PdsA/DdPDE1 (DICDI, UniProt P12019) — Adjudication of two negative-regulation GO claims

Focus: function_assignment · Hypothesis slug: extracellular-pde-and-camp-pathway-regulation
Terms adjudicated: GO:0110034 (negative regulation of adenylate cyclase-activating glucose-activated G protein-coupled receptor signaling pathway) and GO:0141162 (negative regulation of cAMP/PKA signal transduction).

Executive Judgment

Verdict: REFUTED / over-annotated for both terms as assigned to PdsA.

Both GO terms are already present on P12019 only as IBA (phylogenetic, ECO:0000318) annotations propagated from fungal cyclic-nucleotide phosphodiesterase orthologs via PANTHER family PTN002001416 (GO:0110034 ← S. pombe cgs2/Pde1, PomBase SPCC285.09c; GO:0141162 ← C. albicans PDE2, CGD CAL0000177603). Neither is backed by a Dictyostelium experiment.

• Claim A (GO:0110034): The GO term specifically denotes a glucose-activated GPCR→adenylate-cyclase pathway (the fungal Gpr1/Gpa2→Cyr1→cAMP→PKA glucose-sensing system). Dictyostelium has no such pathway; its adenylate-cyclase (ACA)-activating receptor cAR1 is cAMP-activated, not glucose-activated. PdsA's genuine negative-regulatory role — degrading the extracellular cAMP ligand of the cAR receptors — is real but is the wrong biological pathway for this term. The term is factually inapplicable, independent of PdsA being secreted.
• Claim B (GO:0141162): PdsA degrades the extracellular cAMP pool. PKA is activated by the intracellular cAMP pool, whose direct negative regulator is the cytosolic PDE RegA (Q23917). The direct catalytic step in cAMP/PKA signal transduction is RegA's, not PdsA's. PdsA can influence PKA only indirectly through cAR-receptor feedback/compartment coupling, which does not justify a direct BP annotation.

Most important caveat: This is a compartment/term-specificity judgement, not a claim that PdsA is irrelevant to cAMP signaling. PdsA is a bona-fide negative regulator of the extracellular cAMP relay/GPCR loop — that role is already captured by experimentally supported terms (GO:0007193 IMP, GO:1900115 IMP). The two seed terms should be removed as ortholog carry-over, not replaced with themselves.

Decisive primary evidence (added Iteration 2): Bader, Kortholt & Van Haastert 2007 (PMID:17040207) biochemically partition all seven Dictyostelium PDEs across three cyclic-nucleotide pools and state that extracellular cAMP is degraded predominantly by DdPDE1 (= PdsA) and its homolog DdPDE7, whereas intracellular cAMP (which "mediates development") is degraded by DdPDE2 (= RegA) and DdPDE6. This is a direct, quantitative pool assignment — not an inference from secretion — that separates PdsA (extracellular) from the RegA-controlled intracellular/PKA-relevant pool.

Correct-term note: GO does provide a non-glucose term, GO:0106072 "negative regulation of adenylate cyclase-activating G protein-coupled receptor signaling pathway", and a cAMP-receptor pathway term GO:0140582 "adenylate cyclase-activating G protein-coupled cAMP receptor signaling pathway". These, not the fungal glucose term GO:0110034, are the appropriate vocabulary if a receptor-pathway BP annotation is desired for PdsA's cAR/ACA context. (Note: GO:0043951 "negative regulation of cAMP-mediated signaling" is obsolete and unusable.)

Evidence Matrix

Provenance artifacts (computed this run): /tmp/go_decision_table.csv, /tmp/evidence_matrix.csv, /tmp/GO0110034_composition.png.

GO Curation Implications (leads — require curator verification)

Do not default to "protein binding": the informative MF (cAMP phosphodiesterase, GO:0004115) and the correct BP terms are already available.

Directionality nuance (curator-verify): the currently retained BP term GO:0007193 is adenylate cyclase-inhibiting GPCR signaling, but the characterized Dictyostelium biology is that cAR1 activates adenylate cyclase (ACA) and PdsA negatively regulates that loop by degrading the extracellular cAMP ligand. On directional grounds GO:0106072 (negative regulation of adenylate cyclase-activating GPCR signaling) is a more accurate BP than GO:0007193. A curator may wish to consider replacing GO:0007193 with GO:0106072 (context GO:0140582, cAMP-receptor pathway), rather than simply retaining GO:0007193.

Mechanistic Scope

• Direct molecular activity of PdsA: hydrolysis of 3',5'-cyclic AMP (preferred) and cGMP to 5'-nucleotides (EC 3.1.4.35 / 3.1.4.53), acting on the extracellular / cell-surface cAMP pool (UniProt: "Secreted, extracellular space; Cell surface").
• Direct cellular role: clearing secreted cAMP so cAR-mediated relay can oscillate and cells stay responsive during aggregation (PMID:9405107, PMID:23473502). This is genuine negative regulation of a cAMP-receptor (GPCR) / adenylate-cyclase loop — the concept behind Claim A but for a cAMP-activated, not glucose-activated, receptor.
• What is NOT PdsA's direct step: setting the intracellular cAMP concentration that binds PKA regulatory subunits. That is done by RegA (intracellular) and adenylate cyclases (synthesis) (PMID:30790701, PMID:11390363, PMID:36688866). Any PdsA→PKA effect is a downstream / feedback consequence, not a direct transduction step.

