dhkA

id: Q54U87
gene_symbol: dhkA
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:44689
  label: Dictyostelium discoideum
description: DhkA is a large multi-domain hybrid histidine kinase that acts as the
  cell-surface receptor for the peptide signal SDF-2 (spore differentiation factor
  2) during terminal differentiation of Dictyostelium discoideum. The N-terminal
  half of the protein forms two transmembrane helices flanking an extracellular
  CHASE-type ligand-binding loop, while the C-terminal half contains the cytoplasmic
  catalytic machinery, comprising a histidine kinase (HisKA/HATPase) core with the
  autophosphorylated His1395 and a C-terminal response-regulator receiver domain
  carrying the relay Asp2075. DhkA autophosphorylates on histidine in an
  ATP-dependent manner and relays the phosphoryl group to its own aspartate and onward
  through the phosphotransfer protein RdeA to the response regulator of the cAMP
  phosphodiesterase RegA. Binding of the SDF-2 ligand (a proteolytic peptide derived
  from the acyl-CoA-binding protein AcbA) inhibits DhkA kinase/phosphorelay activity,
  lowering RegA phosphodiesterase activity so that intracellular cAMP rises and PKA
  is activated, triggering rapid encapsulation of prespore cells into spores. Through
  this two-component phosphorelay DhkA controls prestalk gene expression, spore
  encapsulation, and the timing of culmination in the multicellular fruiting body.
existing_annotations:
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: Phylogenetic inference that DhkA acts at the plasma membrane is
      consistent with direct experimental evidence that DhkA is a membrane-spanning
      receptor histidine kinase.
    action: ACCEPT
    reason: DhkA is a multi-pass membrane protein with an extracellular ligand-binding
      loop and a cytoplasmic catalytic domain, directly demonstrated by epitope-tagging
      topology experiments. Plasma membrane localization is well supported.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: The results presented here show that DhkA is a membrane-spanning
        histidine kinase and is likely to be a receptor which mediates the cellular
        response to SDF-2 in the genetic pathway that eventually leads to PKA-dependent
        differentiation.
- term:
    id: GO:0000155
    label: phosphorelay sensor kinase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: Phylogenetic inference of phosphorelay sensor kinase activity is
      strongly corroborated by direct biochemical and genetic evidence for DhkA
      histidine autophosphorylation and phosphorelay.
    action: ACCEPT
    reason: DhkA autophosphorylates on His1395 and relays phosphate to Asp2075 and
      onward to RdeA/RegA, the defining activity of a phosphorelay sensor kinase.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: DhkA is a protein kinase able to autophosphorylate on a
        histidine residue
- term:
    id: GO:0000160
    label: phosphorelay signal transduction system
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: DhkA operates within a two-component phosphorelay signal transduction
      system, transferring phosphate from its histidine through RdeA to the RegA
      response regulator.
    action: ACCEPT
    reason: Directly supported by both biochemical and genetic evidence for a
      His-to-Asp phosphorelay linking DhkA to RdeA and RegA.
    supported_by:
    - reference_id: PMID:15897458
      supporting_text: The SDF-2 receptor in Dictyostelium is a membrane-associated
        histidine kinase, DhkA, that relays phosphate via a histidine in RdeA to
        response regulator regions on several proteins
- term:
    id: GO:0000155
    label: phosphorelay sensor kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: Electronic inference of phosphorelay sensor kinase activity from
      InterPro histidine-kinase domains agrees with experimentally demonstrated
      activity.
    action: ACCEPT
    reason: Redundant with the experimentally supported IMP/IBA annotations to the
      same term; the domain-based inference is correct.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: DhkA is a protein kinase able to autophosphorylate on a
        histidine residue
- term:
    id: GO:0000160
    label: phosphorelay signal transduction system
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: InterPro2GO inference from the response-regulator receiver domain that
      DhkA participates in a phosphorelay signal transduction system.
    action: ACCEPT
    reason: Correct and redundant with the experimentally supported IBA annotation
      to the same term.
    supported_by:
    - reference_id: PMID:15897458
      supporting_text: The SDF-2 receptor in Dictyostelium is a membrane-associated
        histidine kinase, DhkA, that relays phosphate via a histidine in RdeA to
        response regulator regions on several proteins
- term:
    id: GO:0004673
    label: protein histidine kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000003
  qualifier: enables
  review:
    summary: EC-based inference (EC 2.7.13.3) of protein histidine kinase activity.
