id: D5SHU8
gene_symbol: ttv
taxon:
  id: NCBITaxon:7227
  label: Drosophila melanogaster
status: COMPLETE
description: The native short Ttv isoform retains a conserved C-terminal GT64 glycosyltransferase domain,
  but its autonomous activity and physiological access to substrates are unverified.
source_documents:
- genes/DROME/ttv/ttv-protnlm-source.json
- genes/DROME/ttv/ttv-bioinformatics/RESULTS.md
- genes/DROME/ttv/ttv-flybase.txt
- genes/DROME/ttv/ttv-hypotheses/fly41-short-isoform-glycosyltransferase/openscientist.md
predictions:
- source_method: ProtNLM2
  source_version: UniProt API snapshot 2026-09-08
  source_reference_id: file:DROME/ttv/ttv-protnlm-source.json
  predicted_term:
    id: GO:0016757
    label: glycosyltransferase activity
  predicted_term_type: GO_MF
  review:
    assessment: UNC
    confidence_score: 1
    summary: D5SHU8 is the 299-residue ttv-PC isoform, not the full-length 760-residue protein. The
      retained C-terminal region contains the annotated catalytic Asp and multiple ligand-binding residues, so
      short length does not justify categorical refutation of glycosyltransferase activity. However, the
      other domain and N-terminal targeting/anchor region are absent, and the current data do not establish
      folding, complex support or substrate access in PC. An equivalent electronic annotation exists but
      adds no independent validation. OpenScientist found the broad parent term defensible by homology
      but still cautioned that catalytic evidence is from full-length Ttv, not isolated D5SHU8. Target-specific
      activity or a convincing domain-level functional analysis is missing; UNC preserves this distinction.
    supported_by:
    - reference_id: file:DROME/ttv/ttv-bioinformatics/RESULTS.md
      supporting_text: The C-terminal glycosyltransferase-region active-site Asp670 maps to target Asp209,
        and the source-record nucleotide-sugar/metal-binding residues in this region are retained.
    - reference_id: file:DROME/ttv/ttv-flybase.txt
      supporting_text: ttv-PC FBpp0305368 34.4 299 9.71 D5SHU8 NP_001260972 AGB93504
    - reference_id: PMID:36593275
      supporting_text: 'EXT1 and EXT2, where each protein monomer contains distinct GT47 (GT-B fold) and

        GT64 (GT-A fold) glycosyltransferase domains.'
    - reference_id: file:DROME/ttv/ttv-hypotheses/fly41-short-isoform-glycosyltransferase/openscientist.md
      supporting_text: Of the nine canonical catalytic/substrate-binding residues, **8 are retained**
        in D5SHU8, including the active-site **Asp670 → Asp209** and the **DED binding motif (canonical
        581–583 → D5SHU8 120–122)**
references:
- id: file:DROME/ttv/ttv-bioinformatics/RESULTS.md
  title: RESULTS.md
  findings: []
- id: file:DROME/ttv/ttv-flybase.txt
  title: ttv-flybase.txt
  findings: []
- id: PMID:36593275
  title: Structural basis for heparan sulfate co-polymerase action by the EXT1-2 complex.
  findings: []
- id: file:DROME/ttv/ttv-hypotheses/fly41-short-isoform-glycosyltransferase/openscientist.md
  title: OpenScientist audit of the Ttv short-isoform glycosyltransferase prediction
  findings:
  - statement: OpenScientist confirmed that D5SHU8 is the isolated C-terminal GT64 domain of Ttv and
      preserves most catalytic machinery.
    supporting_text: The 299-residue D5SHU8 sequence aligns **co-linearly and with 100% identity (299/299)
      to residues 462–760 of the canonical reviewed ttv protein Q9V730 (760 aa)**, beginning at canonical
      offset 461.
  - statement: OpenScientist found direct catalytic evidence for full-length Ttv/EXT1 rather than for
      the isolated D5SHU8 isoform.
    supporting_text: No published study reports catalytic activity for an isolated EXT1/ttv GT64 domain,
      nor for this specific 299-aa isoform.