ARBA00045851

id: ARBA00045851
description: 'Annotates MORN repeat-containing proteins, specifically MORN3 family members, with function involving p53 regulation through assembly of a suppression complex that tethers SIRT1 and MDM2'
status: COMPLETE
rule_type: ARBA
rule:
  rule_id: ARBA00045851
  condition_sets:
  - number: 1
    conditions:
    - condition_type: INTERPRO
      value: IPR003409
      label: MORN repeat
    - condition_type: INTERPRO
      value: IPR052472
      label: MORN repeat-containing protein 3
    - condition_type: PANTHER
      value: PTHR46511:SF1
  - number: 2
    conditions:
    - condition_type: FUNFAM
      value: 2.20.110.10:FF:000026
      label: MORN repeat containing 3
    - condition_type: TAXON
      value: NCBITaxon:2759
      label: Eukaryota
  go_annotations: []
  # Note: This rule provides only FUNCTION annotation, no GO terms
  entries: []
  reviewed_protein_count: 0
  unreviewed_protein_count: 1802
  created_date: '2024-08-14'
  modified_date: '2025-03-21'
review_summary: 'This ARBA rule provides a highly specific functional annotation for MORN3 proteins based on experimentally characterized human and mouse orthologs. While the molecular mechanism described (p53 regulation via SIRT1/MDM2 tethering) is well-supported for MORN3, applying this specific function broadly to 1802 unreviewed proteins raises concerns about over-annotation. For example, Drosophila protein A1ZB08 (FBgn0034281) was flagged in go-annotation#6179 as an inappropriate annotation target, since this fly gene is not well-expressed in testis and likely does not participate in the mammalian p53/SIRT1/MDM2 pathway. The rule would benefit from additional constraints or a more conservative taxonomic scope given the limited experimental evidence across diverse species.'
action: MODIFY
action_rationale: 'The core biological function is accurate for MORN3 proteins, but the annotation is too specific to apply broadly to all proteins matching these domain patterns. The function description assumes conservation of the specific p53/SIRT1/MDM2 regulatory mechanism across all eukaryotes, which may not be warranted. Recommend either: (1) restricting taxonomic scope to mammals/vertebrates where p53 regulation is well-established, or (2) generalizing the function description to focus on the broader MORN repeat-mediated protein complex assembly role rather than the specific p53 pathway.'
suggested_modifications:
- 'Restrict taxonomic scope to Mammalia (NCBITaxon:40674) or Vertebrata (NCBITaxon:7742) where p53 regulation pathways are well-conserved'
- 'OR generalize function description to: "May function in protein complex assembly through MORN repeat domains, potentially involved in regulatory processes"'
- 'Add taxonomic qualifiers like "in mammals" to the specific p53/SIRT1/MDM2 mechanism description'
parsimony:
  assessment: ACCEPTABLE
  notes: 'The two condition sets provide complementary approaches to identifying MORN3 proteins - one using InterPro domains + PANTHER subfamily, the other using CATH FunFam with taxonomic restriction. Some redundancy exists but may capture different annotation perspectives.'
literature_support:
  assessment: MODERATE
  notes: 'The specific p53 regulation mechanism is well-documented for human and mouse MORN3, but evidence for conservation across all eukaryotes is limited. InterPro entry IPR052472 cites key papers establishing the SIRT1/MDM2 tethering mechanism.'
  supported_by:
  - reference_id: 'InterPro:IPR052472'
    supporting_text: 'Human MORN3 is involved in the regulation of the tumor suppressor p53/TP53 through the assembly of a Morn3-mediated protein complex (referred to as suppresome). MORN3 functions by tethering the enzymes SIRT1 and MDM2 to p53/TP53, leading to its deacetylation-mediated functional inactivation and ubiquitination-dependent degradation [PUB00163406].'
condition_overlap:
  assessment: MINOR
  notes: 'Both condition sets should identify the same MORN3 protein family, but use different domain classification systems (InterPro vs CATH). The overlap is expected and appropriate for robust identification.'
  supported_by: []
go_specificity:
  assessment: TOO_NARROW
  notes: 'This rule provides a free-text FUNCTION comment rather than GO terms. The function description itself is overly specific for the broad taxonomic scope: it describes a mammal-specific p53/SIRT1/MDM2 mechanism that cannot be assumed to be conserved across all eukaryotes matching the domain conditions.'
  supported_by: []
taxonomic_scope:
  assessment: TOO_BROAD
  notes: 'Restricting to Eukaryota is too broad given that the specific p53/SIRT1/MDM2 regulatory mechanism is primarily characterized in mammals. Many eukaryotes may lack these pathway components or have different regulatory mechanisms.'
  supported_by:
  - reference_id: 'PMID:25248657'
    supporting_text: 'Our studies suggest that MORN3 is a novel regulator for spermatogenesis, probably together with MEIG1.'
  - reference_id: 'go-annotation#6179'
    supporting_text: 'Drosophila protein A1ZB08 (FBgn0034281) flagged as inappropriate annotation target; not well-expressed in testis, unlikely to share MORN3 function.'
confidence: 0.4
references:
- id: 'PMID:29681526'
  title: 'A Designed Peptide Targets Two Types of Modifications of p53 with Anti-cancer Activity'
  findings:
  - statement: 'Establishes the MORN3-mediated suppression complex (suppresome) that tethers SIRT1 and MDM2 to p53 for deacetylation and ubiquitination'
- id: 'PMID:25248657'
  title: 'Characterization of membrane occupation and recognition nexus repeat containing 3, meiosis expressed gene 1 binding partner, in mouse male germ cells'
  findings:
  - statement: 'Mouse MORN3 is involved in regulation of spermatogenesis'
- id: 'PMID:35568981'
  title: 'Membrane occupation and recognition nexus (MORN) motif controls protein localization and function.'
  findings:
  - statement: 'MORN repeat-containing proteins are not well-characterized; cited in go-annotation#6179 regarding over-annotation concerns'
- id: 'InterPro:IPR052472'
  title: MORN repeat-containing protein 3 InterPro entry
  findings:
  - statement: 'MORN3 assembles suppression complex tethering SIRT1 and MDM2 to p53 for deacetylation and ubiquitination'
- id: 'InterPro:IPR003409'
  title: MORN repeat InterPro entry
  findings:
  - statement: 'MORN repeats are lipid-binding modules composed of β-hairpin structures'
- id: 'go-annotation#6179'
  title: 'ARBA2GO issue: ARBA00045851 inappropriate annotation of Drosophila MORN3'
  findings:
  - statement: 'Drosophila FBgn0034281 (A1ZB08) flagged as incorrectly annotated with mammal-specific MORN3 function'