      DhkA autophosphorylates on a histidine, consistent with this activity, though
      the more specific phosphorelay sensor kinase term better captures its
      two-component function.
    action: KEEP_AS_NON_CORE
    reason: The activity is correct (His autophosphorylation) but this general
      protein histidine kinase term is largely subsumed by the more informative
      phosphorelay sensor kinase activity (GO:0000155) and transmembrane receptor
      histidine kinase activity (GO:0009784) annotations that represent the core
      function.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: Site-directed mutagenesis of histidine 1395 to glutamine in
        the catalytic domain blocked autophosphorylation.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: Electronic inference of plasma membrane localization from the UniProt
      subcellular location, consistent with the direct experimental evidence.
    action: ACCEPT
    reason: Redundant with the experimentally supported IDA annotation to plasma
      membrane; DhkA is a multi-pass plasma membrane protein.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: The results presented here show that DhkA is a membrane-spanning
        histidine kinase and is likely to be a receptor which mediates the cellular
        response to SDF-2 in the genetic pathway that eventually leads to PKA-dependent
        differentiation.
- term:
    id: GO:0007165
    label: signal transduction
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: General signal transduction inference from InterPro. Correct but far
      less informative than the specific phosphorelay signal transduction system
      annotation.
    action: KEEP_AS_NON_CORE
    reason: This is a high-level parent of the more specific and experimentally
      supported phosphorelay signal transduction system (GO:0000160) annotation and
      adds little information on its own.
    supported_by:
    - reference_id: PMID:15897458
      supporting_text: The SDF-2 receptor in Dictyostelium is a membrane-associated
        histidine kinase, DhkA, that relays phosphate via a histidine in RdeA to
        response regulator regions on several proteins
- term:
    id: GO:0016772
    label: transferase activity, transferring phosphorus-containing groups
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: Very general molecular function parent inferred from InterPro. Correct
      (kinase transfers phosphate) but uninformative relative to the specific
      histidine kinase annotations.
    action: KEEP_AS_NON_CORE
    reason: This broad grouping term is a distant parent of the specific and
      experimentally supported kinase activities already annotated; it does not
      represent the core function on its own.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: DhkA is a protein kinase able to autophosphorylate on a
        histidine residue
- term:
    id: GO:0009784
    label: transmembrane receptor histidine kinase activity
  evidence_type: IMP
  original_reference_id: PMID:10373524
  qualifier: enables
  review:
    summary: Core molecular function. DhkA is a membrane-spanning receptor histidine
      kinase whose extracellular loop binds the SDF-2 signal and whose cytoplasmic
      catalytic domain autophosphorylates on His1395; mutation of His1395 abolishes
      activity and function.
    action: ACCEPT
    reason: Directly supported by topology mapping (extracellular ligand loop,
      cytoplasmic catalytic domain), in vitro autophosphorylation, and mutagenesis
      of the essential catalytic histidine.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: The results presented here show that DhkA is a membrane-spanning
        histidine kinase and is likely to be a receptor which mediates the cellular
        response to SDF-2 in the genetic pathway that eventually leads to PKA-dependent
        differentiation.
    - reference_id: PMID:10373524
      supporting_text: Thus, the 310-amino-acid loop between the transmembrane
        domains of DhkA is exposed to the intercellular medium and appears to be
        critical for ligand binding and activation of DhkA.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:10373524
  qualifier: is_active_in
  review:
    summary: Direct experimental evidence places DhkA in the plasma membrane, with
      an extracellular ligand-binding loop and a cytoplasmic catalytic domain
      established by epitope-tag protease-protection topology mapping.
    action: ACCEPT
    reason: Core cellular location, directly demonstrated. DhkA is a bona fide
      membrane-spanning receptor.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: By inserting MYC 6 epitopes into DhkA, we were able to show
        that the loop is extracellular while the catalytic domain is cytoplasmic.
- term:
    id: GO:0009897
    label: external side of plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:10373524
  qualifier: is_active_in
  review:
    summary: The 310-amino-acid ligand-binding loop of DhkA between its two
      transmembrane domains is exposed on the external side of the plasma membrane,
      demonstrated by protease-protection experiments.
    action: ACCEPT
    reason: Directly supported topology; the SDF-2-binding loop faces the
      extracellular (intercellular) medium.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: Thus, the 310-amino-acid loop between the transmembrane
        domains of DhkA is exposed to the intercellular medium and appears to be
        critical for ligand binding and activation of DhkA.
