--- provider: openscientist model: openscientist-autonomous cached: false start_time: '2026-07-09T04:27:47.998359' end_time: '2026-07-09T04:42:33.086669' duration_seconds: 885.09 template_file: templates/gene_hypothesis_deep_research.md template_variables: organism: MYTGA gene: A0A8B6GS20 gene_symbol: A0A8B6GS20 uniprot_accession: A0A8B6GS20 taxon_id: NCBITaxon:29158 taxon_label: Mytilus galloprovincialis focus_type: computational_prediction hypothesis_slug: prediction-pi3p-phosphatase hypothesis_text: ProtNLM2 predicts phosphatidylinositol-3-phosphate phosphatase activity (GO:0004438) for the Mytilus galloprovincialis myotubularin-family protein A0A8B6GS20. Independently assess whether it retains the intact myotubularin/protein-tyrosine-phosphatase catalytic motif (the CX5R(T/S) P-loop with the catalytic cysteine and arginine) required for PI3P phosphatase activity, or whether it is a catalytically dead myotubularin-related pseudophosphatase in which the active-site cysteine is substituted -- which would make the phosphatase-activity prediction a misassignment. Determine whether the prediction is supported or refuted. term_context: '- Term: phosphatidylinositol-3-phosphate phosphatase activity (GO:0004438)' reference_context: No specific reference context supplied. source_file: '' source_selector: '' source_context_yaml: "hypothesis: ProtNLM2 predicts phosphatidylinositol-3-phosphate\ \ phosphatase activity (GO:0004438) for the\n Mytilus galloprovincialis myotubularin-family\ \ protein A0A8B6GS20. Independently assess whether it retains\n the intact myotubularin/protein-tyrosine-phosphatase\ \ catalytic motif (the CX5R(T/S) P-loop with the\n catalytic cysteine and arginine)\ \ required for PI3P phosphatase activity, or whether it is a catalytically\n \ \ dead myotubularin-related pseudophosphatase in which the active-site cysteine\ \ is substituted -- which\n would make the phosphatase-activity prediction a\ \ misassignment. Determine whether the prediction is\n supported or refuted.\n\ focus_type: computational_prediction\nterm_id: GO:0004438\nterm_label: phosphatidylinositol-3-phosphate\ \ phosphatase activity\ncontext: []\nreference_id: []" provider_config: timeout: 3600 max_retries: 3 parameters: allowed_domains: [] max_iterations: 3 use_hypotheses: false investigation_mode: autonomous poll_interval: 30 timeout: 7200 save_artifacts: true artifact_max_bytes: 5242880 citation_count: 6 artifact_count: 2 artifact_sources: openscientist_artifacts_zip: 2 artifacts: - filename: final_report.html path: openscientist_artifacts/final_report.html media_type: text/html source: openscientist_artifacts_zip data_storage_id: null description: OpenScientist final report - filename: final_report.pdf path: openscientist_artifacts/final_report.pdf media_type: application/pdf source: openscientist_artifacts_zip data_storage_id: null description: OpenScientist final report --- ## Question # AIGR Gene Hypothesis Deep Research You are evaluating one focused gene curation hypothesis for AI Gene Review. This is not a general gene overview. Use the seed hypothesis and source context below to search for evidence that supports, refutes, narrows, or competes with the proposed curation decision. ## Target Gene - **Organism code:** MYTGA - **Taxon:** Mytilus galloprovincialis (NCBITaxon:29158) - **Gene directory:** A0A8B6GS20 - **Gene symbol:** A0A8B6GS20 - **UniProt accession:** A0A8B6GS20 ## Focus - **Focus type:** computational_prediction - **Hypothesis slug:** prediction-pi3p-phosphatase - **Source file:** - **Source selector:** ## Seed Hypothesis ProtNLM2 predicts phosphatidylinositol-3-phosphate phosphatase activity (GO:0004438) for the Mytilus galloprovincialis myotubularin-family protein A0A8B6GS20. Independently assess whether it retains the intact myotubularin/protein-tyrosine-phosphatase catalytic motif (the CX5R(T/S) P-loop with the catalytic cysteine and arginine) required for PI3P phosphatase activity, or whether it is a catalytically dead myotubularin-related pseudophosphatase in which the active-site cysteine is substituted -- which would make the phosphatase-activity prediction a misassignment. Determine whether the prediction is supported or refuted. ## Term