cadA

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005509 calcium ion binding	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetic inference of calcium ion binding is well supported by direct experimental evidence for DdCAD-1. The protein carries multiple Ca2+-binding sites and calcium is required for its adhesion and its import into contractile vacuoles. Reason: Calcium binding is a genuine and central property of DdCAD-1, demonstrated directly by 45Ca2+ overlay and NMR structures, so the IBA inference is corroborated by experimental data. Supporting Evidence: PMID:8227052 Binding studies showed that 45Ca2+ could bind to gp24 blotted onto nitrocellulose membrane
GO:0005516 calmodulin binding	IBA GO_REF:0000033	ACCEPT	Summary: Calmodulin binding by DdCAD-1 is supported by direct experimental evidence. Ca2+-bound calmodulin interacts with DdCAD-1 and promotes its import into contractile vacuoles. Reason: Co-immunoprecipitation and pull-down assays demonstrate a direct DdCAD-1 / Ca2+-calmodulin interaction, corroborating the phylogenetic inference. Supporting Evidence: PMID:23441816 Co-immunoprecipitation and pull-down studies showed that only Ca(2+) -bound calmodulin was able to bind DdCAD-1
GO:0005911 cell-cell junction	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: DdCAD-1 concentrates at cell-cell contact regions during early development, so a broad cell-cell junction assignment is defensible, but Dictyostelium adhesion sites are not classic junctions and this is not the most informative descriptor of the protein's activity. Reason: DdCAD-1 is enriched in cell contact regions, but the core statement of its function is captured by external side of plasma membrane and calcium-dependent cell-cell adhesion; the junction term is retained as a non-core localization. Supporting Evidence: PMID:8806827 A high concentration of DdCAD-1 also becomes associated with lamellipodia and filopodia, which often appear to participate in cell contact formation
GO:0009897 external side of plasma membrane	IBA GO_REF:0000033	ACCEPT	Summary: DdCAD-1 acts on the ecto-surface of the plasma membrane, where it mediates homophilic adhesion. This is directly supported by immunofluorescence and is a core localization. Reason: The phylogenetic inference matches direct experimental evidence that DdCAD-1 is associated with the outer face of the plasma membrane. Supporting Evidence: PMID:8663243 immunofluorescence microscopy demonstrates the association of DdCAD-1 with the ecto-surface of the plasma membrane
GO:0016339 calcium-dependent cell-cell adhesion	IBA GO_REF:0000033	ACCEPT	Summary: This is the defining function of DdCAD-1, strongly supported by biochemical and genetic evidence. It mediates the EDTA/EGTA-sensitive calcium-dependent adhesion of the early developmental stage. Reason: Calcium-dependent homophilic cell-cell adhesion is the core evolved function of DdCAD-1 and is directly demonstrated experimentally. Supporting Evidence: PMID:8227052 It is therefore likely that gp24 mediates cell-cell interactions via a Ca(2+)-dependent mechanism
GO:0005886 plasma membrane	IEA GO_REF:0000044	ACCEPT	Summary: DdCAD-1 is presented on the plasma membrane after transport by contractile vacuoles. Plasma membrane localization is well supported. Reason: The UniProt-derived location matches direct evidence that DdCAD-1 is transported to and anchored at the plasma membrane. Supporting Evidence: PMID:17057715 It is synthesized as a soluble protein and then transported to the plasma membrane by contractile vacuoles
GO:0016020 membrane	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: The generic membrane term is subsumed by the more specific and experimentally supported plasma membrane and external side of plasma membrane annotations. Reason: The generic membrane term is an uninformative parent of the specific plasma membrane localization already annotated for DdCAD-1; it adds no information.
GO:0098609 cell-cell adhesion	IEA GO_REF:0000002	MODIFY	Summary: The general cell-cell adhesion term is correct but a more specific child term, calcium-dependent cell-cell adhesion, precisely captures the DdCAD-1 mechanism and is already annotated with experimental support. Reason: DdCAD-1 mediates specifically calcium-dependent (EDTA/EGTA-sensitive) cell-cell adhesion; the more specific term should replace the generic one. Proposed replacements: calcium-dependent cell-cell adhesion Supporting Evidence: PMID:8227052 It is therefore likely that gp24 mediates cell-cell interactions via a Ca(2+)-dependent mechanism
GO:0005515 protein binding	IPI PMID:23441816 Ca(2+) -calmodulin interacts with DdCAD-1 and promotes DdCAD...	MODIFY	Summary: This IPI records the DdCAD-1 / calmodulin interaction. The bare protein binding term is uninformative; the specific partner is calmodulin, already annotated as calmodulin binding. Reason: The interacting partner in this reference is Ca2+-calmodulin, so the more informative molecular function calmodulin binding should be used instead of generic protein binding. Proposed replacements: calmodulin binding Supporting Evidence: PMID:23441816 the data show that calmodulin forms a complex with DdCAD-1 and promotes the docking and import of DdCAD-1 into contractile vacuoles
GO:0042802 identical protein binding	IPI PMID:17057715 Solution structures of the adhesion molecule DdCAD-1 reveal ...	ACCEPT	Summary: DdCAD-1 self-associates to form a Ca2+-bound homodimer, the molecular basis of its homophilic adhesion. Identical protein binding correctly captures this self-interaction. Reason: NMR structural analysis supports a DdCAD-1 dimer model underlying homophilic cell-cell adhesion, directly justifying identical protein binding. Supporting Evidence: PMID:17057715 we propose a model for the Ca(2+)-bound DdCAD-1 dimer as a basis for understanding DdCAD-1-mediated cell-cell adhesion
GO:0071944 cell periphery	IDA PMID:38986731 Trafficking of adhesion and aggregation-modulating proteins ...	ACCEPT	Summary: DdCAD-1 localizes to the cell periphery in growth-phase and starved cells, consistent with its role as a surface adhesion molecule. Reason: Direct localization evidence places CadA at the cell periphery; this is a correct, if general, localization. Supporting Evidence: PMID:38986731 As for CadA, it localizes to the cell periphery in growth-phase and starved cells
GO:0005516 calmodulin binding	IPI PMID:23441816 Ca(2+) -calmodulin interacts with DdCAD-1 and promotes DdCAD...	ACCEPT	Summary: Direct co-immunoprecipitation and pull-down evidence shows DdCAD-1 binds Ca2+-calmodulin, an interaction that promotes its docking and import into contractile vacuoles. Reason: Calmodulin binding is directly demonstrated and is functionally relevant to the unconventional secretion of DdCAD-1. Supporting Evidence: PMID:23441816 Co-immunoprecipitation and pull-down studies showed that only Ca(2+) -bound calmodulin was able to bind DdCAD-1
GO:0031012 extracellular matrix	IDA PMID:26152465 Proteomic profiling of the extracellular matrix (slime sheat...	KEEP AS NON CORE	Summary: DdCAD-1 was detected by LC/MS/MS in the slug extracellular matrix (slime sheath). Because DdCAD-1 is a secreted protein, its presence in the ECM is plausible but is a secondary localization rather than its core site of action. Reason: Proteomic detection in the slime sheath is consistent with DdCAD-1 being unconventionally secreted, but the ECM is not where it performs its core homophilic adhesion function. Supporting Evidence: PMID:26152465 An LC/MS/MS analysis of slug ECM revealed the presence of a large number of proteins in two wild-type strains, NC4 and WS380B
GO:0000331 contractile vacuole	IDA PMID:19875452 Cell adhesion molecule DdCAD-1 is imported into contractile ...	ACCEPT	Summary: DdCAD-1 is imported into contractile vacuoles by membrane invagination and transported to the plasma membrane. This is a core, well-established localization central to its unconventional secretion. Reason: Both in vivo time-lapse imaging and in vitro reconstitution demonstrate DdCAD-1 import into contractile vacuoles. Supporting Evidence: PMID:19875452 Both morphological and biochemical characterizations showed that DdCAD-1-GFP was imported into contractile vacuoles
GO:0000331 contractile vacuole	IDA PMID:9265658 The cell adhesion molecule DdCAD-1 in Dictyostelium is targe...	ACCEPT	Summary: Immunofluorescence and subcellular fractionation show preferential association of DdCAD-1 with contractile vacuoles, the organelle that transports it to the cell surface. Reason: This foundational study established contractile vacuoles as the transport route for DdCAD-1, a core localization. Supporting Evidence: PMID:9265658 Immunofluorescence microscopy and subcellular fractionation revealed a preferential association of DdCAD-1 with contractile vacuoles
GO:0001726 ruffle	IDA PMID:8806827 Novel redistribution of the Ca(2+)-dependent cell adhesion m...	KEEP AS NON CORE	Summary: During redistribution before aggregation, DdCAD-1 becomes enriched on membrane ruffles. This is a dynamic, developmental-stage-specific localization rather than a core site of function. Reason: Enrichment on membrane ruffles is directly observed but reflects the protein's redistribution to the cell surface, not a distinct core function. Supporting Evidence: PMID:8806827 DdCAD-1 become localized predominantly at the cell periphery and an enrichment of DdCAD-1 occurs on membrane ruffles
GO:0005576 extracellular region	IDA PMID:31355329 Social amoebae establish a protective interface with their b...	ACCEPT	Summary: Secreted CadA acts extracellularly as a bacterial agglutinin at the plaque edge. Its activity in the extracellular region is directly demonstrated in the bacterial defense context. Reason: Recombinant CadA secreted/deposited extracellularly agglutinates bacteria and protects amoebae, establishing a genuine extracellular site of action. Supporting Evidence: PMID:31355329 CadA, a cell adhesion protein that functions in D. discoideum development, is also a bacterial agglutinin that forms a protective interface at the plaque edge that limits exposure of vegetative amoebae to bacteria