- term:
    id: GO:0009898
    label: cytoplasmic side of plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:10373524
  qualifier: is_active_in
  review:
    summary: The catalytic histidine kinase and receiver domains of DhkA face the
      cytoplasmic side of the plasma membrane, where the relay aspartate can act on
      its downstream response regulator.
    action: ACCEPT
    reason: Directly supported topology; the C-terminal catalytic portion is
      internal/cytoplasmic.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: The carboxy-terminal portion of DhkA that carries the
        conserved aspartate to which the phosphate is relayed appears to be internal,
        where it can affect its response regulator.
- term:
    id: GO:0140582
    label: adenylate cyclase-activating G protein-coupled cAMP receptor signaling
      pathway
  evidence_type: IMP
  original_reference_id: PMID:12796307
  qualifier: involved_in
  review:
    summary: This annotation captures the finding that disruption of dhkA strongly
      lowers intracellular cAMP levels, connecting DhkA to cAMP metabolism. However,
      the specific term describes the cell-surface cAMP GPCR (cAR)-driven pathway
      that activates adenylate cyclase during aggregation, which is a poor fit for
      DhkA. DhkA is a histidine kinase that acts on intracellular cAMP through the
      RdeA/RegA phosphodiesterase and PKA during culmination, not a G protein-coupled
      cAMP receptor pathway.
    action: MARK_AS_OVER_ANNOTATED
    reason: The underlying genetic evidence (dhkA mutants have severalfold reduced
      cAMP) is real, but the chosen term denotes the GPCR/adenylate-cyclase
      aggregation pathway rather than the intracellular RegA/PKA phosphorelay pathway
      in which DhkA actually acts. The term over-specifies an inappropriate pathway;
      the DhkA cAMP connection is better represented by its phosphorelay and
      sporulation annotations.
    supported_by:
    - reference_id: PMID:12796307
      supporting_text: The levels of cAMP are relatively constant during
        multicellular development in all strains except the dhkA mutant, in which it
        is reduced at least sixfold.
- term:
    id: GO:0009784
    label: transmembrane receptor histidine kinase activity
  evidence_type: IDA
  original_reference_id: PMID:15897458
  qualifier: enables
  review:
    summary: Core molecular function, independently supported. Using a yeast
      reconstitution system, DhkA functions as a constitutive histidine kinase whose
      phosphorelay activity is inhibited upon binding its SDF-2 ligand.
    action: ACCEPT
    reason: Direct functional demonstration that DhkA is a ligand-regulated receptor
      histidine kinase; SDF-2 binding inhibits its phosphorelay activity.
    supported_by:
    - reference_id: PMID:15897458
      supporting_text: Using a yeast system we show that ligand binding to the SDF-2
        receptor histidine kinase, DhkA, inhibits phosphorelay, which can account for
        its ability to induce rapid sporulation.
    - reference_id: PMID:15897458
      supporting_text: It appears that DhkA functions as a constitutive kinase in
        yeast that is inhibited upon ligand binding.
- term:
    id: GO:0000155
    label: phosphorelay sensor kinase activity
  evidence_type: IMP
  original_reference_id: PMID:10373524
  qualifier: enables
  review:
    summary: Core molecular function. Genetic and biochemical evidence show DhkA
      autophosphorylates on His1395 and relays phosphate to the receiver aspartate
      Asp2075; both residues are required for function.
    action: ACCEPT
    reason: Mutation of His1395 blocks autophosphorylation and mutation of Asp2075
      compromises function, directly establishing DhkA as a phosphorelay sensor
      kinase.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: Site-directed mutagenesis of histidine 1395 to glutamine in
        the catalytic domain blocked autophosphorylation.
    - reference_id: PMID:10373524
      supporting_text: DhkA is a protein kinase able to autophosphorylate on a
        histidine residue
- term:
    id: GO:0031288
    label: sorocarp morphogenesis
  evidence_type: IGI
  original_reference_id: PMID:10373524
  qualifier: acts_upstream_of_or_within
  review:
    summary: DhkA acts within the signaling pathway that shapes the fruiting body
      (sorocarp) during culmination; genetic interaction with a downstream kinase
      (DhkB) supports its role in morphogenesis, though this is a developmental
      consequence rather than the core molecular activity.
    action: KEEP_AS_NON_CORE
    reason: The role in sorocarp morphogenesis is a valid developmental output of
      DhkA phosphorelay signaling but is downstream of and secondary to its core
      receptor histidine kinase function.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: The results presented here show that DhkA is a membrane-spanning
        histidine kinase and is likely to be a receptor which mediates the cellular
        response to SDF-2 in the genetic pathway that eventually leads to PKA-dependent
        differentiation.
