aac6-Ib

id: A0A076UB44
gene_symbol: aac6-Ib
aliases:
- "AAC(6')-Ib8"
- "AAC(6')-I"
- Aminoglycoside N(6')-acetyltransferase type 1
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:550
  label: Enterobacter cloacae
description: >-
  AAC(6')-Ib8 is an aminoglycoside 6'-N-acetyltransferase (EC 2.3.1.82) of the GNAT acetyltransferase
  superfamily. It transfers an acetyl group from acetyl-CoA to the 6'-amino group of 4,6-disubstituted
  aminoglycosides (e.g. kanamycin, amikacin, tobramycin, netilmicin), abolishing their binding to the
  16S rRNA A-site and conferring aminoglycoside resistance by drug inactivation. AAC(6')-Ib is the most
  prevalent aminoglycoside acetyltransferase in Gram-negative clinical isolates and is typically carried
  as a gene cassette in class 1 integrons on plasmids; numbered allelic variants (here -Ib8) differ by
  point substitutions.
references:
- id: PMID:18710261
  title: "Mechanistic and structural analysis of aminoglycoside N-acetyltransferase AAC(6')-Ib and its bifunctional, fluoroquinolone-active AAC(6')-Ib-cr variant."
  findings:
  - statement: >-
      AAC(6')-Ib is a regioselective aminoglycoside N-acetyltransferase; such enzymes are the
      predominant cause of bacterial aminoglycoside resistance. It acetylates the 6'-amino group, with
      Asp115 acting as the general base.
    supporting_text: "Enzymatic modification of aminoglycoside antibiotics mediated by regioselective aminoglycoside N-acetyltransferases is the predominant cause of bacterial resistance to aminoglycosides."
  - statement: >-
      AAC(6')-Ib-wt was expressed and purified as a soluble protein and its three-dimensional structure
      solved in complex with donor (CoA) and acceptor (aminoglycoside) ligands, defining the catalytic
      mechanism.
    supporting_text: "The three-dimensional structure of AAC(6')-Ib-wt was determined in various complexes with donor and acceptor ligands to resolutions greater than 2.2"
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified (Vetting et al., Biochemistry 2008; PMC2855648, full text). Kinetic and structural
      characterization of AAC(6')-Ib (and the -cr variant); directly supports the 6'-N-acetyltransferase
      activity and the soluble GNAT-fold enzyme.
- id: PMID:16369542
  title: "Fluoroquinolone-modifying enzyme: a new adaptation of a common aminoglycoside acetyltransferase."
  findings:
  - statement: >-
      A variant of AAC(6')-Ib (AAC(6')-Ib-cr, bearing Trp102Arg and Asp179Tyr) acquires the ability to
      N-acetylate fluoroquinolones (ciprofloxacin), reducing their activity.
    supporting_text: "ciprofloxacin in clinical bacterial isolates conferred by a variant of the gene encoding aminoglycoside acetyltransferase AAC(6')-Ib"
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified (Robicsek et al., Nat Med 2006). Describes the AAC(6')-Ib-cr fluoroquinolone-active
      variant; relevant to whether this allele (-Ib8) is a classical aminoglycoside-only enzyme.
- 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:0000104
  title: "Gene Ontology annotation by UniProt keywords"
  findings: []
- id: GO_REF:0000117
  title: "Electronic Gene Ontology annotations created by ARBA machine learning models"
  findings: []
existing_annotations:
- term:
    id: GO:0016407
    label: acetyltransferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000104
  qualifier: enables
  review:
    summary: >-
      Correct but over-general. The specific characterised activity is aminoglycoside
      6'-N-acetyltransferase activity (GO:0047663, EC 2.3.1.82), which is already annotated.
    action: MODIFY
    reason: >-
      Over-general parent of the specific GO:0047663 already present on this entry; the specific term
      should be used.
    proposed_replacement_terms:
    - id: GO:0047663
      label: aminoglycoside 6'-N-acetyltransferase activity
- term:
    id: GO:0016740
    label: transferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000104
  qualifier: enables
  review:
    summary: >-
      Root-level transferase term derived from the UniProt 'Transferase' keyword; uninformative given
      the specific GO:0047663 annotation.
    action: MODIFY
    reason: >-
      Far too general (keyword-derived); subsumed by the specific aminoglycoside 6'-N-acetyltransferase
      activity.
    proposed_replacement_terms:
    - id: GO:0047663
      label: aminoglycoside 6'-N-acetyltransferase activity
- term:
    id: GO:0016747
    label: acyltransferase activity, transferring groups other than amino-acyl groups
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      Correct but over-general (InterPro-derived); the specific 6'-N-acetyltransferase activity is the
      appropriate molecular function.
