nas-8 (Sc-AST) is a secreted zinc-dependent astacin metalloendopeptidase (EC 3.4.24.21; MEROPS family M12A) from the entomopathogenic nematode Steinernema carpocapsae. It is synthesized as a precursor comprising an N-terminal signal peptide and a propeptide (zymogen) that are removed to yield the mature, catalytically active protease, which contains a peptidase M12A (astacin) catalytic domain and a C-terminal ShK-toxin (ShKT) domain. Catalysis requires a single active-site zinc ion coordinated by the conserved HExxH motif and a downstream histidine, and a methionine-turn; activity is abolished by the metal chelators EDTA, EGTA and 1,10-phenanthroline. The mature enzyme hydrolyzes protein and peptide substrates (demonstrated against gelatin and azocasein), cleaving peptide bonds preferentially with Ala in the P1' position. The protein is secreted into the extracellular environment, is expressed in the infective and parasitic juvenile stages but not in eggs or adults, and is strongly induced by contact with insect host tissues, consistent with a role in degrading host proteins during invasion of the insect haemocoel and the parasitic process.
The preferred accession for this review is D2KBH9. These relationships are manually assessed.
REFERENCE PROTEOME EQUIVALENT · Reviewed 2026-10-19
Reference proteome: UP000298663
Retain D2KBH9 as the primary Swiss-Prot accession. The 418-residue reference protein differs by one residue across full ungapped coverage (99.76% identity), with a large separation from other metallopeptidase hits. This supports a qualified sequence-based counterpart assessment. The source protein is from strain Breton; the origin and biological effect of the single residue difference are not established.
MMseqs2 searched 35,146 sequences across UP000298663 at E <= 1e-5 and sensitivity 7.5, returning 44 hits. Every returned sequence was globally aligned using BLOSUM62 with gap-open -10 and extension -0.5. Scores and sequences for all 44 returned candidates are retained, with 10 detailed alignment files. The heuristic search does not establish genomic absence or unique locus identity.
file:STECR/nas-8/nas-8-record-evidence.yaml
target_sequence_count: 35146
file:STECR/nas-8/nas-8-record-evidence.yaml
candidate_count: 44
A0A4U8UYW6: 417 identities across 418 global-alignment columns (99.7608% identity including gaps), 1 substitutions and 0 gap columns. Query coverage is 100.0%; target coverage is 100.0%. Sequence similarity is interpreted in the manual rationale. Identity over paired residues is 99.7608% (417/418); gap columns are excluded from this denominator.
file:STECR/nas-8/nas-8-record-evidence.yaml
query_length: 418 target_length: 418 alignment_columns: 418 identities: 417 mismatches: 1 gap_columns: 0 identity_percent: 99.7608 query_coverage_percent: 100.0 target_coverage_percent: 100.0
The primary accession is outside every searched exact-taxon reference proteome. Current UniProt records place A0A4U8UYW6 in UP000298663 and give it the same taxon as the primary.
file:STECR/nas-8/nas-8-record-evidence.yaml
primary_in_any_reference_proteome: false
file:STECR/nas-8/nas-8-record-evidence.yaml
alternative_in_reference_proteome: true
file:STECR/nas-8/nas-8-record-evidence.yaml
same_taxon: true
Sampled UniSave observations: 09-DEC-2015, entry version 30.: no Proteomes cross-reference; 02-DEC-2020, entry version 51.: no Proteomes cross-reference; 27-NOV-2024, entry version 56.: no Proteomes cross-reference. These dated observations do not establish uninterrupted membership/absence, the exact change date, or UniProt's motivation.
file:STECR/nas-8/nas-8-record-evidence.yaml
entry_date: 09-DEC-2015, entry version 30. proteomes: []
file:STECR/nas-8/nas-8-record-evidence.yaml
entry_date: 02-DEC-2020, entry version 51. proteomes: []
file:STECR/nas-8/nas-8-record-evidence.yaml
entry_date: 27-NOV-2024, entry version 56. proteomes: []
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004222 metalloendopeptidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic annotation (from EC 3.4.24.21, InterPro M12A astacin domain and PANTHER) asserting metalloendopeptidase activity. This is the core molecular function of the protein and is independently supported by direct experimental characterization of the recombinant enzyme (PMID:20670659), which demonstrated zinc-dependent, chelator-inhibited endopeptidase activity against gelatin and azocasein. Accept and retain as a core function. |
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: Subcellular location mapping from UniProt (SL-0243, Secreted). The protein carries a cleaved N-terminal signal peptide and is described as a secreted protease that acts on host tissues during invasion, so localization to the extracellular region is well supported. Accept. |
| GO:0006508 proteolysis | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro2GO biological-process annotation for proteolysis. This correctly reflects the enzyme's activity (peptide-bond hydrolysis demonstrated against gelatin and azocasein) and is the direct biological-process consequence of its endopeptidase function. Accurate but generic; retained as a non-core process because the more informative statement of function is captured by the molecular-function term. |
| GO:0008237 metallopeptidase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: InterPro2GO annotation for metallopeptidase activity. This is correct but is a less specific parent of GO:0004222 (metalloendopeptidase activity), which is the experimentally supported and more informative term for this astacin endopeptidase. Marking as over-annotated in favor of the more specific child term that is already present. |
| GO:0008270 zinc ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO annotation for zinc ion binding. Consistent with the astacin mechanism: the active site coordinates one catalytic Zn(2+) ion via the conserved HExxHxxGxxH zinc-binding motif, and activity is abolished by metal chelators (EDTA, EGTA, o-phenanthroline; PMID:20670659). Accept as a supporting molecular function underpinning catalysis. |
| GO:0004222 metalloendopeptidase activity | EXP PMID:20670659 Cloning, characterisation and heterologous expression of an ... | ACCEPT | Summary: Experimental (EXP) annotation from PMID:20670659. Recombinant Sc-AST was purified and shown to hydrolyze gelatin and azocasein, with activity inhibited by the divalent-metal chelators EDTA, EGTA and o-phenanthroline, and kinetic parameters (Km, Vmax, kcat) determined. This directly establishes zinc-dependent metalloendopeptidase activity and is the core function of the gene. Accept and retain as core. |
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