GO:0005737 cytoplasm	IDA PMID:19875452 Cell adhesion molecule DdCAD-1 is imported into contractile ...	ACCEPT	Summary: DdCAD-1 is synthesized as a soluble cytoplasmic protein before being imported into contractile vacuoles. Cytoplasmic localization is a core part of its biosynthesis and trafficking. Reason: DdCAD-1 lacks a signal peptide and is made as a soluble cytosolic protein, directly documented in this study. Supporting Evidence: PMID:19875452 DdCAD-1 is synthesized in the cytoplasm as a soluble protein and then transported by contractile vacuoles to the plasma membrane for surface presentation or secretion
GO:0005737 cytoplasm	IDA PMID:8663243 Molecular cloning and characterization of DdCAD-1, a Ca2+-de...	ACCEPT	Summary: The founding studies place a large fraction of DdCAD-1 in the cytosol, consistent with its lack of a signal peptide. Reason: Cytoplasmic (cytosolic) localization of soluble DdCAD-1 is well-established and forms part of its normal life cycle. Supporting Evidence: PMID:9265658 DdCAD-1 is present on the cell surface as well as in the cytosol
GO:0005811 lipid droplet	HDA PMID:24036346 Dictyostelium lipid droplets host novel proteins.	MARK AS OVER ANNOTATED	Summary: This assignment comes from a high-throughput proteomic survey of purified lipid droplets. The study focused on novel lipid droplet proteins and DdCAD-1 is an abundant soluble/secreted protein prone to co-purifying as a contaminant. Lipid droplet residence is not consistent with DdCAD-1 biology. Reason: A large-scale organelle proteomics hit is a weak basis for localization of an abundant secreted adhesion molecule; there is no functional rationale for DdCAD-1 in lipid droplets. Supporting Evidence: PMID:24036346 to further identify the lipid constituents and proteins of lipid droplets
GO:0005938 cell cortex	TAS PMID:15366765 Comparison of molecular mechanisms mediating cell contact ph...	KEEP AS NON CORE	Summary: A traceable author statement from a comparative review places DdCAD-1 at the cell cortex/periphery. This is consistent with its surface localization but is a general descriptor. Reason: Cortical/peripheral localization overlaps with the better-supported external side of plasma membrane and cell periphery annotations and is retained as non-core.
GO:0009897 external side of plasma membrane	IDA PMID:8663243 Molecular cloning and characterization of DdCAD-1, a Ca2+-de...	ACCEPT	Summary: Direct immunofluorescence shows DdCAD-1 on the ecto-surface of the plasma membrane, its principal functional location for homophilic adhesion. Reason: This is a core localization directly demonstrated by the founding characterization of DdCAD-1. Supporting Evidence: PMID:8663243 immunofluorescence microscopy demonstrates the association of DdCAD-1 with the ecto-surface of the plasma membrane
GO:0030027 lamellipodium	IDA PMID:8806827 Novel redistribution of the Ca(2+)-dependent cell adhesion m...	KEEP AS NON CORE	Summary: DdCAD-1 becomes concentrated on lamellipodia during the redistribution that precedes aggregation, where these structures form cell contacts. Reason: This is a dynamic developmental localization reflecting surface redistribution rather than a separate core function. Supporting Evidence: PMID:8806827 A high concentration of DdCAD-1 also becomes associated with lamellipodia and filopodia, which often appear to participate in cell contact formation
GO:0030139 endocytic vesicle	IDA PMID:7593293 Identification of major proteins associated with Dictyosteli...	MARK AS OVER ANNOTATED	Summary: This assignment derives from a proteomic catalog of magnetically isolated endocytic vesicles that reported the major protein constituents, including a 25 kDa ORF product. DdCAD-1 is an abundant protein and its appearance in such preparations is most likely incidental rather than functional. Reason: Detection in a bulk endocytic-vesicle proteome does not establish a functional role or stable residence for DdCAD-1 in endocytic vesicles. Supporting Evidence: PMID:7593293 This strategy allowed the identification of the major protein constituents of the vesicles
GO:0030175 filopodium	IDA PMID:8806827 Novel redistribution of the Ca(2+)-dependent cell adhesion m...	KEEP AS NON CORE	Summary: DdCAD-1 concentrates on filopodia that participate in early cell contact formation, a dynamic developmental localization. Reason: Filopodial enrichment reflects the surface redistribution of DdCAD-1 during aggregation rather than a distinct core function. Supporting Evidence: PMID:8806827 A high concentration of DdCAD-1 also becomes associated with lamellipodia and filopodia, which often appear to participate in cell contact formation
GO:0045335 phagocytic vesicle	HDA PMID:16926386 Proteomics fingerprinting of phagosome maturation and eviden...	MARK AS OVER ANNOTATED	Summary: This comes from a large-scale two-dimensional gel / mass spectrometry survey that identified 179 phagosomal proteins. DdCAD-1 is not a phagosomal component by function, and its detection in this catalog is most plausibly a co-purification artifact. Reason: High-throughput phagosome proteomics is a weak basis for asserting functional phagocytic vesicle localization of an abundant secreted adhesion molecule. Supporting Evidence: PMID:16926386 we identified 179 phagosomal proteins in the amoeba Dictyostelium
GO:0045335 phagocytic vesicle	HDA PMID:19482547 Proteomic analysis of Legionella-containing phagosomes isola...	MARK AS OVER ANNOTATED	Summary: This assignment derives from a proteomic survey of Legionella-containing phagosomes that identified 157 host proteins. DdCAD-1's appearance is most likely incidental co-purification rather than a functional localization. Reason: A bulk phagosome proteome hit does not establish a functional role for DdCAD-1 in phagocytic vesicles. Supporting Evidence: PMID:19482547 identified 157 phagosome host proteins
GO:0016339 calcium-dependent cell-cell adhesion	IMP PMID:12135922 Disruption of the gene encoding the cell adhesion molecule D...	ACCEPT	Summary: Disruption of cadA reduces EDTA-sensitive (calcium-dependent) cell adhesion by ~50%, providing genetic (loss-of-function) evidence for the core adhesion function of DdCAD-1. Reason: The cadA-null phenotype directly demonstrates DdCAD-1's requirement for calcium-dependent cell-cell adhesion; this is a core function. Supporting Evidence: PMID:12135922 The cadA-null cells showed a 50% reduction in EDTA-sensitive cell adhesion
GO:0005886 plasma membrane	IDA PMID:17057715 Solution structures of the adhesion molecule DdCAD-1 reveal ...	ACCEPT	Summary: DdCAD-1 is transported to and functions at the plasma membrane, where its C-terminal domain tethers it to a membrane anchor while the N-terminal domain mediates homophilic binding. Reason: Plasma membrane is a core functional location for DdCAD-1, supported by structural and localization studies. Supporting Evidence: PMID:17057715 Whereas the N-terminal domain has a major role in homophilic binding, the C-terminal domain tethers the protein to the cell membrane
GO:0005911 cell-cell junction	IDA PMID:8663243 Molecular cloning and characterization of DdCAD-1, a Ca2+-de...	KEEP AS NON CORE	Summary: DdCAD-1 acts at cell-cell contact regions during early development. Dictyostelium adhesion sites are not classic junctions, so this term is retained as a supporting, non-core descriptor. Reason: The more precise statement of DdCAD-1 activity is external side of plasma membrane plus calcium-dependent cell-cell adhesion; the junction term is a general localization. Supporting Evidence: PMID:8663243 immunofluorescence microscopy demonstrates the association of DdCAD-1 with the ecto-surface of the plasma membrane
GO:0007157 heterophilic cell-cell adhesion	IDA PMID:31355329 Social amoebae establish a protective interface with their b...	KEEP AS NON CORE	Summary: This annotation reflects CadA's calcium- and galactose-dependent agglutination of Gram-negative bacteria (binding a non-self bacterial surface). The classic DdCAD-1 amoebal adhesion is homophilic; this heterophilic activity is a distinct lectin-mediated, non-core role. Reason: The heterophilic binding here is CadA binding bacterial surface carbohydrates rather than amoeba-amoeba adhesion; it is a genuine but secondary (moonlighting) function captured more mechanistically by carbohydrate binding. Supporting Evidence: PMID:31355329 This suggests that CadA is a lectin that binds to carbohydrates on the surface of K. pneumoniae, perhaps to their lipopolysaccharide, which is rich in galactose moieties
GO:0016339 calcium-dependent cell-cell adhesion	IGI PMID:16622066 An activated Ras protein alters cell adhesion by dephosphory...	ACCEPT	Summary: Genetic interaction with RasG modulates DdCAD-1-dependent cohesion; activated RasG increases DdCAD-1 surface localization and calcium-dependent cell adhesion. Supports the core adhesion function. Reason: The RasG-dependent change in cohesion is DdCAD-1-dependent, reinforcing DdCAD-1's role in calcium-dependent cell-cell adhesion. Supporting Evidence: PMID:16622066 This increased cohesion was DdCAD-1-dependent and was correlated with increased localization of DdCAD-1 at the cell surface
GO:0031152 aggregation involved in sorocarp development	TAS PMID:15366765 Comparison of molecular mechanisms mediating cell contact ph...	KEEP AS NON CORE	Summary: DdCAD-1 mediates the earliest adhesive contacts that enable aggregation at the onset of development. Its involvement in aggregation is a downstream developmental consequence of its adhesion activity. Reason: Aggregation is a developmental process DdCAD-1 contributes to via its core adhesion function; retained as a non-core process annotation.