- term:
    id: GO:0030587
    label: sorocarp development
  evidence_type: HMP
  original_reference_id: PMID:17659086
  qualifier: acts_upstream_of_or_within
  review:
    summary: High-throughput mutant phenotyping shows dhkA insertion mutants have
      defects specific to the slug-to-culmination stage, including the characteristic
      long-stalk phenotype, consistent with a role in sorocarp development.
    action: KEEP_AS_NON_CORE
    reason: Well-supported developmental role, but this whole-organism developmental
      process is a downstream consequence of DhkA's core signaling function rather
      than the molecular activity itself.
    supported_by:
    - reference_id: PMID:17659086
      supporting_text: In contrast, dhkA and acrA show mutant phenotypes only at
        later stages consistent with their specific roles during slug to culmination
        stage.
    - reference_id: PMID:17659086
      supporting_text: long stalks in dhkA [28] also agree well with known mutant
        phenotypes
- term:
    id: GO:0030435
    label: sporulation resulting in formation of a cellular spore
  evidence_type: IMP
  original_reference_id: PMID:12796307
  qualifier: acts_upstream_of_or_within
  review:
    summary: DhkA controls spore encapsulation. Disruption of dhkA suppresses the
      excessive sporulation of fbxA mutants and dhkA mutants are impaired in
      sporulation, linking DhkA to the control of spore formation via the RegA/cAMP/PKA
      pathway.
    action: ACCEPT
    reason: DhkA is a central controller of the timing of prespore-cell encapsulation
      into spores; multiple independent studies place it upstream of sporulation.
    supported_by:
    - reference_id: PMID:12796307
      supporting_text: Studies of dhk A indicate that it is important at late stages
        of development, when the prespore cells encapsulate.
- term:
    id: GO:0030587
    label: sorocarp development
  evidence_type: IMP
  original_reference_id: PMID:12796307
  qualifier: acts_upstream_of_or_within
  review:
    summary: dhkA mutation modifies fruiting-body development and rescues the
      culmination deficiency of fbxA mutants, consistent with a role in sorocarp
      development.
    action: KEEP_AS_NON_CORE
    reason: Valid developmental role downstream of the core phosphorelay signaling
      function; secondary to the molecular activity.
    supported_by:
    - reference_id: PMID:12796307
      supporting_text: Studies of dhk A indicate that it is important at late stages
        of development, when the prespore cells encapsulate.
- term:
    id: GO:0030435
    label: sporulation resulting in formation of a cellular spore
  evidence_type: IMP
  original_reference_id: PMID:8670894
  qualifier: acts_upstream_of_or_within
  review:
    summary: The original dhkA mutant characterization showed DhkA functions in the
      control of terminal differentiation of prespore cells, i.e. sporulation.
    action: ACCEPT
    reason: Foundational genetic evidence that DhkA controls the terminal
      differentiation (encapsulation) of prespore cells into spores.
    supported_by:
    - reference_id: PMID:8670894
      supporting_text: In Dictyostelium, we found that DhkA functions both in the
        regulation of prestalk gene expression and in the control of the terminal
        differentiation of prespore cells.
- term:
    id: GO:0031150
    label: sorocarp stalk development
  evidence_type: IMP
  original_reference_id: PMID:8670894
  qualifier: acts_upstream_of_or_within
  review:
    summary: DhkA functions in the regulation of prestalk gene expression, and dhkA
      mutants show stalk defects (including long stalks), supporting a role in stalk
      (sorocarp stalk) development.
    action: KEEP_AS_NON_CORE
    reason: Regulation of prestalk gene expression and stalk morphology is a
      developmental output of DhkA signaling, secondary to its core molecular
      function.
    supported_by:
    - reference_id: PMID:8670894
      supporting_text: In Dictyostelium, we found that DhkA functions both in the
        regulation of prestalk gene expression and in the control of the terminal
        differentiation of prespore cells.
- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: TAS
  original_reference_id: PMID:9191038
  qualifier: enables
  review:
    summary: DhkA binds ATP as the phosphoryl donor for histidine autophosphorylation,
      the defining activity of autophosphorylating histidine kinases.
    action: ACCEPT
    reason: ATP binding is required for and directly evidenced by the ATP-dependent
      histidine autophosphorylation of the DhkA catalytic domain.
    supported_by:
    - reference_id: PMID:10373524
      supporting_text: incorporation of labelled phosphate from ATP consistent with
        histidine autophosphorylation
    - reference_id: PMID:9191038
      supporting_text: A transmembrane histidine kinase encoded by dhkA accumulates
        when Dictyostelium cells aggregate during development.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000003
  title: Gene Ontology annotation based on Enzyme Commission mapping
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:10373524
  title: SDF-2 induction of terminal differentiation in Dictyostelium discoideum is
    mediated by the membrane-spanning sensor kinase DhkA.
  findings:
  - statement: DhkA is a membrane-spanning receptor histidine kinase with an
      extracellular ligand-binding loop and a cytoplasmic catalytic domain that
      mediates the SDF-2 response.
    supporting_text: By inserting MYC 6 epitopes into DhkA, we were able to show that
      the loop is extracellular while the catalytic domain is cytoplasmic.
  - statement: DhkA autophosphorylates on His1395 in an ATP-dependent manner; this
      histidine is essential for activity.
    supporting_text: Site-directed mutagenesis of histidine 1395 to glutamine in the
      catalytic domain blocked autophosphorylation.
  - statement: The cAMP phosphodiesterase RegA and PKA act downstream of DhkA.
    supporting_text: Suppressor studies indicate that the cyclic AMP (cAMP)
      phosphodiesterase RegA and the cAMP-dependent protein kinase PKA act downstream
      of DhkA.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Primary paper establishing DhkA topology, His1395 autophosphorylation,
      Asp2075 relay, and its role as the SDF-2 receptor upstream of RegA/PKA. Quotes
      verified against cached full text.
- id: PMID:12796307
  title: Genetic interactions of the E3 ubiquitin ligase component FbxA with cyclic
    AMP metabolism and a histidine kinase signaling pathway during Dictyostelium discoideum
    development.
  findings:
  - statement: DhkA is a receptor histidine kinase with a CHASE (cytokinin-receptor-like)
      domain and a histidine kinase domain.
    supporting_text: The DhkA molecule has several domains including a CHASE domain,
      which was identified as a receptor for plant cytokinins, and a histidine kinase
      domain
  - statement: dhkA disruption strongly reduces intracellular cAMP levels and
      suppresses the fbxA sporulation defect.
    supporting_text: The levels of cAMP are relatively constant during multicellular
      development in all strains except the dhkA mutant, in which it is reduced at
      least sixfold.
  reference_review:
    relevance: HIGH
    correctness: DISPUTED
    review_notes: >-
      Solid genetic evidence linking dhkA to RegA/cAMP and sporulation. The
      authors' proposed directionality (that DhkA activates RegA
      phosphodiesterase) explicitly contradicts Wang et al.
      (PMID:10373524 / PMID:15897458), who show ligand binding to DhkA inhibits
      phosphorelay to RegA; the direction of DhkA-RegA regulation is therefore
      contested. Hand-curated expert assessment - the Wang/Anjard-Loomis
      inhibition model is the better-supported working model. DhkA
      autophosphorylation on His1395 and phosphorelay through RdeA to the RegA
      receiver aspartate are biochemically demonstrated, and SDF-2 binding lowers
      this relay so RegA is dephosphorylated and inactivated, raising
      intracellular cAMP and activating PKA to trigger encapsulation. The fbxA
      genetic-interaction study reported here infers the opposite direction only
      indirectly, so it is recorded as a contested minority interpretation
      pending direct measurement of the RegA phosphorylation state in dhkA-null
      versus SDF-2-treated cells.
- id: PMID:15897458
  title: Peptide signaling during terminal differentiation of Dictyostelium.
  findings:
  - statement: SDF-2 is a peptide processed from the acyl-CoA-binding protein AcbA and
      is the ligand of the DhkA receptor histidine kinase.
    supporting_text: Using a yeast system we show that ligand binding to the SDF-2
      receptor histidine kinase, DhkA, inhibits phosphorelay, which can account for
      its ability to induce rapid sporulation.
  - statement: DhkA relays phosphate via RdeA to the RegA response regulator; reduced
      phosphorelay lowers RegA activity, raising cAMP and activating PKA.
    supporting_text: Reduced phosphorelay to the internal phosphodiesterase RegA via
      the small H2 protein RdeA results in a decrease in phosphodiesterase activity,
      leading to accumulation of cAMP and resulting activation of PKA
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Establishes SDF-2 as an AcbA-derived peptide ligand and, via a yeast
      reconstitution assay, that ligand binding inhibits DhkA phosphorelay. Quotes
      verified against cached full text.