    action: MODIFY
    reason: >-
      Over-general parent; replace with GO:0047663.
    proposed_replacement_terms:
    - id: GO:0047663
      label: aminoglycoside 6'-N-acetyltransferase activity
- term:
    id: GO:0046677
    label: response to antibiotic
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: >-
      AAC(6')-Ib8 confers aminoglycoside resistance by acetylating (inactivating) the drug; 'response
      to antibiotic' is the appropriate biological process for a resistance enzyme.
    action: ACCEPT
    reason: >-
      Standard, well-supported BP for an antibiotic-modifying resistance enzyme; consistent with the
      CARD 'antibiotic inactivation' mechanism for ARO:3002579.
    supported_by:
    - reference_id: PMID:18710261
      supporting_text: "Enzymatic modification of aminoglycoside antibiotics mediated by regioselective aminoglycoside N-acetyltransferases is the predominant cause of bacterial resistance to aminoglycosides."
- term:
    id: GO:0047663
    label: aminoglycoside 6'-N-acetyltransferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000003
  qualifier: enables
  review:
    summary: >-
      The specific, correct molecular function (EC 2.3.1.82): acetyl-CoA-dependent acetylation of the
      6'-amino group of aminoglycosides (e.g. kanamycin B -> N(6')-acetylkanamycin B). This is the core
      function and exactly matches the EC and CARD AAC(6')-Ib family assignment.
    action: ACCEPT
    reason: >-
      EC 2.3.1.82-derived specific MF, consistent with the UniProt catalytic-activity reaction
      (kanamycin B + acetyl-CoA = N(6')-acetylkanamycin B + CoA), the AAC(6')-Ib family (CARD
      ARO:3002579), and the InterPro N6_acetyl_AAC6 signature (IPR030971). Retain as the core function.
    supported_by:
    - reference_id: PMID:18710261
      supporting_text: "Observation of the direct, and optimally positioned, interaction between the 6'-NH"
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:18710261
  qualifier: located_in
  review:
    summary: >-
      AAC(6')-Ib is a soluble GCN5-related N-acetyltransferase (GNAT) that uses cytoplasmic acetyl-CoA;
      it was expressed and purified as a soluble enzyme and structurally characterized. The expected
      cellular location is the cytoplasm; GOA carried no location term.
    action: NEW
    reason: >-
      Soluble cytoplasmic acetyltransferase using the cytoplasmic cofactor acetyl-CoA; adding the
      cellular component makes the annotation set complete.
    supported_by:
    - reference_id: PMID:18710261
      supporting_text: "The three-dimensional structure of AAC(6')-Ib-wt was determined in various complexes with donor and acceptor ligands to resolutions greater than 2.2"
core_functions:
- description: >-
    AAC(6')-Ib8 is an aminoglycoside 6'-N-acetyltransferase: it transfers an acetyl group from
    acetyl-CoA to the 6'-amino group of 4,6-disubstituted aminoglycosides, inactivating the drug and
    conferring aminoglycoside resistance.
  molecular_function:
    id: GO:0047663
    label: aminoglycoside 6'-N-acetyltransferase activity
  directly_involved_in:
  - id: GO:0046677
    label: response to antibiotic
  locations:
  - id: GO:0005737
    label: cytoplasm
  substrates:
  - id: CHEBI:57288
    label: acetyl-CoA
  supported_by:
  - reference_id: PMID:18710261
    supporting_text: "Enzymatic modification of aminoglycoside antibiotics mediated by regioselective aminoglycoside N-acetyltransferases is the predominant cause of bacterial resistance to aminoglycosides."
# CURATION NOTE (ARO->GO mapping QA): the ARO->GO mapping (ARO:3000121 'aminoglycoside acetyltransferase
# (AAC)' -> GO:0034069 'aminoglycoside N-acetyltransferase activity') would propose GO:0034069 for this
# entry. It is intentionally NOT added: GO:0034069 is the is_a PARENT of the existing, more specific
# GO:0047663 and would be a redundant over-annotation. This is the subsumption case flagged in the
# project spot review (the gain report should suppress a candidate when a more specific descendant is
# already annotated).
suggested_questions:
- question: >-
    Does AAC(6')-Ib8 carry any of the substitutions (e.g. Trp102Arg/Asp179Tyr) that, in the AAC(6')-Ib-cr
    variant, extend activity to fluoroquinolones, or is it a 'classical' aminoglycoside-only enzyme?
suggested_experiments:
- description: >-
    Determine acetylation kinetics (kcat/Km) against a panel of 4,6-aminoglycosides (kanamycin,
    amikacin, tobramycin, netilmicin) with acetyl-CoA, and test ciprofloxacin to exclude AAC(6')-Ib-cr
    activity.