GO:0050829 defense response to Gram-negative bacterium	IMP PMID:31355329 Social amoebae establish a protective interface with their b...	KEEP AS NON CORE	Summary: cadA-null amoebae have strongly reduced viability on dense lawns of Klebsiella pneumoniae, and secreted CadA agglutinates the bacteria and protects amoebae from their toxicity. This is a well-supported but secondary (moonlighting) function distinct from developmental adhesion. Reason: The bacterial-defense role is genuine and directly demonstrated by loss-of-function and rescue experiments, but it is a separate, non-core function from the protein's developmental cell-adhesion role. Supporting Evidence: PMID:31355329 This interface is important for amoebal survival when bacteria-to-amoebae ratios are high
GO:0051702 biological process involved in interaction with symbiont	IDA PMID:31355329 Social amoebae establish a protective interface with their b...	KEEP AS NON CORE	Summary: Secreted CadA binds and agglutinates associated bacteria, imposing structure on the bacterial population at the plaque edge. This captures the same bacterial-interaction moonlighting role. Reason: CadA's direct interaction with bacterial associates is documented, but it is a secondary function relative to its developmental adhesion role. Supporting Evidence: PMID:31355329 CadA, a cell adhesion protein that functions in D. discoideum development, is also a bacterial agglutinin that forms a protective interface at the plaque edge that limits exposure of vegetative amoebae to bacteria
GO:0005515 protein binding	IPI PMID:24426151 ATP-Binding Cassette Transporter B4 Anchors the Cell Adhesio...	KEEP AS NON CORE	Summary: This IPI records the interaction between DdCAD-1 and its plasma membrane anchor, identified by cross-linking and mass spectrometry as the ABC transporter ABCB4. The bare protein binding term is uninformative but no specific molecular-function term captures the anchoring interaction. Reason: The interaction with the ABCB4 anchor is real and functionally relevant to surface presentation, but generic protein binding is not a core molecular function; retained as non-core rather than as core adhesion machinery. Supporting Evidence: PMID:24426151 to identify ABCB4 as the anchor protein of DdCAD-1
GO:0005509 calcium ion binding	IDA PMID:17057715 Solution structures of the adhesion molecule DdCAD-1 reveal ...	ACCEPT	Summary: NMR solution structures of Ca2+-free and Ca2+-bound DdCAD-1 directly demonstrate calcium binding, which is required for adhesion and for contractile-vacuole import. A core molecular function. Reason: Structural determination of the Ca2+-bound form provides direct evidence for calcium ion binding by DdCAD-1. Supporting Evidence: PMID:17057715 we propose a model for the Ca(2+)-bound DdCAD-1 dimer as a basis for understanding DdCAD-1-mediated cell-cell adhesion
GO:0005509 calcium ion binding	IDA PMID:8227052 Characterization of the cell adhesion molecule gp24 in Dicty...	ACCEPT	Summary: 45Ca2+ overlay assays and calcium-induced gel-mobility shifts directly demonstrate that DdCAD-1 (gp24) is a calcium-binding protein. A core molecular function. Reason: Direct 45Ca2+ binding to gp24 establishes calcium ion binding as an intrinsic property of DdCAD-1. Supporting Evidence: PMID:8227052 Binding studies showed that 45Ca2+ could bind to gp24 blotted onto nitrocellulose membrane
GO:1904643 response to curcumin	IDA PMID:26449461 Curcumin inhibits development and cell adhesion in Dictyoste...	KEEP AS NON CORE	Summary: This annotation stems from the observation that curcumin treatment suppresses expression of DdCAD (and csA) and delays adhesion. This makes DdCAD a target affected by curcumin rather than a protein with a functional role in a curcumin response. Reason: The evidence shows DdCAD expression is down-regulated by curcumin, an indirect drug effect; it is at best a peripheral process annotation, not a core function. Supporting Evidence: PMID:26449461 expression of the extracellular matrix/cell adhesion proteins (DdCAD and csA)
GO:0010468 regulation of gene expression	IDA PMID:12135922 Disruption of the gene encoding the cell adhesion molecule D...	UNDECIDED	Summary: The cadA-null study documents altered cell-type proportioning (increased prestalk proportion) and aberrant sorting, but the cached abstract does not describe a direct role for DdCAD-1 in regulating gene expression, and full text was not available for verification. Reason: The relevant publication is available only as an abstract, which does not substantiate a molecular role in regulation of gene expression; the documented phenotype is adhesion-driven cell sorting and proportioning. Per policy this experimental annotation is left undecided pending full-text verification rather than removed.
GO:0030587 sorocarp development	IMP PMID:12135922 Disruption of the gene encoding the cell adhesion molecule D...	KEEP AS NON CORE	Summary: cadA-null cells complete development but show abnormal slug morphology, delayed culmination, reduced spore yield, and altered cell-type proportioning, implicating DdCAD-1 in normal fruiting-body development. Reason: DdCAD-1 contributes to sorocarp development through its adhesion and cell-sorting activities; a genuine developmental role but downstream of its core molecular function. Supporting Evidence: PMID:12135922 These results indicate that, in addition to cell-cell adhesion, DdCAD-1 plays a role in cell type proportioning and pattern formation
GO:0031288 sorocarp morphogenesis	IMP PMID:21561987 The cell adhesion molecule DdCAD-1 regulates morphogenesis t...	KEEP AS NON CORE	Summary: Differential spatiotemporal distribution of DdCAD-1 on prestalk versus prespore cells governs cell sorting in slugs, contributing to morphogenesis of the fruiting body. Reason: DdCAD-1 influences morphogenesis via differential adhesion and sorting; a developmental role downstream of its core adhesion function. Supporting Evidence: PMID:21561987 These results show that DdCAD-1 influences the sorting behavior of cells in slugs by its differential distribution on the prestalk and prespore cells
GO:0016339 calcium-dependent cell-cell adhesion	IDA PMID:17057715 Solution structures of the adhesion molecule DdCAD-1 reveal ...	ACCEPT	Summary: Structural and mutational analyses define the Ca2+-bound DdCAD-1 dimer as the molecular basis of calcium-dependent cell-cell adhesion, the core function of the protein. Reason: Direct structural evidence links calcium binding and homophilic dimerization to DdCAD-1-mediated calcium-dependent cell-cell adhesion. Supporting Evidence: PMID:17057715 Our results provide new insights into Ca(2+)-dependent mechanisms for cell-cell adhesion

📄 View Raw YAML

id: P54657
gene_symbol: cadA
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:44689
  label: Dictyostelium discoideum
description: DdCAD-1 (also called gp24 or CadA) is the calcium-dependent
  (EDTA/EGTA-sensitive) homophilic cell-cell adhesion molecule of the social
  amoeba Dictyostelium discoideum. It is a 24 kDa, 213-residue protein composed
  of two beta-sandwich domains (an N-terminal betagamma-crystallin-like domain
  and a C-terminal immunoglobulin-like domain); the N-terminal domain mediates
  homophilic binding whereas the C-terminal domain tethers the protein to the
  plasma membrane. DdCAD-1 is a soluble calcium-binding protein that lacks a
  signal peptide and a transmembrane domain; it is synthesized in the cytoplasm
  at the onset of starvation-induced development and reaches the cell surface by
  an unconventional secretion route in which it is imported into and transported
  by contractile vacuoles and then anchored to the plasma membrane by the ABC
  transporter ABCB4. Calcium binding and association with calmodulin are required
  for its import into contractile vacuoles. On the cell surface it establishes
  the earliest (contact-site-B) adhesions that drive aggregation, and its
  differential distribution between prestalk and prespore cells contributes to
  cell sorting, cell-type proportioning, and morphogenesis of the fruiting body
  (sorocarp). Independently of development, secreted DdCAD-1 also acts as a
  calcium-dependent, galactose-specific lectin that agglutinates Gram-negative
  bacteria such as Klebsiella pneumoniae, forming a protective interface that
  shields feeding amoebae from bacterial toxicity.
