments. Immunofluorescence microscopy on mammalian retina sections using affinity-purified anti-MPP4 antibodies; Western blot of retinal extracts and transfected 293-Ebna cells Investigative ophthalmology & visual science Medium 14638699
2003 Mouse Mpp4 mRNA is expressed postnatally (not embryonically) and is exclusively localized to photoreceptor cells in the retina; Mpp4 protein localizes specifically to rod (but not cone) photoreceptor synaptic terminals. Microarray expression analysis, quantitative RT-PCR, in situ hybridization, immunofluorescence on retinal sections including cone-specific GFP transgenic mice Biochemical and biophysical research communications Medium 12859944
2004 MPP4 associates with the CRB1 protein complex at the outer limiting membrane (OLM) of the retina, co-localizing with Crb1, Mupp1, and Pals1/Mpp5. Immunohistochemistry and co-immunoprecipitation in mouse retina; confocal microscopy Journal of cell science Medium 15316081
2005 MPP4 is recruited to the CRB1 complex through direct interaction with MPP5 (PALS1); MPP4 and MPP5 co-localize at the OLM in human and mouse retina. Yeast two-hybrid and GST pull-down identified the direct MPP4–MPP5 interaction, and 3D homology modeling suggested a mechanism regulating recruitment of homo- and heterodimers of MPP4 and MPP5 to the complex. Yeast two-hybrid screening, GST pull-down assay, co-immunoprecipitation, immunohistochemistry, immunoelectron microscopy, 3D homology modeling Investigative ophthalmology & visual science High 15914641
2005 MPP4 directly interacts with Veli proteins (Veli1, Veli2, Veli3) via L27 heterodimerization in vitro, and co-localizes with Veli3 at photoreceptor synaptic terminals in the outer plexiform layer; MPP5 and MPP4 associate with Veli3 at distinct intercellular junctions in the retina. In vitro L27 heterodimerization assay, immunofluorescence microscopy, specific polyclonal and monoclonal antibody generation The Journal of comparative neurology High 15558731
2006 In Mpp4 knockout mice, Psd95 is lost from presynaptic membranes of rods and cones, and total retinal Psd95 protein levels are significantly reduced (suggesting Mpp4 is involved in Psd95 turnover). Veli3 protein levels are unchanged but its correct presynaptic localization depends on Mpp4. Loss of Mpp4 only sporadically causes photoreceptor displacement without changing the Crb complex at the OLM. Mpp4 knockout mouse analysis, immunohistochemistry, Western blot, scanning laser ophthalmoscopy, electroretinography Human molecular genetics High 16520334
2006 MPP3 and MPP4 co-localize with DLG1 at the outer plexiform layer, and mouse Dlg1 forms separate complexes with Mpp3 and Mpp4 in vivo. Co-immunoprecipitation from mouse retina, immunohistochemistry, confocal microscopy The FEBS journal Medium 16519681
2007 Mpp4 organizes a presynaptic protein complex at rod photoreceptor synaptic terminals that includes plasma membrane Ca2+-ATPases (PMCAs), Veli3, and PSD95. In Mpp4 knockout mice, PMCAs are lost from rod presynaptic membranes, synaptic ribbons are enlarged (indicative of elevated Ca2+), SERCA2 is increased, and IP3RII distribution is shifted away from synaptic terminals. Synaptic transmission to second-order neurons is maintained but reduced in amplitude. Mpp4 knockout mouse, immunofluorescence, co-immunoprecipitation, Western blot, electroretinography Human molecular genetics High 17341488
2008 Immunoaffinity purification of the MPP4-associated protein complex from retina identified: previously known components Veli3 and Psd95-beta (interaction mediated by N-terminal L27 domains of MPP4 and PSD95beta), and novel associated proteins recoverin and Hsc70. Immunoaffinity chromatography with anti-MPP4 monoclonal antibody, 2D electrophoresis, mass spectrometry Experimental eye research Medium 18955048
2009 MPP4 is required for the membrane localization of TMEM16B at photoreceptor ribbon synapses; TMEM16B is absent from photoreceptor membranes in MPP4-deficient mice. TMEM16B co-localizes with PSD95, VELI3, and MPP4 at ribbon synapses and contains a PDZ class I binding motif capable of interacting with PSD95. Immunohistochemistry and immunofluorescence in MPP4-deficient mice; co-localization analysis; PDZ binding motif analysis The Journal of neuroscience High 19474308