- id: PMID:17659086
  title: High-throughput analysis of spatio-temporal dynamics in Dictyostelium.
  findings:
  - statement: dhkA insertion mutants show developmental phenotypes specific to the
      slug-to-culmination stage, consistent with a late-development role.
    supporting_text: In contrast, dhkA and acrA show mutant phenotypes only at later
      stages consistent with their specific roles during slug to culmination stage.
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Large-scale phenotyping screen; recovers the known late-development
      (long-stalk) dhkA phenotype, supporting the sorocarp development annotation.
- id: PMID:8670894
  title: A two-component histidine kinase gene that functions in Dictyostelium development.
  findings:
  - statement: DhkA encodes a two-component histidine kinase with histidine kinase and
      response regulator domains and functions in prestalk gene regulation and prespore
      terminal differentiation.
    supporting_text: In Dictyostelium, we found that DhkA functions both in the
      regulation of prestalk gene expression and in the control of the terminal
      differentiation of prespore cells.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Original identification and functional characterization of dhkA
      (abstract only in cache; full text read by the dictyBase curator for the IMP
      annotations).
- id: PMID:9191038
  title: Histidine kinases in signal transduction pathways of eukaryotes.
  findings:
  - statement: DhkA is a transmembrane histidine kinase whose activation inhibits the
      RegA cAMP phosphodiesterase, thereby regulating PKA and spore encapsulation.
    supporting_text: Activation of DhkA results in the inhibition of its response
      regulator, RegA, which is a cAMP phosphodiesterase that regulates the cAMP
      dependent protein kinase PKA.
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Review (TAS) summarizing eukaryotic histidine kinase two-component
      signaling and the DhkA-RegA-PKA circuit; supports ATP-dependent histidine
      kinase activity. Abstract only in cache.
suggested_experiments:
- hypothesis: >-
    SDF-2 binding to DhkA inhibits, rather than activates, the His-Asp
    phosphorelay to RegA, thereby lowering RegA phosphodiesterase activity.
  description: >-
    Measure the phosphorylation state of the RegA receiver aspartate (for
    example by Phos-tag electrophoresis or a phospho-specific readout) in
    wild-type cells with and without added SDF-2 and in dhkA-null cells at the
    onset of encapsulation. The inhibition model predicts SDF-2 lowers RegA
    phosphorylation, resolving the contested DhkA-RegA directionality.
  experiment_type: biochemical phosphorelay assay
core_functions:
- description: DhkA acts as the membrane-spanning receptor histidine kinase for the
    SDF-2 peptide signal. Its extracellular CHASE-type loop binds SDF-2 and its
    cytoplasmic catalytic domain autophosphorylates on His1395 using ATP, functioning
    as a ligand-regulated sensor kinase whose activity is inhibited upon SDF-2 binding.
  molecular_function:
    id: GO:0009784
    label: transmembrane receptor histidine kinase activity
  locations:
  - id: GO:0005886
    label: plasma membrane
  - id: GO:0009897
    label: external side of plasma membrane
  - id: GO:0009898
    label: cytoplasmic side of plasma membrane
  directly_involved_in:
  - id: GO:0000160
    label: phosphorelay signal transduction system
  supported_by:
  - reference_id: PMID:10373524
    supporting_text: The results presented here show that DhkA is a membrane-spanning
      histidine kinase and is likely to be a receptor which mediates the cellular
      response to SDF-2 in the genetic pathway that eventually leads to PKA-dependent
      differentiation.
  - reference_id: PMID:15897458
    supporting_text: Using a yeast system we show that ligand binding to the SDF-2
      receptor histidine kinase, DhkA, inhibits phosphorelay, which can account for
      its ability to induce rapid sporulation.
- description: DhkA operates as a phosphorelay sensor kinase, relaying phosphate from
    its autophosphorylated His1395 to the receiver aspartate Asp2075 and onward via
    RdeA to the RegA response regulator, thereby controlling intracellular cAMP and
    PKA activity that trigger spore encapsulation.
  molecular_function:
    id: GO:0000155
    label: phosphorelay sensor kinase activity
  directly_involved_in:
  - id: GO:0030435
    label: sporulation resulting in formation of a cellular spore
  supported_by:
  - reference_id: PMID:10373524
    supporting_text: DhkA is a protein kinase able to autophosphorylate on a histidine
      residue
  - reference_id: PMID:15897458
    supporting_text: The SDF-2 receptor in Dictyostelium is a membrane-associated
      histidine kinase, DhkA, that relays phosphate via a histidine in RdeA to
      response regulator regions on several proteins