existing_annotations:
- term:
    id: GO:0005509
    label: calcium ion binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: Phylogenetic inference of calcium ion binding is well supported by
      direct experimental evidence for DdCAD-1. The protein carries multiple
      Ca2+-binding sites and calcium is required for its adhesion and its import
      into contractile vacuoles.
    action: ACCEPT
    reason: Calcium binding is a genuine and central property of DdCAD-1,
      demonstrated directly by 45Ca2+ overlay and NMR structures, so the IBA
      inference is corroborated by experimental data.
    supported_by:
    - reference_id: PMID:8227052
      supporting_text: Binding studies showed that 45Ca2+ could bind to gp24
        blotted onto nitrocellulose membrane
- term:
    id: GO:0005516
    label: calmodulin binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: Calmodulin binding by DdCAD-1 is supported by direct experimental
      evidence. Ca2+-bound calmodulin interacts with DdCAD-1 and promotes its
      import into contractile vacuoles.
    action: ACCEPT
    reason: Co-immunoprecipitation and pull-down assays demonstrate a direct
      DdCAD-1 / Ca2+-calmodulin interaction, corroborating the phylogenetic
      inference.
    supported_by:
    - reference_id: PMID:23441816
      supporting_text: Co-immunoprecipitation and pull-down studies showed that
        only Ca(2+) -bound calmodulin was able to bind DdCAD-1
- term:
    id: GO:0005911
    label: cell-cell junction
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: DdCAD-1 concentrates at cell-cell contact regions during early
      development, so a broad cell-cell junction assignment is defensible, but
      Dictyostelium adhesion sites are not classic junctions and this is not the
      most informative descriptor of the protein's activity.
    action: KEEP_AS_NON_CORE
    reason: DdCAD-1 is enriched in cell contact regions, but the core statement
      of its function is captured by external side of plasma membrane and
      calcium-dependent cell-cell adhesion; the junction term is retained as a
      non-core localization.
    supported_by:
    - reference_id: PMID:8806827
      supporting_text: A high concentration of DdCAD-1 also becomes associated
        with lamellipodia and filopodia, which often appear to participate in
        cell contact formation
- term:
    id: GO:0009897
    label: external side of plasma membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: DdCAD-1 acts on the ecto-surface of the plasma membrane, where it
      mediates homophilic adhesion. This is directly supported by
      immunofluorescence and is a core localization.
    action: ACCEPT
    reason: The phylogenetic inference matches direct experimental evidence that
      DdCAD-1 is associated with the outer face of the plasma membrane.
    supported_by:
    - reference_id: PMID:8663243
      supporting_text: immunofluorescence microscopy demonstrates the association
        of DdCAD-1 with the ecto-surface of the plasma membrane
- term:
    id: GO:0016339
    label: calcium-dependent cell-cell adhesion
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: This is the defining function of DdCAD-1, strongly supported by
      biochemical and genetic evidence. It mediates the EDTA/EGTA-sensitive
      calcium-dependent adhesion of the early developmental stage.
    action: ACCEPT
    reason: Calcium-dependent homophilic cell-cell adhesion is the core evolved
      function of DdCAD-1 and is directly demonstrated experimentally.
    supported_by:
    - reference_id: PMID:8227052
      supporting_text: It is therefore likely that gp24 mediates cell-cell
        interactions via a Ca(2+)-dependent mechanism
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: DdCAD-1 is presented on the plasma membrane after transport by
      contractile vacuoles. Plasma membrane localization is well supported.
    action: ACCEPT
    reason: The UniProt-derived location matches direct evidence that DdCAD-1 is
      transported to and anchored at the plasma membrane.
    supported_by:
    - reference_id: PMID:17057715
      supporting_text: It is synthesized as a soluble protein and then
        transported to the plasma membrane by contractile vacuoles
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: located_in
  review:
    summary: The generic membrane term is subsumed by the more specific and
      experimentally supported plasma membrane and external side of plasma
      membrane annotations.
    action: MARK_AS_OVER_ANNOTATED
    reason: The generic membrane term is an uninformative parent of the specific
      plasma membrane localization already annotated for DdCAD-1; it adds no
      information.
- term:
    id: GO:0098609
    label: cell-cell adhesion
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: The general cell-cell adhesion term is correct but a more specific
      child term, calcium-dependent cell-cell adhesion, precisely captures the
      DdCAD-1 mechanism and is already annotated with experimental support.
    action: MODIFY
    reason: DdCAD-1 mediates specifically calcium-dependent (EDTA/EGTA-sensitive)
      cell-cell adhesion; the more specific term should replace the generic one.
    proposed_replacement_terms:
    - id: GO:0016339
      label: calcium-dependent cell-cell adhesion
    supported_by:
    - reference_id: PMID:8227052
      supporting_text: It is therefore likely that gp24 mediates cell-cell
        interactions via a Ca(2+)-dependent mechanism
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:23441816
  qualifier: enables
  review:
    summary: This IPI records the DdCAD-1 / calmodulin interaction. The bare
      protein binding term is uninformative; the specific partner is calmodulin,
      already annotated as calmodulin binding.
    action: MODIFY
    reason: The interacting partner in this reference is Ca2+-calmodulin, so the
      more informative molecular function calmodulin binding should be used
      instead of generic protein binding.
    proposed_replacement_terms:
    - id: GO:0005516
      label: calmodulin binding
    supported_by:
    - reference_id: PMID:23441816
      supporting_text: the data show that calmodulin forms a complex with
        DdCAD-1 and promotes the docking and import of DdCAD-1 into contractile
        vacuoles
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:17057715
  qualifier: enables
  review:
    summary: DdCAD-1 self-associates to form a Ca2+-bound homodimer, the
      molecular basis of its homophilic adhesion. Identical protein binding
      correctly captures this self-interaction.
    action: ACCEPT
    reason: NMR structural analysis supports a DdCAD-1 dimer model underlying
      homophilic cell-cell adhesion, directly justifying identical protein
      binding.
    supported_by:
    - reference_id: PMID:17057715
      supporting_text: we propose a model for the Ca(2+)-bound DdCAD-1 dimer as a
        basis for understanding DdCAD-1-mediated cell-cell adhesion
- term:
    id: GO:0071944
    label: cell periphery
  evidence_type: IDA
  original_reference_id: PMID:38986731
  qualifier: located_in
  review:
    summary: DdCAD-1 localizes to the cell periphery in growth-phase and starved
      cells, consistent with its role as a surface adhesion molecule.
    action: ACCEPT
    reason: Direct localization evidence places CadA at the cell periphery; this
      is a correct, if general, localization.
    supported_by:
    - reference_id: PMID:38986731
      supporting_text: As for CadA, it localizes to the cell periphery in
        growth-phase and starved cells
- term:
    id: GO:0005516
    label: calmodulin binding
  evidence_type: IPI
  original_reference_id: PMID:23441816
  qualifier: enables
  review:
    summary: Direct co-immunoprecipitation and pull-down evidence shows DdCAD-1
      binds Ca2+-calmodulin, an interaction that promotes its docking and import
      into contractile vacuoles.
    action: ACCEPT
    reason: Calmodulin binding is directly demonstrated and is functionally
      relevant to the unconventional secretion of DdCAD-1.
    supported_by:
    - reference_id: PMID:23441816
      supporting_text: Co-immunoprecipitation and pull-down studies showed that
        only Ca(2+) -bound calmodulin was able to bind DdCAD-1
- term:
    id: GO:0031012
    label: extracellular matrix
  evidence_type: IDA
  original_reference_id: PMID:26152465
  qualifier: located_in
  review:
    summary: DdCAD-1 was detected by LC/MS/MS in the slug extracellular matrix
      (slime sheath). Because DdCAD-1 is a secreted protein, its presence in the
      ECM is plausible but is a secondary localization rather than its core site
      of action.
    action: KEEP_AS_NON_CORE
    reason: Proteomic detection in the slime sheath is consistent with DdCAD-1
      being unconventionally secreted, but the ECM is not where it performs its
      core homophilic adhesion function.