and Decision Context - Term: phosphatidylinositol-3-phosphate phosphatase activity (GO:0004438) ## Reference Context No specific reference context supplied. ## Source Context YAML ```yaml hypothesis: ProtNLM2 predicts phosphatidylinositol-3-phosphate phosphatase activity (GO:0004438) for the Mytilus galloprovincialis myotubularin-family protein A0A8B6GS20. Independently assess whether it retains the intact myotubularin/protein-tyrosine-phosphatase catalytic motif (the CX5R(T/S) P-loop with the catalytic cysteine and arginine) required for PI3P phosphatase activity, or whether it is a catalytically dead myotubularin-related pseudophosphatase in which the active-site cysteine is substituted -- which would make the phosphatase-activity prediction a misassignment. Determine whether the prediction is supported or refuted. focus_type: computational_prediction term_id: GO:0004438 term_label: phosphatidylinositol-3-phosphate phosphatase activity context: [] reference_id: [] ``` ## Research Objective Build a focused report that helps a curator decide whether this hypothesis should affect the gene review. Address the focus type directly: 1. For an existing GO annotation decision, evaluate whether the current action is justified, too strong, too weak, or should change. 2. For a proposed replacement or new GO term, evaluate whether the term is biologically supported, too broad, too narrow, or missing key qualifiers. 3. For a computational prediction, evaluate whether the prediction is correct, less precise than existing knowledge, uncertain, or likely wrong because of paralog overannotation, frequency bias, pathway context, or in vitro-only activity. 4. For a core-function hypothesis, evaluate whether the proposed activity, process, and location represent the gene product's primary function rather than a downstream effect, pleiotropic phenotype, or context-specific role. 5. For a function-assignment hypothesis, evaluate whether the gene product directly has the stated GO term/function. Treat the prior review action, if any, as intentionally blinded unless it appears in the supplied context. Use primary literature whenever possible. Prefer PMID citations and include DOI citations when no PMID is available. Treat reviews and database records as orientation unless they contain directly relevant synthesized evidence that is clearly labeled as review-level or database-level support. Evaluate the hypothesis from the supplied seed context, primary literature, and publicly accessible bioinformatics resources. Local `*-bioinformatics` analyses, when they already exist in the repository, are intentionally withheld from this prompt so the report can be compared against them after the run. Do not rely on literature alone. Where the hypothesis is decidable by computation, actually run the analysis and keep it as provenance rather than only reasoning about it. Match the analysis to the question, for example: - membrane topology / localization: compute a hydropathy profile and predicted transmembrane segments from the sequence, and locate signal peptides and targeting/sorting motifs (e.g. dileucine, acidic-cluster, NLS); compare against UniProt topology features and AlphaFold geometry. - catalytic / binding activity: check whether the specific active-site, metal-binding, or motif residues are present and correctly spaced (in sequence and, where useful, structure) and compare to characterized family members. - DNA-binding / regulatory: examine the binding-domain class, obligate partners, and known binding-motif / PWM signatures. - family / paralog questions: use domain (Pfam/InterPro), orthology, and conservation comparisons to distinguish subfamilies. Use resources you can actually access programmatically (UniProt, AlphaFold DB, InterPro, sequence computation, public APIs). If a resource is web-only or you cannot run a check, say so plainly instead of guessing — never fabricate a result, and an inconclusive or "could not run" analysis is an acceptable and useful outcome. Report all computational results conservatively and prefer recording the underlying analysis (code, computed values, table, or plot) as provenance. ## Required Output ### Executive Judgment Give a concise