2009 MPP4 and PSD95beta are both essential for correct localization of PMCA at the presynaptic plasma membrane of photoreceptors. MPP4 deficiency causes loss of both PMCA and PSD95 from the photoreceptor synapse; truncation of MPP4's C-terminal part causes loss of PSD95 and mislocalization of PMCA. PSD95beta (not PSD95alpha) can restore plasma membrane localization of MPP4 and PMCA1 in Mpp4 mutant primary retinal explants. Mpp4 and Psd95 mutant mice, lentiviral molecular replacement in primary retinal explants, immunofluorescence microscopy Molecular and cellular neurosciences High 19233278
2018 CRX transcription factor controls presynaptic active zone formation in photoreceptors; MPP4 is among the CRX target genes whose expression is aberrant in Crx-mutant retinas, linking CRX-dependent transcriptional control to MPP4-containing presynaptic scaffold assembly. Immunohistochemistry of Crx mutant mouse retinas; integrated analysis with CRX- and NRL-ChIP-Seq data and retinal transcriptomics Human molecular genetics Low 30084954

Source papers

Stage 0 corpus · 47 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2004 Crumbs homologue 1 is required for maintenance of photoreceptor cell polarization and adhesion during light exposure. Journal of cell science 209 15316081
2009 TMEM16B, a novel protein with calcium-dependent chloride channel activity, associates with a presynaptic protein complex in photoreceptor terminals. The Journal of neuroscience : the official journal of the Society for Neuroscience 186 19474308
2012 Targeting of syndecan-1 by microRNA miR-10b promotes breast cancer cell motility and invasiveness via a Rho-GTPase- and E-cadherin-dependent mechanism. International journal of cancer 136 22573479
1999 DRBP76, a double-stranded RNA-binding nuclear protein, is phosphorylated by the interferon-induced protein kinase, PKR. The Journal of biological chemistry 116 10400669
2016 Progressive alterations in multipotent hematopoietic progenitors underlie lymphoid cell loss in aging. The Journal of experimental medicine 85 27811054
2004 Identification and characterization of human MPP7 gene and mouse Mpp7 gene in silico. International journal of molecular medicine 80 14719143
1999 Molecular cloning and characterization of a translational inhibitory protein that binds to coding sequences of human acid beta-glucosidase and other mRNAs. Molecular genetics and metabolism 66 10607473
2000 Alternative splicing in the human interleukin enhancer binding factor 3 (ILF3) gene. Gene 64 11167023
2005 MPP5 recruits MPP4 to the CRB1 complex in photoreceptors. Investigative ophthalmology & visual science 59 15914641
2006 Mpp4 recruits Psd95 and Veli3 towards the photoreceptor synapse. Human molecular genetics 48 16520334
2017 DNA damage tolerance in hematopoietic stem and progenitor cells in mice. Proceedings of the National Academy of Sciences of the United States of America 47 28761001
2016 Enhanced diagnostic yield in Meckel-Gruber and Joubert syndrome through exome sequencing supplemented with split-read mapping. BMC medical genetics 44 26729329
2005 Membrane-associated guanylate kinase proteins MPP4 and MPP5 associate with Veli3 at distinct intercellular junctions of the neurosensory retina. The Journal of comparative neurology 38 15558731
2023 Epigenetic programming defines haematopoietic stem cell fate restriction. Nature cell biology 33 37127714
2007 Mpp4 is required for proper localization of plasma membrane calcium ATPases and maintenance of calcium homeostasis at the rod photoreceptor synaptic terminals. Human molecular genetics 33 17341488
2000 Reconstitution of TCP80/NF90 translation inhibition activity in insect cells. Molecular genetics and metabolism 33 10873392
2021 CT based radiomic approach on first line pembrolizumab in lung cancer. Scientific reports 32 33758304
2006 MPP3 is recruited to the MPP5 protein scaffold at the retinal outer limiting membrane. The FEBS journal 32 16519681
2022 Dntt expression reveals developmental hierarchy and lineage specification of hematopoietic progenitors. Nature immunology 29 35354960