    supported_by:
    - reference_id: PMID:26152465
      supporting_text: An LC/MS/MS analysis of slug ECM revealed the presence of
        a large number of proteins in two wild-type strains, NC4 and WS380B
- term:
    id: GO:0000331
    label: contractile vacuole
  evidence_type: IDA
  original_reference_id: PMID:19875452
  qualifier: located_in
  review:
    summary: DdCAD-1 is imported into contractile vacuoles by membrane
      invagination and transported to the plasma membrane. This is a core,
      well-established localization central to its unconventional secretion.
    action: ACCEPT
    reason: Both in vivo time-lapse imaging and in vitro reconstitution
      demonstrate DdCAD-1 import into contractile vacuoles.
    supported_by:
    - reference_id: PMID:19875452
      supporting_text: Both morphological and biochemical characterizations
        showed that DdCAD-1-GFP was imported into contractile vacuoles
- term:
    id: GO:0000331
    label: contractile vacuole
  evidence_type: IDA
  original_reference_id: PMID:9265658
  qualifier: located_in
  review:
    summary: Immunofluorescence and subcellular fractionation show preferential
      association of DdCAD-1 with contractile vacuoles, the organelle that
      transports it to the cell surface.
    action: ACCEPT
    reason: This foundational study established contractile vacuoles as the
      transport route for DdCAD-1, a core localization.
    supported_by:
    - reference_id: PMID:9265658
      supporting_text: Immunofluorescence microscopy and subcellular
        fractionation revealed a preferential association of DdCAD-1 with
        contractile vacuoles
- term:
    id: GO:0001726
    label: ruffle
  evidence_type: IDA
  original_reference_id: PMID:8806827
  qualifier: located_in
  review:
    summary: During redistribution before aggregation, DdCAD-1 becomes enriched
      on membrane ruffles. This is a dynamic, developmental-stage-specific
      localization rather than a core site of function.
    action: KEEP_AS_NON_CORE
    reason: Enrichment on membrane ruffles is directly observed but reflects the
      protein's redistribution to the cell surface, not a distinct core function.
    supported_by:
    - reference_id: PMID:8806827
      supporting_text: DdCAD-1 become localized predominantly at the cell
        periphery and an enrichment of DdCAD-1 occurs on membrane ruffles
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IDA
  original_reference_id: PMID:31355329
  qualifier: is_active_in
  review:
    summary: Secreted CadA acts extracellularly as a bacterial agglutinin at the
      plaque edge. Its activity in the extracellular region is directly
      demonstrated in the bacterial defense context.
    action: ACCEPT
    reason: Recombinant CadA secreted/deposited extracellularly agglutinates
      bacteria and protects amoebae, establishing a genuine extracellular site of
      action.
    supported_by:
    - reference_id: PMID:31355329
      supporting_text: CadA, a cell adhesion protein that functions in D.
        discoideum development, is also a bacterial agglutinin that forms a
        protective interface at the plaque edge that limits exposure of
        vegetative amoebae to bacteria
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:19875452
  qualifier: located_in
  review:
    summary: DdCAD-1 is synthesized as a soluble cytoplasmic protein before being
      imported into contractile vacuoles. Cytoplasmic localization is a core part
      of its biosynthesis and trafficking.
    action: ACCEPT
    reason: DdCAD-1 lacks a signal peptide and is made as a soluble cytosolic
      protein, directly documented in this study.
    supported_by:
    - reference_id: PMID:19875452
      supporting_text: DdCAD-1 is synthesized in the cytoplasm as a soluble
        protein and then transported by contractile vacuoles to the plasma
        membrane for surface presentation or secretion
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:8663243
  qualifier: located_in
  review:
    summary: The founding studies place a large fraction of DdCAD-1 in the
      cytosol, consistent with its lack of a signal peptide.
    action: ACCEPT
    reason: Cytoplasmic (cytosolic) localization of soluble DdCAD-1 is
      well-established and forms part of its normal life cycle.
    supported_by:
    - reference_id: PMID:9265658
      supporting_text: DdCAD-1 is present on the cell surface as well as in the
        cytosol
- term:
    id: GO:0005811
    label: lipid droplet
  evidence_type: HDA
  original_reference_id: PMID:24036346
  qualifier: located_in
  review:
    summary: This assignment comes from a high-throughput proteomic survey of
      purified lipid droplets. The study focused on novel lipid droplet proteins
      and DdCAD-1 is an abundant soluble/secreted protein prone to co-purifying
      as a contaminant. Lipid droplet residence is not consistent with DdCAD-1
      biology.
    action: MARK_AS_OVER_ANNOTATED
    reason: A large-scale organelle proteomics hit is a weak basis for
      localization of an abundant secreted adhesion molecule; there is no
      functional rationale for DdCAD-1 in lipid droplets.
    supported_by:
    - reference_id: PMID:24036346
      supporting_text: to further identify the lipid constituents and proteins of
        lipid droplets
- term:
    id: GO:0005938
    label: cell cortex
  evidence_type: TAS
  original_reference_id: PMID:15366765
  qualifier: located_in
  review:
    summary: A traceable author statement from a comparative review places
      DdCAD-1 at the cell cortex/periphery. This is consistent with its surface
      localization but is a general descriptor.
    action: KEEP_AS_NON_CORE
    reason: Cortical/peripheral localization overlaps with the better-supported
      external side of plasma membrane and cell periphery annotations and is
      retained as non-core.
- term:
    id: GO:0009897
    label: external side of plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:8663243
  qualifier: is_active_in
  review:
    summary: Direct immunofluorescence shows DdCAD-1 on the ecto-surface of the
      plasma membrane, its principal functional location for homophilic adhesion.
    action: ACCEPT
    reason: This is a core localization directly demonstrated by the founding
      characterization of DdCAD-1.
    supported_by:
    - reference_id: PMID:8663243
      supporting_text: immunofluorescence microscopy demonstrates the association
        of DdCAD-1 with the ecto-surface of the plasma membrane
- term:
    id: GO:0030027
    label: lamellipodium
  evidence_type: IDA
  original_reference_id: PMID:8806827
  qualifier: located_in
  review:
    summary: DdCAD-1 becomes concentrated on lamellipodia during the
      redistribution that precedes aggregation, where these structures form cell
      contacts.
    action: KEEP_AS_NON_CORE
    reason: This is a dynamic developmental localization reflecting surface
      redistribution rather than a separate core function.
    supported_by:
    - reference_id: PMID:8806827
      supporting_text: A high concentration of DdCAD-1 also becomes associated
        with lamellipodia and filopodia, which often appear to participate in
        cell contact formation
- term:
    id: GO:0030139
    label: endocytic vesicle
  evidence_type: IDA
  original_reference_id: PMID:7593293
  qualifier: located_in
  review:
    summary: This assignment derives from a proteomic catalog of magnetically
      isolated endocytic vesicles that reported the major protein constituents,
      including a 25 kDa ORF product. DdCAD-1 is an abundant protein and its
      appearance in such preparations is most likely incidental rather than
      functional.
    action: MARK_AS_OVER_ANNOTATED
    reason: Detection in a bulk endocytic-vesicle proteome does not establish a
      functional role or stable residence for DdCAD-1 in endocytic vesicles.
    supported_by:
    - reference_id: PMID:7593293
      supporting_text: This strategy allowed the identification of the major
        protein constituents of the vesicles
- term:
    id: GO:0030175
    label: filopodium
  evidence_type: IDA
  original_reference_id: PMID:8806827
  qualifier: is_active_in
  review:
    summary: DdCAD-1 concentrates on filopodia that participate in early cell
      contact formation, a dynamic developmental localization.
    action: KEEP_AS_NON_CORE
    reason: Filopodial enrichment reflects the surface redistribution of DdCAD-1
      during aggregation rather than a distinct core function.
    supported_by:
    - reference_id: PMID:8806827
      supporting_text: A high concentration of DdCAD-1 also becomes associated
        with lamellipodia and filopodia, which often appear to participate in
        cell contact formation
- term:
    id: GO:0045335
    label: phagocytic vesicle
  evidence_type: HDA
  original_reference_id: PMID:16926386
  qualifier: located_in
  review:
    summary: This comes from a large-scale two-dimensional gel / mass
      spectrometry survey that identified 179 phagosomal proteins. DdCAD-1 is not
      a phagosomal component by function, and its detection in this catalog is
      most plausibly a co-purification artifact.
    action: MARK_AS_OVER_ANNOTATED
    reason: High-throughput phagosome proteomics is a weak basis for asserting
      functional phagocytic vesicle localization of an abundant secreted adhesion
      molecule.
    supported_by:
    - reference_id: PMID:16926386
      supporting_text: we identified 179 phagosomal proteins in the amoeba
        Dictyostelium
- term:
    id: GO:0045335
    label: phagocytic vesicle
  evidence_type: HDA
  original_reference_id: PMID:19482547
  qualifier: located_in
  review:
    summary: This assignment derives from a proteomic survey of
      Legionella-containing phagosomes that identified 157 host proteins.