Conflicts and Alternatives

• Paralog/ortholog carry-over (primary conflict): both seed terms are IBA from a PANTHER family that pools fungal intracellular glucose-signaling PDEs (S. pombe Pde1/cgs2, C. albicans PDE2) with Dictyostelium secreted PdsA. In fungi those PDEs really do negatively regulate glucose-activated GPCR→cAMP→PKA signaling; the terms are correct there, then over-propagated to PdsA whose biology (extracellular, cAMP-chemoattractant) differs.
• Compartment confusion: the seed hypothesis explicitly asks to separate the extracellular pool (PdsA) from the RegA-controlled intracellular pool — the evidence confirms these are the correct compartment assignments, and the two seed terms conflate them.
• Term-label subtlety: GO:0110034's "glucose-activated" wording could be mistaken for generic "adenylate cyclase-activating GPCR" signaling. Curators should note the qualifier makes it fungal-glucose-specific, so it is not a substitute for the cAMP-receptor role already covered by GO:0007193.

Knowledge Gaps

1. Does PdsA measurably affect intracellular cAMP/PKA in vivo? Checked: literature attributes PKA control to RegA; no assay shows PdsA setting intracellular cAMP. Matters because a genuine (if indirect) effect could justify a regulates-type annotation with an ISS/indirect qualifier — but current evidence favors indirect only. Resolve with: intracellular cAMP / PKA-reporter measurements in pdsA-null vs WT.
2. Is there any Dictyostelium glucose-sensing GPCR→adenylate cyclase pathway? Checked: not described; ACA-activating receptor is cAR1 (cAMP). Matters because GO:0110034 requires it. Resolve with: literature/annotation review confirming absence.
3. RESOLVED (Iteration 2): PMID:17040207 abstract read — it explicitly assigns extracellular-cAMP degradation to DdPDE1 (PdsA) and intracellular-cAMP degradation to DdPDE2 (RegA), confirming the compartment split. Remaining minor gap: the paper is enzyme-kinetics/pool-modeling, so the "IMP" evidence label on GO:0007193/GO:1900115 is curator interpretation; full-text confirmation of the receptor-signaling phenotype would further solidify the retained BP terms.

Discriminating Tests

• pdsA-null vs regA-null, intracellular cAMP + PKA activity time-course: regA-null elevates intracellular cAMP/PKA (precocious development); pdsA-null should not directly elevate the intracellular pool — cleanly separates Claim B ownership.
• 8Br-cAMP / PKA-agonist rescue: rescues intracellular-cAMP/PKA deficits (as in acaA-acrA- double mutants, PMID:36688866) but is not expected to be the axis of pdsA phenotypes (which are extracellular-relay/chemotaxis).
• Ortholog-context check: confirm PANTHER PTN002001416 groups secreted Dictyostelium PDEs with intracellular fungal PDEs — evidence that the IBA propagation crosses a compartment/function boundary and should be blocked for PdsA.

Curation Leads (require curator verification)

• Action: Remove/withhold GO:0110034 and GO:0141162 from pdsA (P12019); both are IBA-only ortholog carry-overs crossing a compartment/pathway boundary. Consider flagging GO:1902660 as non-core.
• Optional replacement (curator-verify): if a receptor-loop BP is desired, use the non-glucose GO:0106072 (negative regulation of adenylate cyclase-activating GPCR signaling pathway), contextualized to the cAMP-receptor pathway GO:0140582 — not the fungal glucose term GO:0110034. Note GO:0043951 is obsolete.
• Reassign: GO:0141162 is appropriate for regA (Q23917), the intracellular cAMP/PKA negative regulator. Primary support: PMID:17040207 — "Intracellular cAMP is degraded by the DdPDE2 [RegA]…" vs "Extracellular cAMP is degraded predominantly by…DdPDE1 [PdsA]".
• Retain: GO:0004115 (MF, IDA), GO:0007193 and GO:1900115 (BP, IMP PMID:17040207) — these already capture PdsA's true negative-regulatory, extracellular role.
• Candidate references / snippets to verify:
• PMID:30790701 — "the intracellular cAMP-specific phosphodiesterase RegA is a negative regulator of…PKA".
• PMID:11390363 — "intracellular cAMP and PKA activity are controlled by…degradation by the cAMP-specific phosphodiesterase RegA".
• PMID:36688866 — adenylate cyclases produce "secreted cAMP for…gene expression and intracellular cAMP for PKA activation".
• PMID:9405107 / PMID:23473502 — PdsA is the secreted extracellular-cAMP PDE governing relay.
• Suggested questions for curator: Should IBA annotations from PANTHER PTN002001416 be suppressed for the secreted Dictyostelium Pds clade? Is a "regulation of adenylate cyclase-activating (cAMP) GPCR signaling" term (non-glucose) already covered by GO:0007193 for this gene?
• Suggested experiments: intracellular cAMP/PKA-reporter assay in pdsA-null vs regA-null to formally exclude any direct PdsA role in the PKA-activating pool.

Limitations

Analysis used public UniProt/QuickGO metadata and PubMed/efetch abstracts; the fungal ortholog primary papers (S. pombe cgs2/Pde1; C. albicans PDE2) were not full-text read. Verdicts on IBA provenance are drawn from curation metadata (evidence code, GO_REF, with-from, PANTHER family PTN002001416) — high confidence — rather than re-derived phylogeny. PMID:17040207 was read at abstract level (Iteration 2) and directly documents the PdsA=extracellular / RegA=intracellular pool split.

Artifacts

• OpenScientist final report
• OpenScientist final report