2021 Radiomics Biomarkers Correlate with CD8 Expression and Predict Immune Signatures in Melanoma Patients. Molecular cancer research : MCR 29 33811161
2017 Investigation of correlations between DNA methylation, suicidal behavior and aging. Bipolar disorders 25 28276657
2011 Comparison of proton and electron radiation effects on biological responses in liver, spleen and blood. International journal of radiation biology 24 22035456
2018 Cone-rod homeobox CRX controls presynaptic active zone formation in photoreceptors of mammalian retina. Human molecular genetics 22 30084954
2001 Cloning and characterization of the human retina-specific gene MPP4, a novel member of the p55 subfamily of MAGUK proteins. Genomics 22 11414766
2009 PSD95beta regulates plasma membrane Ca2+ pump localization at the photoreceptor synapse. Molecular and cellular neurosciences 20 19233278
2003 Cellular localization of the MPP4 protein in the mammalian retina. Investigative ophthalmology & visual science 20 14638699
2003 Cell cycle dependent intracellular distribution of two spliced isoforms of TCP/ILF3 proteins. Molecular genetics and metabolism 19 14654356
2018 A Novel Inducible Mouse Model of MLL-ENL-driven Mixed-lineage Acute Leukemia. HemaSphere 18 31723780
2013 Expression of oxidative stress and antioxidant defense genes in the kidney of inbred mice after intestinal ischemia and reperfusion. Acta cirurgica brasileira 17 24316858
2002 Characterization of MPP4, a gene highly expressed in photoreceptor cells, and mutation analysis in retinitis pigmentosa. Gene 16 12384283
2022 EBF1 primes B-lymphoid enhancers and limits the myeloid bias in murine multipotent progenitors. The Journal of experimental medicine 14 36048017
2003 Developmental and tissue expression patterns of mouse Mpp4 gene. Biochemical and biophysical research communications 13 12859944
2022 Germline ETV6 mutation promotes inflammation and disrupts lymphoid development of early hematopoietic progenitors. Experimental hematology 11 35803545
2018 A20 deficiency in multipotent progenitors perturbs quiescence of hematopoietic stem cells. Stem cell research 10 30445411
2023 Slow cycling and durable Flt3+ progenitors contribute to hematopoiesis under native conditions. The Journal of experimental medicine 8 37910046
2013 Simultaneous expression of the bacterial Dictyoglomus thermophilum xynB gene under three different Trichoderma reesei promoters. New biotechnology 8 24008227
2010 Identification of a novel peptide derived from the M-phase phosphoprotein 11 (MPP11) leukemic antigen recognized by human CD8+ cytotoxic T lymphocytes. Hematology/oncology and stem cell therapy 7 20231810
2022 Oral Trypanosoma cruzi Acute Infection in Mice Targets Primary Lymphoid Organs and Triggers Extramedullary Hematopoiesis. Frontiers in cellular and infection microbiology 5 35402296
2008 Proteomic analysis of the membrane palmitoylated protein-4 (MPP4)-associated protein complex in the retina. Experimental eye research 5 18955048
2024 CXCR4 signaling determines the fate of hematopoietic multipotent progenitors by stimulating mTOR activity and mitochondrial metabolism. Science signaling 4 39471249
2021 Lymphoid-biased hematopoietic stem cells and myeloid-biased hematopoietic progenitor cells have radioprotection activity. Blood science (Baltimore, Md.) 3 35402845
2025 Distinct transcriptional changes in hematopoietic progenitor subsets on LPS-induced emergency granulopoiesis. Experimental hematology 2 40316244
2025 Functional Comparison to Ezh2 Reveals PRC2-Independent Functions of Jarid2 in Hematopoietic Stem Cell Lineage Commitment. bioRxiv : the preprint server for biology 1 40791535
2024 WBP1L regulates hematopoietic stem cell function and T cell development. Frontiers in immunology 1 39555063
2026 Comparison with Ezh2 reveals the PRC2-dependent functions of Jarid2 in hematopoietic stem Cell lineage commitment. Stem cell reports 0 41650958
2024 An Investigation of the Inflammatory Landscape in the Brain and Bone Marrow of the APP/PS1 Mouse. Journal of Alzheimer's disease reports 0 39114548
2023 [Chronic Injury of Mice Bone Marrow Multipotent Hematopoietic Progenitor Cells Induced by Ionizing Radiation]. Zhongguo shi yan xue ye xue za zhi 0 37356954

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