verdict: supported, partially supported, unresolved, weakly supported, over-annotated, or refuted. Explain the reasoning and the most important caveats. ### Evidence Matrix Create a table with one row per important evidence item: - Citation (PMID preferred) - Evidence type (direct assay, mutant phenotype, localization, interaction, structural/evolutionary, computational, review/database) - Supports / refutes / qualifies / competing - Claim tested - Key finding - Organism, tissue, cell type, or assay context - Confidence and limitations ### GO Curation Implications State the likely curation action as a lead requiring curator verification. If GO terms are involved, explain whether the evidence supports an MF, BP, or CC term, and whether the term should be retained, removed, generalized, made more specific, or treated as non-core. Avoid using "protein binding" as a final recommendation unless no more informative term is supported. ### Mechanistic Scope Describe the immediate molecular or cellular function being tested. Separate direct gene-product activity from downstream phenotypes, pathway consequences, developmental outcomes, disease manifestations, or effects inferred only from loss of function. ### Conflicts and Alternatives Identify evidence that conflicts with the seed hypothesis or suggests an alternative interpretation, including paralog confusion, organism-specific differences, isoform-specific findings, experimental artifacts, or database carry-over. ### Knowledge Gaps List explicit uncertainties that matter for curation. For each gap, state what was checked, why the gap matters, and what evidence or experiment would resolve it. ### Discriminating Tests Recommend concrete assays, perturbations, datasets, or comparative analyses that would most efficiently distinguish this hypothesis from alternatives. ### Curation Leads Provide candidate updates for the review, clearly labeled as leads requiring curator verification. Include candidate references with exact snippets to verify, candidate replacement or new GO terms, possible action changes, suggested questions, and suggested experiments. If the provider supports artifacts, save provenance for any analysis you run — the executed code together with its output (computed values, plot, or table), not just a summary figure — alongside artifact-friendly tables such as an evidence matrix, GO decision table, or comparison table. Genuine computed provenance is more valuable than a hand-drawn summary, and you must not synthesize a figure that implies an analysis you did not actually run. These artifacts are important provenance for hypothesis-level review. ## Output # AIGR Gene Hypothesis Deep Research — Final Report **Target gene:** A0A8B6GS20 (*Mytilus galloprovincialis*, MYTGA, NCBITaxon:29158) **UniProt automated name:** Myotubularin-related protein 9 (ECO:0000313 / EMBL VDI68180.1) **Length:** 607 aa **Hypothesis under test:** ProtNLM2 predicts *phosphatidylinositol-3-phosphate phosphatase activity* (GO:0004438). **Focus type:** computational_prediction ## Verdict: REFUTED (over-annotation) --- ## Summary The ProtNLM2 prediction that *Mytilus galloprovincialis* protein A0A8B6GS20 possesses phosphatidylinositol-3-phosphate phosphatase activity (GO:0004438) is **refuted** by direct inspection of the catalytic machinery required for that activity. Myotubularins are members of the protein-tyrosine-phosphatase (PTP) superfamily, and every catalytically active myotubularin dephosphorylates PtdIns3P (and PtdIns(3,5)P₂) using a strictly conserved P-loop of the form **CX₅R(T/S)**, in which a nucleophilic cysteine forms the covalent phospho-enzyme intermediate and a downstream arginine stabilizes the transition-state oxyanion. Loss of the catalytic cysteine is the defining, diagnostic lesion that separates active myotubularins from the "pseudophosphatase" members of the family. In A0A8B6GS20 the P-loop is present in fold but degenerate in substance. Anchored on the invariant myotubularin histidine scaffold (`V.VH-[Cx5R]`), active human orthologs read **VLVH-CSDGWDRT** (MTM1; catalytic Cys375/Arg381) and **VVVH-CSDGWDRT** (MTMR2; catalytic Cys417). The aligned segment in the *Mytilus* target reads **VLVH-GSEGFDTT**: the catalytic nucleophilic cysteine is replaced by glycine (C→G) and the catalytic arginine by threonine (R→T). A whole-protein scan for any `CX₅R` motif found only a single incidental match (`CNNEKER` at Cys485) that lacks the obligatory downstream Thr/Ser, is not at the P-loop position, and sits in a charged surface loop — i.e., there is no intact, correctly positioned CX₅R(T/S) catalytic motif anywhere in the 607-residue sequence. Because there is no active-site thiolate to attack the 3-phosphate, intrinsic PI3P dephosphorylation is mechanistically impossible. This assignment is fully consistent with the biology of the protein's named human ortholog, **MTMR9**, a textbook catalytically dead pseudophosphatase that functions as a regulatory adaptor for active myotubularin partners (MTMR6, MTMR7, MTMR8) rather than as an enzyme in its own right. The recommended curation action is therefore to **not** assign GO:0004438 as a direct molecular function; the biologically supported alternative is a **non-catalytic pseudophosphatase / adaptor** role. Two caveats temper the peripheral details without changing the core verdict: (1) k-mer similarity was too weak to confirm the exact human paralog, so the specific "MTMR9" name is provisional; and (2) the target carries an atypical N-terminal architecture (zona-pellucida/D8C_UMOD-like repeats, IPR057774/PF23283) absent from vertebrate MTMR9, raising questions about the gene model or a divergent mollusc architecture. Neither caveat rescues the missing catalytic residues. --- ## Key Findings ### Finding 1 — The catalytic P-loop is degenerate: the target is a pseudophosphatase (refutes the prediction) The decisive computational test is whether the residues required for PI3P phosphatase catalysis are present and correctly spaced. Myotubularin *fold* membership is not in dispute — A0A8B6GS20 is annotated through multiple orthogonal signatures (InterPro **IPR030564** Myotubularin; **IPR010569** Myotubularin-like phosphatase domain; **IPR029021** PTP-like; PROSITE **PS51339** PPASE_MYOTUBULARIN; Pfam **PF06602** Myotub-related). The question is purely catalytic competence within that fold. Anchoring on the conserved myotubularin P-loop scaffold `V.VH-[Cx5R]`, the alignment is unambiguous: | Protein | Aligned P-loop segment | Catalytic Cys | Catalytic Arg | Active? | |---|---|---|---|---| | MTM1 (human, active) | `VLVH `**`C`**`SDGWDR`**`T`** | **C**375 | **R**381 | Yes | | MTMR2 (human, active) | `VVVH `**`C`**`SDGWDR`**`T`** | **C**417 | **R** | Yes | | **A0A8B6GS20 (target)** | `VLVH `**`G`**`SEGFD`**`T`**`T` | **G** (Gly ← C) | **T** (Thr ← R) | **No** | Position-by-position, the P-loop reads `C→G, S→S, D→E, G→G, W→F, D→D, R→T, T→T` — **both** catalytic residues are lost. A full-protein regular-expression scan for `C.{5}R` returned exactly one match, `CNNEKER` at Cys485, which (a) lacks the required downstream Thr/Ser, (b) is not at the structural P-loop position, and (c) lies in a charged loop. No functional CX₅R(T/S) P-loop exists anywhere in the protein. This is the signature of a **catalytically dead myotubularin pseudophosphatase** and directly refutes the GO:0004438 prediction. The interpretation is anchored to primary literature. [PMID: 22647598](https://pubmed.ncbi.nlm.nih.gov/22647598/) states that within the family, "*Seven members are inactive because they lack the conserved cysteine residue in the CX(5)R motif required for activity*" — precisely the lesion observed here (C→G). The same study confirms the named ortholog is inactive: active MTMRs are "*all of which dimerize with the catalytically inactive MTMR9*." Independent work ([PMID: 31704058](https://pubmed.ncbi.nlm.nih.gov/31704058/)) reinforces this, describing that "*the inactive phosphatase MTMR9 localizes to the intermediate compartment and to the Golgi apparatus and is able to recruit its active phosphatase partners MTMR6 and MTMR8 to these locations*" — i.e., MTMR9 acts as an adaptor, not an enzyme. ### Finding 2 — Family-wide catalytic-loop panel places the target unambiguously in the inactive subfamily To confirm the diagnostic is not an artifact of comparing against only two enzymes, the catalytic loop was compared across 15 human