A0A515MEN7 · ACTPB_ACTFR

Function

function

Pore-forming toxin (PFT) that consists of a crown-shaped octamer or nonamer that forms cation-selective hydrophilic pores of about 1.5 nm (inside) and 13 nm (outside) and causes cytolysis (By similarity).
It causes cardiac stimulation (By similarity).
Also causes hemolysis (HC50=0.3 nM) (PubMed:31295915).
Interestingly, the Phe-16 is crucial for hemolysis (By similarity).
Pore formation is a multi-step process that involves specific recognition of membrane sphingomyelin (but neither cholesterol nor phosphatidylcholine) using aromatic rich region and adjacent phosphocholine (POC) binding site, firm binding to the membrane (mainly driven by hydrophobic interactions) accompanied by the transfer of the N-terminal region to the lipid-water interface and finally pore formation after oligomerization of monomers (By similarity).
It is probable that a dimeric form is an assembly intermediate before the complete oligomerization (By similarity).
The formation of stable pores occurs only in vesicles composed of DOPC/SM (there is no oligomerization when the PFT is treated with vesicles of DOPC or SM alone) (By similarity).
The transmembrane pore displays 8 lateral perforations, one at each subunit-subunit interface, partially occupied by the acyl-chain region of a bridging lipid (By similarity).
Each pore contains 24 lipid molecules, firmly bound to each subunit, that is, 3 lipids (L1, L2, L3, L4 and/or L5) are associated to each subunit (By similarity).
Lipid L1 bridges 2 subunits, whereas lipids L2 and L3 bind to sites at single subunit (By similarity).

Miscellaneous

This protein has been found to bind carbohydrates, since it shows a substantial delay in elution profile in size-exclusion chromatography. The carbohydrate pocket ovelaps with the lipid-binding module of actinoporins.

Temperature Dependence

Stable up to about 62 degrees Celsius.

Features

Showing features for site, binding site.

TypeIDPosition(s)Description
Site16Part of the hydrophobic cavity (in subunit A) that receives Val-60 from the adjacent subunit (B); essential in hemolysis, since it is critical for pore formation in cholesterol-rich membrane cells (such as red blood cells)
Binding site31an N-(acyl)-sphingosylphosphocholine 1 (UniProtKB | ChEBI); bridging lipid L1; in subunit A; in oligomeric forms only
Binding site51N-acetyl-D-glucosamine 6-sulfate (UniProtKB | ChEBI)
Binding site53an N-(acyl)-sphingosylphosphocholine 2 (UniProtKB | ChEBI); lipid L2; in monomeric and oligomeric forms
Binding site53N-acetyl-D-glucosamine 6-sulfate (UniProtKB | ChEBI)
Binding site54an N-(acyl)-sphingosylphosphocholine 2 (UniProtKB | ChEBI); lipid L2; in monomeric and oligomeric forms
Binding site79an N-(acyl)-sphingosylphosphocholine 1 (UniProtKB | ChEBI); bridging lipid L1; in subunit B; in oligomeric forms only
Binding site85an N-(acyl)-sphingosylphosphocholine 2 (UniProtKB | ChEBI); lipid L2; in monomeric and oligomeric forms
Binding site113an N-(acyl)-sphingosylphosphocholine 2 (UniProtKB | ChEBI); lipid L2; in monomeric and oligomeric forms
Binding site114an N-(acyl)-sphingosylphosphocholine 5 (UniProtKB | ChEBI); lipid L5; in monomeric and oligomeric forms
Binding site116an N-(acyl)-sphingosylphosphocholine 3 (UniProtKB | ChEBI); lipid L3; in monomeric and oligomeric forms
Binding site133an N-(acyl)-sphingosylphosphocholine 4 (UniProtKB | ChEBI); lipid L4; in monomeric and oligomeric forms
Binding site137an N-(acyl)-sphingosylphosphocholine 3 (UniProtKB | ChEBI); lipid L3; in monomeric and oligomeric forms
Binding site138an N-(acyl)-sphingosylphosphocholine 4 (UniProtKB | ChEBI); lipid L4; in monomeric and oligomeric forms
Binding site138N-acetyl-D-glucosamine 6-sulfate (UniProtKB | ChEBI)
Binding site144an N-(acyl)-sphingosylphosphocholine 5 (UniProtKB | ChEBI); lipid L5; in monomeric and oligomeric forms
Site149Part of the hydrophobic cavity (in subunit A) that receives Val-60 from the adjacent subunit (B)
Site163Part of the hydrophobic cavity (in subunit A) that receives Val-60 from the adjacent subunit (B)
Binding site168an N-(acyl)-sphingosylphosphocholine 1 (UniProtKB | ChEBI); bridging lipid L1; in subunit A; in oligomeric forms only

GO annotations

AspectTerm
Cellular Componentextracellular region
Cellular Componentnematocyst
Cellular Componentother organism cell membrane
Cellular Componentpore complex
Molecular Functionchannel activity
Molecular Functionlipid binding
Molecular Functiontoxin activity
Biological Processcytolysis in another organism
Biological Processmonoatomic cation transport
Biological Processpore complex assembly

Keywords

Names & Taxonomy

Protein names

  • Recommended name
    DELTA-actitoxin-Afr1c
  • Short names
    DELTA-AITX-Afr1c
  • Alternative names
    • Alpha-helical pore-forming toxin
      (PFT
      )
    • Cytolysin
    • Fragaceatoxin B
      (fraB
      )

Organism names

Accessions

  • Primary accession
    A0A515MEN7

Subcellular Location

Secreted
Nematocyst
Target cell membrane
Note: Forms an alpha-helical membrane channel in the prey.

Keywords

PTM/Processing

Features

Showing features for chain.

TypeIDPosition(s)Description
ChainPRO_00004538231-179DELTA-actitoxin-Afr1c

Interaction

Subunit

Octamer or nonamer in membranes. Monomer in the soluble state.

Family & Domains

Features

Showing features for region, motif.

TypeIDPosition(s)Description
Region1-29N-terminal alpha-helix that contributes to the pore
Region11-30N-terminal region
Region105-120Trp-rich region, which is important for the binding to lipid membrane
Motif144-146Cell attachment site, crucial for protein stability

Domain

Composed of a long N-terminal alpha-helix and a core region rich in beta-sheet structures. Before the pore formation, the alpha-helix binds the lipid membrane, partitions into the lipid-water interface and stabilizes the monomeric molecule on the membrane. Finally, it traverses the bilayer, thus forming the transmembrane pore.

Sequence similarities

Keywords

Family and domain databases

Sequence

  • Sequence status
    Complete
  • Length
    179
  • Mass (Da)
    19,672
  • Last updated
    2021-09-29 v2
  • Checksum
    BA2341AA9D3E5FF5
SAEVAGAIIDGASLTFDVLQTVLKALGDVSRKIAVGIDNEPGMTWTAMNTYFRSGTSDVILPHTVPHSKALLYDGQKNRGPVTTGVVGVIAYAMSDGNTLAVLFSIPFDYNLYSNWWNVKVYKGHRRADQAMYEELYYDFSPFRGDNGWHTKSIGYGLKGRGFMNSSGKAILQIHVNKV

Mass Spectrometry

Molecular mass is 19,672 Da. Determined by Electrospray.

Keywords

Sequence databases

Nucleotide SequenceProtein SequenceMolecule TypeStatus
MK936900
EMBL· GenBank· DDBJ
QDM54907.1
EMBL· GenBank· DDBJ
mRNA

Similar Proteins

Disclaimer

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