      DdCAD-1's appearance is most likely incidental co-purification rather than
      a functional localization.
    action: MARK_AS_OVER_ANNOTATED
    reason: A bulk phagosome proteome hit does not establish a functional role
      for DdCAD-1 in phagocytic vesicles.
    supported_by:
    - reference_id: PMID:19482547
      supporting_text: identified 157 phagosome host proteins
- term:
    id: GO:0016339
    label: calcium-dependent cell-cell adhesion
  evidence_type: IMP
  original_reference_id: PMID:12135922
  qualifier: involved_in
  review:
    summary: Disruption of cadA reduces EDTA-sensitive (calcium-dependent) cell
      adhesion by ~50%, providing genetic (loss-of-function) evidence for the
      core adhesion function of DdCAD-1.
    action: ACCEPT
    reason: The cadA-null phenotype directly demonstrates DdCAD-1's requirement
      for calcium-dependent cell-cell adhesion; this is a core function.
    supported_by:
    - reference_id: PMID:12135922
      supporting_text: The cadA-null cells showed a 50% reduction in
        EDTA-sensitive cell adhesion
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:17057715
  qualifier: is_active_in
  review:
    summary: DdCAD-1 is transported to and functions at the plasma membrane,
      where its C-terminal domain tethers it to a membrane anchor while the
      N-terminal domain mediates homophilic binding.
    action: ACCEPT
    reason: Plasma membrane is a core functional location for DdCAD-1, supported
      by structural and localization studies.
    supported_by:
    - reference_id: PMID:17057715
      supporting_text: Whereas the N-terminal domain has a major role in
        homophilic binding, the C-terminal domain tethers the protein to the cell
        membrane
- term:
    id: GO:0005911
    label: cell-cell junction
  evidence_type: IDA
  original_reference_id: PMID:8663243
  qualifier: is_active_in
  review:
    summary: DdCAD-1 acts at cell-cell contact regions during early development.
      Dictyostelium adhesion sites are not classic junctions, so this term is
      retained as a supporting, non-core descriptor.
    action: KEEP_AS_NON_CORE
    reason: The more precise statement of DdCAD-1 activity is external side of
      plasma membrane plus calcium-dependent cell-cell adhesion; the junction
      term is a general localization.
    supported_by:
    - reference_id: PMID:8663243
      supporting_text: immunofluorescence microscopy demonstrates the association
        of DdCAD-1 with the ecto-surface of the plasma membrane
- term:
    id: GO:0007157
    label: heterophilic cell-cell adhesion
  evidence_type: IDA
  original_reference_id: PMID:31355329
  qualifier: involved_in
  review:
    summary: This annotation reflects CadA's calcium- and galactose-dependent
      agglutination of Gram-negative bacteria (binding a non-self bacterial
      surface). The classic DdCAD-1 amoebal adhesion is homophilic; this
      heterophilic activity is a distinct lectin-mediated, non-core role.
    action: KEEP_AS_NON_CORE
    reason: The heterophilic binding here is CadA binding bacterial surface
      carbohydrates rather than amoeba-amoeba adhesion; it is a genuine but
      secondary (moonlighting) function captured more mechanistically by
      carbohydrate binding.
    supported_by:
    - reference_id: PMID:31355329
      supporting_text: This suggests that CadA is a lectin that binds to
        carbohydrates on the surface of K. pneumoniae, perhaps to their
        lipopolysaccharide, which is rich in galactose moieties
- term:
    id: GO:0016339
    label: calcium-dependent cell-cell adhesion
  evidence_type: IGI
  original_reference_id: PMID:16622066
  qualifier: involved_in
  review:
    summary: Genetic interaction with RasG modulates DdCAD-1-dependent cohesion;
      activated RasG increases DdCAD-1 surface localization and calcium-dependent
      cell adhesion. Supports the core adhesion function.
    action: ACCEPT
    reason: The RasG-dependent change in cohesion is DdCAD-1-dependent,
      reinforcing DdCAD-1's role in calcium-dependent cell-cell adhesion.
    supported_by:
    - reference_id: PMID:16622066
      supporting_text: This increased cohesion was DdCAD-1-dependent and was
        correlated with increased localization of DdCAD-1 at the cell surface
- term:
    id: GO:0031152
    label: aggregation involved in sorocarp development
  evidence_type: TAS
  original_reference_id: PMID:15366765
  qualifier: acts_upstream_of_or_within
  review:
    summary: DdCAD-1 mediates the earliest adhesive contacts that enable
      aggregation at the onset of development. Its involvement in aggregation is
      a downstream developmental consequence of its adhesion activity.
    action: KEEP_AS_NON_CORE
    reason: Aggregation is a developmental process DdCAD-1 contributes to via its
      core adhesion function; retained as a non-core process annotation.
- term:
    id: GO:0050829
    label: defense response to Gram-negative bacterium
  evidence_type: IMP
  original_reference_id: PMID:31355329
  qualifier: acts_upstream_of_or_within
  review:
    summary: cadA-null amoebae have strongly reduced viability on dense lawns of
      Klebsiella pneumoniae, and secreted CadA agglutinates the bacteria and
      protects amoebae from their toxicity. This is a well-supported but
      secondary (moonlighting) function distinct from developmental adhesion.
    action: KEEP_AS_NON_CORE
    reason: The bacterial-defense role is genuine and directly demonstrated by
      loss-of-function and rescue experiments, but it is a separate, non-core
      function from the protein's developmental cell-adhesion role.
    supported_by:
    - reference_id: PMID:31355329
      supporting_text: This interface is important for amoebal survival when
        bacteria-to-amoebae ratios are high
- term:
    id: GO:0051702
    label: biological process involved in interaction with symbiont
  evidence_type: IDA
  original_reference_id: PMID:31355329
  qualifier: acts_upstream_of_or_within
  review:
    summary: Secreted CadA binds and agglutinates associated bacteria, imposing
      structure on the bacterial population at the plaque edge. This captures the
      same bacterial-interaction moonlighting role.
    action: KEEP_AS_NON_CORE
    reason: CadA's direct interaction with bacterial associates is documented,
      but it is a secondary function relative to its developmental adhesion role.
    supported_by:
    - reference_id: PMID:31355329
      supporting_text: CadA, a cell adhesion protein that functions in D.
        discoideum development, is also a bacterial agglutinin that forms a
        protective interface at the plaque edge that limits exposure of
        vegetative amoebae to bacteria
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:24426151
  qualifier: enables
  review:
    summary: This IPI records the interaction between DdCAD-1 and its plasma
      membrane anchor, identified by cross-linking and mass spectrometry as the
      ABC transporter ABCB4. The bare protein binding term is uninformative but
      no specific molecular-function term captures the anchoring interaction.
    action: KEEP_AS_NON_CORE
    reason: The interaction with the ABCB4 anchor is real and functionally
      relevant to surface presentation, but generic protein binding is not a core
      molecular function; retained as non-core rather than as core adhesion
      machinery.
    supported_by:
    - reference_id: PMID:24426151
      supporting_text: to identify ABCB4 as the anchor protein of DdCAD-1
- term:
    id: GO:0005509
    label: calcium ion binding
  evidence_type: IDA
  original_reference_id: PMID:17057715
  qualifier: enables
  review:
    summary: NMR solution structures of Ca2+-free and Ca2+-bound DdCAD-1 directly
      demonstrate calcium binding, which is required for adhesion and for
      contractile-vacuole import. A core molecular function.
    action: ACCEPT
    reason: Structural determination of the Ca2+-bound form provides direct
      evidence for calcium ion binding by DdCAD-1.
    supported_by:
    - reference_id: PMID:17057715
      supporting_text: we propose a model for the Ca(2+)-bound DdCAD-1 dimer as a
        basis for understanding DdCAD-1-mediated cell-cell adhesion
- term:
    id: GO:0005509
    label: calcium ion binding
  evidence_type: IDA
  original_reference_id: PMID:8227052
  qualifier: enables
  review:
    summary: 45Ca2+ overlay assays and calcium-induced gel-mobility shifts
      directly demonstrate that DdCAD-1 (gp24) is a calcium-binding protein. A
      core molecular function.
    action: ACCEPT
    reason: Direct 45Ca2+ binding to gp24 establishes calcium ion binding as an
      intrinsic property of DdCAD-1.
    supported_by:
    - reference_id: PMID:8227052
      supporting_text: Binding studies showed that 45Ca2+ could bind to gp24
        blotted onto nitrocellulose membrane
- term:
    id: GO:1904643
    label: response to curcumin
  evidence_type: IDA
  original_reference_id: PMID:26449461
  qualifier: involved_in
  review:
    summary: This annotation stems from the observation that curcumin treatment
      suppresses expression of DdCAD (and csA) and delays adhesion. This makes
      DdCAD a target affected by curcumin rather than a protein with a functional
      role in a curcumin response.
    action: KEEP_AS_NON_CORE
    reason: The evidence shows DdCAD expression is down-regulated by curcumin, an
      indirect drug effect; it is at best a peripheral process annotation, not a
      core function.
    supported_by:
    - reference_id: PMID:26449461
      supporting_text: expression of the extracellular matrix/cell adhesion
        proteins (DdCAD and csA)
- term:
    id: GO:0010468
    label: regulation of gene expression
  evidence_type: IDA
  original_reference_id: PMID:12135922
  qualifier: involved_in
  review:
    summary: The cadA-null study documents altered cell-type proportioning
      (increased prestalk proportion) and aberrant sorting, but the cached
      abstract does not describe a direct role for DdCAD-1 in regulating gene
      expression, and full text was not available for verification.
    action: UNDECIDED
    reason: The relevant publication is available only as an abstract, which does
      not substantiate a molecular role in regulation of gene expression; the
      documented phenotype is adhesion-driven cell sorting and proportioning.