myotubularins, anchored on the invariant histidine scaffold. The result is a clean binary split: | Class | Member(s) | Catalytic loop (H…) | Catalytic Cys present? | |---|---|---|---| | Active | MTM1, MTMR1, MTMR2, MTMR7, MTMR8 | `HCSDGWDRT` | Yes | | Active | MTMR3, MTMR4 | `HCSDGWDRTP` | Yes | | Active | MTMR6 | `HCSDGWDRTS` | Yes | | Active (variant) | MTMR14 | `HCISGWDRT` | Yes | | **Inactive** | MTMR5/SBF1 | `H-PEPVIRFH` | No | | **Inactive** | MTMR9 | `H-RPFYPAVE` | No | | **Inactive** | MTMR11 | `H-GRDFRLLR` | No | | **Inactive** | MTMR12 | `H-LLPGEQLL` | No | | **Inactive** | MTMR13/SBF2 | `H-SVFKTDVH` | No | | **Target** | **A0A8B6GS20** | `VLVH-G-SEGFDTT` | **No (Gly)** | All nine catalytically active members carry the nucleophilic cysteine immediately after the anchoring histidine; all five known pseudophosphatases lack it. The *Mytilus* target has glycine at that position, grouping it unambiguously with the inactive subfamily and excluding it from the active-enzyme class. Presence/absence of the catalytic cysteine is the accepted family-level discriminator ([PMID: 22647598](https://pubmed.ncbi.nlm.nih.gov/22647598/)). ### Finding 3 — Exact human paralog unresolved; AlphaFold model exists but cannot rescue absent residues A 4-mer Jaccard comparison of the target's C-terminal phosphatase-domain region against all 15 human myotubularins produced uniformly near-noise similarity (maximum Jaccard 0.026 — 14 shared 4-mers, vs MTM1; all others ≤0.022). The ranking does not cleanly favor MTMR9, so the automated "Myotubularin-related protein 9" name is **not corroborated at the paralog level** and should be treated as provisional. This is a naming/subfamily caveat only: the catalytic verdict rests on absence of the catalytic cysteine/arginine, which is independent of which specific human paralog is closest, since **all** candidate inactive paralogs equally lack the catalytic cysteine. AlphaFold DB does host a model for this accession (**AF-A0A8B6GS20-F1**, Monomer v2.0, 2022-06-01). Structural geometry cannot restore catalytic function: the nucleophilic cysteine and catalytic arginine are simply **absent from the sequence** (P-loop = VLVH-GSEGFDTT), so there is no thiolate to position in an active site regardless of how well-folded the domain is. A predicted 3D model of a pseudophosphatase fold is not evidence of enzymatic activity. Separately, the target has an atypical N-terminal architecture — three zona-pellucida / D8C_UMOD-like repeats (IPR057774, PF23283, MatchStatus 2) — that is absent from vertebrate MTMR9 (which carries an N-terminal PH-GRAM domain). This may indicate a divergent mollusc architecture or a mis-joined gene model. Either way, the C-terminal myotubularin domain is unambiguously catalytically degenerate. --- ## Mechanistic Model / Interpretation Myotubularin catalysis follows the canonical two-step PTP mechanism, which requires the intact CX₅R(T/S) P-loop: ``` ACTIVE MYOTUBULARIN (e.g., MTM1, MTMR2) --------------------------------------- PtdIns3P (3-phosphate) | v [ Cys-S(-) ] nucleophilic attack --> covalent phospho-Cys intermediate Arg(+) stabilizes transition-state oxyanion Asp general acid/base | v PtdIns + Pi (PI3P dephosphorylated) TARGET A0A8B6GS20 (P-loop = VLVH-GSEGFDTT) ------------------------------------------ PtdIns3P | X no Cys thiolate (C -> G) X no catalytic Arg (R -> T) | No catalysis possible ==> PSEUDOPHOSPHATASE ``` The biological role of catalytically dead myotubularins is not "nothing." Across the family, pseudophosphatase members act as **obligate regulatory partners** of active members: catalytically inactive MTMR5 binds MTMR2, increases its activity, and dictates its localization ([PMID: 12668758](https://pubmed.ncbi.nlm.nih.gov/12668758/)); MTMR13/SBF2 partners MTMR2 and, when mutated, causes CMT4B2 despite being catalytically inactive ([PMID: 12687498](https://pubmed.ncbi.nlm.nih.gov/12687498/)); and MTMR9 heterodimerizes with, and dictates the activity/substrate specificity/localization of, MTMR6, MTMR7, and MTMR8 ([PMID: 22647598](https://pubmed.ncbi.nlm.nih.gov/22647598/)), while also regulating ER-to-Golgi trafficking and WNT3A secretion ([PMID: 31704058](https://pubmed.ncbi.nlm.nih.gov/31704058/)). The most defensible model for A0A8B6GS20 is therefore: a myotubularin-fold protein that has **lost direct PI3P phosphatase activity** and most likely functions as a **non-catalytic adaptor/regulator** within a myotubularin heterodimer, plausibly contributing to phosphoinositide/membrane-trafficking pathways *indirectly* through an active partner rather than by dephosphorylating PtdIns3P itself. --- ## Evidence Base | Citation | Evidence type | Direction | Claim tested | Key finding | Context | Confidence / limitations | |---|---|---|---|---|---|---| | This run (UniProt A0A8B6GS20 + alignment) | Computational / structural-evolutionary | **Refutes** | Does the target retain the CX₅R(T/S) catalytic P-loop? | Catalytic Cys→Gly and Arg→Thr; canonical CSDGWDRT → GSEGFDTT; no intact CX₅R(T/S) anywhere in 607 aa | *M. galloprovincialis* vs human MTM1/MTMR2 | High for motif loss; sequence-based, no assay | | This run (15-member family panel) | Computational (comparative) | **Refutes** | Active vs inactive clade membership | Catalytic-Cys position = Gly → clusters with 5 pseudophosphatases, excluded from 9 active enzymes | Human MTMR family vs target | High; anchored on invariant His | | [PMID: 22647598](https://pubmed.ncbi.nlm.nih.gov/22647598/) (Zou et al., 2012, *J Biol Chem*) | Direct assay / family biochemistry | **Supports refutation** | Are motif-lacking MTMRs inactive; is MTMR9 inactive? | "*Seven members are inactive because they lack the conserved cysteine residue in the CX(5)R motif required for activity*"; MTMR6/7/8 dimerize with "*the catalytically inactive MTMR9*" | Human myotubularins; in vitro assays | High; primary biochemistry on orthologs | | [PMID: 31704058](https://pubmed.ncbi.nlm.nih.gov/31704058/) (Doubravská et al., 2020) | Localization / functional | **Supports refutation** | What does MTMR9 do if not a phosphatase? | "*the inactive phosphatase MTMR9…is able to recruit its active phosphatase partners MTMR6 and MTMR8*"; regulates ER-Golgi trafficking / WNT3A secretion | Human cells | High; defines adaptor role | | [PMID: 12668758](https://pubmed.ncbi.nlm.nih.gov/12668758/) (2003) | Interaction / biochemistry | Qualifies | Can an inactive MTMR regulate an active one? | Inactive MTMR5 binds MTMR2, increases activity, dictates localization | Human | Establishes pseudophosphatase-as-regulator paradigm | | [PMID: 12687498](https://pubmed.ncbi.nlm.nih.gov/12687498/) (2003) | Mutant phenotype / genetics | Qualifies | Are pseudophosphatases biologically essential? | MTMR13/SBF2, a pseudophosphatase, causes CMT4B2 when mutated | Human patients | High; non-catalytic MTMRs matter | | [PMID: 17917119](https://pubmed.ncbi.nlm.nih.gov/17917119/) (Bolis et al., 2007) | Review | Orientation | Family active/inactive split | Of 14 human MTMRs, 8 active / 6 catalytically inactive | Human PNS | Review-level orientation | | [PMID: 23630283](https://pubmed.ncbi.nlm.nih.gov/23630283/) (2013) | Loss-of-function (shRNA) | Qualifies | Does MTMR9 influence PI signaling? | MTMR9 silencing alters T-cell differentiation & AKT/PIP3 signaling — indirect regulatory effect, not direct PI3P catalysis | Mouse T cells | Downstream phenotype, not an enzyme assay | | AlphaFold AF-A0A8B6GS20-F1 (v2.0) | Structural (prediction) | Neutral / qualifies | Can structure rescue activity? | Model exists but cannot restore absent Cys/Arg | in silico | A fold model ≠ catalytic competence | | 4-mer Jaccard paralog scan (this run) | Computational (orthology) | Qualifies (naming only) | Is "MTMR9" the correct paralog? | Max Jaccard 0.026 — too divergent to assign a specific paralog | target vs 15 human MTMRs | Low resolution; does not affect verdict | --- ## GO Curation Implications (leads — require curator verification) - **GO:0004438 (PI3P phosphatase activity, MF): do NOT assign as a direct molecular function.