      Per policy this experimental annotation is left undecided pending full-text
      verification rather than removed.
- term:
    id: GO:0030587
    label: sorocarp development
  evidence_type: IMP
  original_reference_id: PMID:12135922
  qualifier: acts_upstream_of_or_within
  review:
    summary: cadA-null cells complete development but show abnormal slug
      morphology, delayed culmination, reduced spore yield, and altered cell-type
      proportioning, implicating DdCAD-1 in normal fruiting-body development.
    action: KEEP_AS_NON_CORE
    reason: DdCAD-1 contributes to sorocarp development through its adhesion and
      cell-sorting activities; a genuine developmental role but downstream of its
      core molecular function.
    supported_by:
    - reference_id: PMID:12135922
      supporting_text: These results indicate that, in addition to cell-cell
        adhesion, DdCAD-1 plays a role in cell type proportioning and pattern
        formation
- term:
    id: GO:0031288
    label: sorocarp morphogenesis
  evidence_type: IMP
  original_reference_id: PMID:21561987
  qualifier: acts_upstream_of_or_within
  review:
    summary: Differential spatiotemporal distribution of DdCAD-1 on prestalk
      versus prespore cells governs cell sorting in slugs, contributing to
      morphogenesis of the fruiting body.
    action: KEEP_AS_NON_CORE
    reason: DdCAD-1 influences morphogenesis via differential adhesion and
      sorting; a developmental role downstream of its core adhesion function.
    supported_by:
    - reference_id: PMID:21561987
      supporting_text: These results show that DdCAD-1 influences the sorting
        behavior of cells in slugs by its differential distribution on the
        prestalk and prespore cells
- term:
    id: GO:0016339
    label: calcium-dependent cell-cell adhesion
  evidence_type: IDA
  original_reference_id: PMID:17057715
  qualifier: involved_in
  review:
    summary: Structural and mutational analyses define the Ca2+-bound DdCAD-1
      dimer as the molecular basis of calcium-dependent cell-cell adhesion, the
      core function of the protein.
    action: ACCEPT
    reason: Direct structural evidence links calcium binding and homophilic
      dimerization to DdCAD-1-mediated calcium-dependent cell-cell adhesion.
    supported_by:
    - reference_id: PMID:17057715
      supporting_text: Our results provide new insights into Ca(2+)-dependent
        mechanisms for cell-cell adhesion
core_functions:
- description: DdCAD-1 mediates calcium-dependent homophilic cell-cell adhesion
    at the onset of Dictyostelium development. Its N-terminal betagamma-crystallin
    domain drives self-association into a Ca2+-bound dimer that bridges adjacent
    cells, establishing the earliest EDTA/EGTA-sensitive (contact-site-B)
    adhesions on the outer surface of the plasma membrane.
  molecular_function:
    id: GO:0042802
    label: identical protein binding
  directly_involved_in:
  - id: GO:0016339
    label: calcium-dependent cell-cell adhesion
  locations:
  - id: GO:0009897
    label: external side of plasma membrane
  - id: GO:0071944
    label: cell periphery
  supported_by:
  - reference_id: PMID:8227052
    supporting_text: these in vitro assays provide direct evidence that gp24 is a
      cell adhesion molecule that most likely functions through a homophilic mode
      of interaction
  - reference_id: PMID:17057715
    supporting_text: we propose a model for the Ca(2+)-bound DdCAD-1 dimer as a
      basis for understanding DdCAD-1-mediated cell-cell adhesion
- description: DdCAD-1 is a calcium-binding protein; calcium binding stabilizes
    its structure, is required for homophilic adhesion, and is required for its
    import into contractile vacuoles during unconventional secretion.
  molecular_function:
    id: GO:0005509
    label: calcium ion binding
  locations:
  - id: GO:0009897
    label: external side of plasma membrane
  supported_by:
  - reference_id: PMID:8227052
    supporting_text: Binding studies showed that 45Ca2+ could bind to gp24
      blotted onto nitrocellulose membrane
  - reference_id: PMID:19875452
    supporting_text: Import of DdCAD-1 was compromised when two of its three
      Ca(2+)-binding sites were mutated, indicating a role for Ca(2+) in the
      import process
- description: Independently of its developmental adhesion role, secreted DdCAD-1
    acts as a calcium-dependent, galactose-specific lectin that binds and
    agglutinates Gram-negative bacteria (e.g. Klebsiella pneumoniae), forming a
    protective extracellular interface that limits exposure of feeding amoebae to
    bacterial toxicity.
  molecular_function:
    id: GO:0030246
    label: carbohydrate binding
  directly_involved_in:
  - id: GO:0050829
    label: defense response to Gram-negative bacterium
  locations:
  - id: GO:0005576
    label: extracellular region
  supported_by:
  - reference_id: PMID:31355329
    supporting_text: This suggests that CadA is a lectin that binds to
      carbohydrates on the surface of K. pneumoniae, perhaps to their
      lipopolysaccharide, which is rich in galactose moieties
  - reference_id: PMID:31355329
    supporting_text: CadA, a cell adhesion protein that functions in D. discoideum
      development, is also a bacterial agglutinin that forms a protective
      interface at the plaque edge that limits exposure of vegetative amoebae to
      bacteria
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/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: PMID:12135922
  title: Disruption of the gene encoding the cell adhesion molecule DdCAD-1 leads
    to aberrant cell sorting and cell-type proportioning during Dictyostelium development.
  findings:
  - statement: Loss of cadA reduces EDTA-sensitive (calcium-dependent) cell adhesion
      by half and perturbs cell-type proportioning and pattern formation.
    supporting_text: The cadA-null cells showed a 50% reduction in EDTA-sensitive
      cell adhesion
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: cadA-null loss-of-function study establishing DdCAD-1's role in
      calcium-dependent adhesion and developmental cell sorting; abstract-only in
      cache.
- id: PMID:15366765
  title: 'Comparison of molecular mechanisms mediating cell contact phenomena in model
    developmental systems: an exploration of universality.'
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Comparative review of cell-contact mechanisms; cited for cell
      cortex and aggregation TAS annotations but does not provide DdCAD-1-specific
      experimental detail in the abstract.
- id: PMID:16622066
  title: An activated Ras protein alters cell adhesion by dephosphorylating Dictyostelium
    DdCAD-1.
  findings:
  - statement: Activated RasG increases DdCAD-1-dependent cohesion and DdCAD-1 cell
      surface localization while reducing its phosphorylation.
    supporting_text: This increased cohesion was DdCAD-1-dependent and was correlated
      with increased localization of DdCAD-1 at the cell surface
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Genetic interaction linking RasG signaling to DdCAD-1 expression,
      dephosphorylation, and adhesion.
- id: PMID:16926386
  title: Proteomics fingerprinting of phagosome maturation and evidence for the role
    of a Galpha during uptake.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Large-scale phagosome proteomics (179 proteins); basis for a
      likely-incidental phagocytic vesicle localization.
- id: PMID:17057715
  title: Solution structures of the adhesion molecule DdCAD-1 reveal new insights
    into Ca(2+)-dependent cell-cell adhesion.
  findings:
  - statement: DdCAD-1 has two beta-sandwich domains; the N-terminal domain mediates
      homophilic binding and the C-terminal domain tethers it to the membrane.
    supporting_text: Whereas the N-terminal domain has a major role in homophilic
      binding, the C-terminal domain tethers the protein to the cell membrane
  - statement: A Ca2+-bound DdCAD-1 dimer provides the structural basis for
      DdCAD-1-mediated cell-cell adhesion.
    supporting_text: we propose a model for the Ca(2+)-bound DdCAD-1 dimer as a basis
      for understanding DdCAD-1-mediated cell-cell adhesion
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: NMR structures of Ca2+-free and Ca2+-bound DdCAD-1; defines the
      structural mechanism of calcium-dependent homophilic adhesion.