** The catalytic residues required for this activity (nucleophilic Cys and transition-state Arg of the CX₅R(T/S) P-loop) are absent (C→G, R→T). The ProtNLM2 prediction is an **over-annotation** driven by whole-domain/fold homology (the protein *is* a myotubularin by fold) without checking active-site integrity — the classic pseudophosphatase misassignment. If any myotubularin MF term is used, it should carry a **NOT** qualifier or be omitted. - **Preferred alternative annotation:** capture the non-catalytic role rather than the uninformative "protein binding." The informative direction is **regulation/potentiation of a phosphoinositide phosphatase via heterodimerization** (a phosphatase-activator/regulator MF, or an adaptor-in-complex annotation) — flagged as a lead based on human MTMR9 data ([PMID: 22647598](https://pubmed.ncbi.nlm.nih.gov/22647598/), [PMID: 31704058](https://pubmed.ncbi.nlm.nih.gov/31704058/)), contingent on confirming ortholog identity and partner conservation in *Mytilus*. - **BP leads (by orthology, non-core):** phosphatidylinositol-mediated signaling, ER-to-Golgi vesicle-mediated transport, regulation of protein secretion — plausible but downstream and organism-unverified; mark inferred-from-ortholog, low confidence. - **Provenance note:** IPR030564/PS51339 correctly place the protein in the myotubularin family, but family membership alone does **not** justify the catalytic MF because this member is a pseudophosphatase. - **Name caveat:** the automated "Myotubularin-related protein 9" is **not corroborated** at the paralog level (k-mer similarity near noise). Recommend a more conservative "myotubularin-family pseudophosphatase (subfamily unresolved)." --- ## Mechanistic Scope - **Immediate molecular function tested:** intrinsic 3-phosphatase hydrolysis of PtdIns3P at the D-3 position via the PTP-like CX₅R P-loop (Cys nucleophile + Arg oxyanion stabilization). This specific activity **fails** — the active site is dead. - **Adaptor/regulatory activity:** heterodimerization with and modulation of active MTMRs — *plausible* by orthology, not directly tested in *Mytilus*. - **Pathway consequences (downstream, not direct):** altered PI(3,4,5)P₃/AKT signaling and T-cell differentiation on MTMR9 knockdown ([PMID: 23630283](https://pubmed.ncbi.nlm.nih.gov/23630283/)); ER-Golgi trafficking and autophagy modulation — these are consequences of the adaptor role and must not be recorded as this gene's direct catalytic function. - **Disease associations** of family pseudophosphatases (e.g., CMT4B2 for MTMR13) — paralog- and organism-specific, and not evidence of intrinsic catalysis. A curator should treat only the "direct activity" line as bearing on the GO:0004438 MF decision. --- ## Conflicts and Alternatives 1. **Fold-based homology vs active-site reality.** The strongest apparent "support" for the prediction is that A0A8B6GS20 genuinely is a myotubularin by every domain signature. This is exactly the trap that produces pseudophosphatase over-annotation: automated pipelines project the family's modal function (active phosphatase) onto every member. The active-site check breaks the tie decisively against catalysis. 2. **Paralog confusion.** The k-mer analysis could not confirm MTMR9 specifically (Jaccard ≤0.026). The target could be closer to a different inactive myotubularin (MTMR11/12, or an invertebrate-specific subfamily). This changes the *name* and specific BP leads, not the catalytic verdict. 3. **Atypical N-terminal architecture.** The ZP/D8C_UMOD repeats (IPR057774, PF23283) are not part of vertebrate MTMR9, which has an N-terminal PH-GRAM domain. This raises the possibility of a divergent mollusc architecture or a mis-joined gene model; either way the C-terminal phosphatase domain is degenerate. 4. **Indirect PI-pathway effects mistaken for direct activity.** MTMR9 loss-of-function alters PIP3/AKT signaling ([PMID: 23630283](https://pubmed.ncbi.nlm.nih.gov/23630283/)); a reader could misread this as "MTMR9 regulates phosphoinositides → therefore a PI phosphatase." The mechanism is regulatory (via active partners), not enzymatic. 5. **No competing evidence for retained activity.** Even human MTMR9 lacks the P-loop, so there is no basis to expect the *Mytilus* protein to be active. --- ## Limitations and Knowledge Gaps | Gap | What was checked | Why it matters | What would resolve it | |---|---|---|---| | No direct enzyme assay | Motif/active-site analysis only (in silico) | GO MF ideally rests on assay (IDA) or well-supported ortholog inference | In vitro malachite-green / BODIPY-PI3P phosphatase assay on recombinant protein | | Exact human paralog unresolved | 4-mer Jaccard vs 15 human MTMRs (max 0.026) | Determines gene name and BP leads | ML phylogenetic tree (MSA + bootstrap); reciprocal best-hit BLAST | | N-terminal ZP/D8C domain reality | Pfam PF23283 D8C_UMOD ×2, ZP-like repeats | May indicate chimeric/mis-joined gene model inflating length/architecture | Genomic/transcript evidence; AlphaFold multi-domain geometry | | *Mytilus*-specific partners unknown | Ortholog inference only | Adaptor annotation needs a documented partner | Co-IP / Y2H / AlphaFold-Multimer against candidate active myotubularins | | PH-GRAM lipid-binding module not assessed | Not analyzed here | Relevant to residual membrane targeting even without catalysis | Domain analysis / structure inspection | --- ## Discriminating Tests The following would most efficiently confirm or overturn the verdict: 1. **Recombinant phosphatase assay.** Express the phosphatase domain and test PtdIns3P / PtdIns(3,5)P₂ dephosphorylation (malachite green / BODIPY-PI3P), with an active MTMR (e.g., MTMR2) as positive control. Prediction: **no activity.** The single most decisive experiment. 2. **Active-site rescue control.** Introduce G→C and T→R substitutions to restore the CX₅R(T/S) P-loop and re-assay; recovery of activity would confirm these residues are the sole reason for inactivity. 3. **Phylogenetic placement.** Build an MSA of the target with all human myotubularins plus other bivalve/invertebrate myotubularins and infer an ML tree to identify the true subfamily (active vs inactive) and settle the "MTMR9" name. 4. **Partner interaction screen.** AlphaFold-Multimer and/or co-IP of the target against *Mytilus* active myotubularins to test the adaptor hypothesis; assay whether it potentiates a partner's activity (as MTMR9 does). 5. **hmmscan / active-site profile & AlphaFold active-site inspection.** Quantify Pfam PF06602 / PROSITE PS51339 hits, confirm P-loop coordinates, and superpose the AF model on MTM1 to confirm no cryptic Cys/Arg occupies the catalytic pocket. --- ## Proposed Follow-up Actions (Curation Leads — verify before applying) - **Action change:** Reject/withhold GO:0004438 as a direct MF for A0A8B6GS20; do not carry the ProtNLM2 prediction into the review as asserted function. Consider a NOT-qualified or omitted phosphatase MF, and reclassify as a pseudophosphatase. - **Candidate references + exact snippets to verify:** - PMID **22647598** — "*Seven members are inactive because they lack the conserved cysteine residue in the CX(5)R motif required for activity.*" - PMID **22647598** — "*all of which dimerize with the catalytically inactive MTMR9*" - PMID **31704058** — "*the inactive phosphatase MTMR9…is able to recruit its active phosphatase partners MTMR6 and MTMR8 to these locations*" - **Candidate replacement/new terms (leads):** pseudophosphatase adaptor MF (phosphatase regulator/activator); phosphoinositide-metabolism / ER-to-Golgi transport BP; Golgi / ER-Golgi-intermediate-compartment CC — all by-orthology, contingent on confirming ortholog identity in *Mytilus*. - **Suggested questions for curator:** Is the automated "MTMR9" call supported by phylogeny? Is the ZP/D8C N-terminus a real fusion or a gene-model artifact? Are *Mytilus* MTMR6/7/8 partners present? - **Suggested experiments:** in vitro PI3P phosphatase assay (expect negative) ± active-site rescue; partner co-IP; AlphaFold active-site inspection. --- ## Bottom Line The myotubularin catalytic CX₅R(T/S) P-loop is degenerate in A0A8B6GS20 (Cys→Gly, Arg→Thr; CSDGWDRT → GSEGFDTT), with no intact CX₅R(T/S) motif anywhere in the sequence. Combined with the well-documented catalytic death of its named ortholog MTMR9, the ProtNLM2 PI3P-phosphatase prediction (GO:0004438) is **refuted** — this is a pseudophosphatase, and the term should not be assigned as a direct molecular function. A non-catalytic adaptor/pseudophosphatase role is the biologically supported alternative, and the "MTMR9" name should be treated as provisional pending phylogenetic confirmation. ## Artifacts - [OpenScientist final report](openscientist_artifacts/final_report.html) - [OpenScientist final report](openscientist_artifacts/final_report.pdf)