- id: PMID:19482547
  title: Proteomic analysis of Legionella-containing phagosomes isolated from Dictyostelium.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Legionella-containing phagosome proteomics (157 host proteins);
      basis for a likely-incidental phagocytic vesicle localization.
- id: PMID:19875452
  title: Cell adhesion molecule DdCAD-1 is imported into contractile vacuoles by membrane
    invagination in a Ca2+- and conformation-dependent manner.
  findings:
  - statement: DdCAD-1 is made as a soluble cytoplasmic protein and imported into
      contractile vacuoles for transport to the plasma membrane.
    supporting_text: DdCAD-1 is synthesized in the cytoplasm as a soluble protein
      and then transported by contractile vacuoles to the plasma membrane for surface
      presentation or secretion
  - statement: Calcium binding is required for import of DdCAD-1 into contractile
      vacuoles.
    supporting_text: Import of DdCAD-1 was compromised when two of its three Ca(2+)-binding
      sites were mutated, indicating a role for Ca(2+) in the import process
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Mechanistic study of the unconventional (contractile-vacuole)
      secretion route; full text available.
- id: PMID:21561987
  title: The cell adhesion molecule DdCAD-1 regulates morphogenesis through differential
    spatiotemporal expression in Dictyostelium discoideum.
  findings:
  - statement: Differential distribution of DdCAD-1 on prestalk versus prespore
      cells governs cell sorting in slugs.
    supporting_text: These results show that DdCAD-1 influences the sorting behavior
      of cells in slugs by its differential distribution on the prestalk and prespore
      cells
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Links DdCAD-1 spatiotemporal expression to cell sorting and
      morphogenesis; abstract-only in cache.
- id: PMID:23441816
  title: Ca(2+) -calmodulin interacts with DdCAD-1 and promotes DdCAD-1 transport
    by contractile vacuoles in Dictyostelium cells.
  findings:
  - statement: Only Ca2+-bound calmodulin binds DdCAD-1, and calmodulin promotes
      DdCAD-1 import into contractile vacuoles.
    supporting_text: Co-immunoprecipitation and pull-down studies showed that only
      Ca(2+) -bound calmodulin was able to bind DdCAD-1
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Establishes the direct DdCAD-1 / Ca2+-calmodulin interaction and
      its role in trafficking; abstract-only in cache.
- id: PMID:24036346
  title: Dictyostelium lipid droplets host novel proteins.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Lipid droplet proteomics; DdCAD-1 not a functional lipid droplet
      protein, likely a co-purification hit.
- id: PMID:24426151
  title: ATP-Binding Cassette Transporter B4 Anchors the Cell Adhesion Molecule DdCAD-1
    to Cell Membrane in Dictyostelium discoideum.
  findings:
  - statement: The plasma membrane anchor that tethers soluble DdCAD-1 to the cell
      surface is the ABC transporter ABCB4.
    supporting_text: to identify ABCB4 as the anchor protein of DdCAD-1
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Identifies ABCB4 as the DdCAD-1 membrane anchor by cross-linking
      and mass spectrometry; full text available.
- id: PMID:26152465
  title: Proteomic profiling of the extracellular matrix (slime sheath) of Dictyostelium
    discoideum.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Slug ECM (slime sheath) proteomics; consistent with DdCAD-1 being
      secreted, though ECM is a secondary localization.
- id: PMID:26449461
  title: 'Curcumin inhibits development and cell adhesion in Dictyostelium discoideum:
    Implications for YakA signaling and GST enzyme function.'
  findings:
  - statement: Curcumin suppresses expression of the cell adhesion proteins DdCAD
      and csA, delaying adhesion and development.
    supporting_text: expression of the extracellular matrix/cell adhesion proteins
      (DdCAD and csA)
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Shows DdCAD expression is down-regulated by curcumin; an indirect
      drug effect rather than a DdCAD-1 molecular function.
- id: PMID:31355329
  title: Social amoebae establish a protective interface with their bacterial associates
    by lectin agglutination.
  findings:
  - statement: Secreted CadA is a calcium-dependent, galactose-specific lectin that
      agglutinates Gram-negative bacteria and protects amoebae from bacterial
      toxicity.
    supporting_text: CadA, a cell adhesion protein that functions in D. discoideum
      development, is also a bacterial agglutinin that forms a protective interface
      at the plaque edge that limits exposure of vegetative amoebae to bacteria
  - statement: CadA binding to K. pneumoniae is inhibited by galactose, consistent
      with a lectin recognizing bacterial surface carbohydrate.
    supporting_text: This suggests that CadA is a lectin that binds to carbohydrates
      on the surface of K. pneumoniae, perhaps to their lipopolysaccharide, which
      is rich in galactose moieties
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Establishes the moonlighting lectin/agglutinin function of CadA in
      antibacterial defense; full text available.
- id: PMID:38986731
  title: Trafficking of adhesion and aggregation-modulating proteins during the early
    stages of Dictyostelium development.
  findings:
  - statement: CadA localizes to the cell periphery in growth-phase and starved
      cells, and its intracellular/extracellular levels are modulated by autophagy
      and trafficking genes.
    supporting_text: As for CadA, it localizes to the cell periphery in growth-phase
      and starved cells
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Trafficking study; source of the cell periphery IDA localization.
- id: PMID:7593293
  title: Identification of major proteins associated with Dictyostelium discoideum
    endocytic vesicles.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Endocytic vesicle proteomics; DdCAD-1 detection likely incidental.
- id: PMID:8227052
  title: Characterization of the cell adhesion molecule gp24 in Dictyostelium discoideum.
    Mediation of cell-cell adhesion via a Ca(2+)-dependent mechanism.
  findings:
  - statement: gp24 (DdCAD-1) is a cell adhesion molecule that functions through a
      homophilic, calcium-dependent mechanism and binds calcium.
    supporting_text: these in vitro assays provide direct evidence that gp24 is a
      cell adhesion molecule that most likely functions through a homophilic mode
      of interaction
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Foundational biochemical characterization of gp24/DdCAD-1 adhesion
      and calcium binding; abstract-only in cache.
- id: PMID:8663243
  title: Molecular cloning and characterization of DdCAD-1, a Ca2+-dependent cell-cell
    adhesion molecule, in Dictyostelium discoideum.
  findings:
  - statement: DdCAD-1 associates with the ecto-surface of the plasma membrane
      despite lacking a signal peptide or transmembrane domain.
    supporting_text: immunofluorescence microscopy demonstrates the association of
      DdCAD-1 with the ecto-surface of the plasma membrane
  - statement: Cell binding activity resides in the N-terminal segment, not the
      C-terminal Ca2+-binding domain.
    supporting_text: the cell binding activity is dependent on the amino-terminal
      segment and not the carboxyl-terminal Ca2+-binding domain
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Cloning and characterization of DdCAD-1; establishes surface
      localization and domain organization; abstract-only in cache.
- id: PMID:8806827
  title: Novel redistribution of the Ca(2+)-dependent cell adhesion molecule DdCAD-1
    during development of Dictyostelium discoideum.
  findings:
  - statement: Before aggregation DdCAD-1 relocates from diffuse cytoplasm to the
      cell periphery and becomes enriched on membrane ruffles, lamellipodia, and
      filopodia at cell contacts.
    supporting_text: A high concentration of DdCAD-1 also becomes associated with
      lamellipodia and filopodia, which often appear to participate in cell contact
      formation
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Documents developmental redistribution of DdCAD-1 to surface
      protrusions; source of ruffle/lamellipodium/filopodium localizations.
- id: PMID:9265658
  title: The cell adhesion molecule DdCAD-1 in Dictyostelium is targeted to the cell
    surface by a nonclassical transport pathway involving contractile vacuoles.
  findings:
  - statement: DdCAD-1 is transported to the cell surface from the cytosol via
      contractile vacuoles, a nonclassical secretion pathway.
    supporting_text: DdCAD-1 is transported to the cell surface via contractile
      vacuoles, which are normally involved in osmoregulation
  - statement: DdCAD-1 preferentially associates with contractile vacuoles and is
      present both on the surface and in the cytosol.
    supporting_text: Immunofluorescence microscopy and subcellular fractionation
      revealed a preferential association of DdCAD-1 with contractile vacuoles
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: First demonstration of contractile-vacuole-mediated unconventional
      secretion of DdCAD-1; full text available.

Gene Description

Existing Annotations Review

Core Functions

DdCAD-1 is a calcium-binding protein; calcium binding stabilizes its structure, is required for homophilic adhesion, and is required for its import into contractile vacuoles during unconventional secretion.

References

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