actinophryid extrusome

cellstructuremech:actinophryid_extrusome · Membrane organelle · Membrane bounded organelle · Proposed

A secretory granule beneath the cell or axopodial surface of actinophryid protists, containing amorphous electron-dense material released during prey capture. [DOI:10.1016/j.ejop.2007.11.001]

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
GP40-type adhesive glycoprotein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Adhesive glycoprotein cargo implicated in prey attachment and ingestion. `DOI:10.1078/1434-4610-00041` The abstract identifies extrusome-stored GP40 and reports prey adhesion to GP40-coated beads.
extrusome membrane	Lipid	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Bounds the granule and contributes membrane during prey enclosure. `DOI:10.1002/cm.970020103` Electron microscopy links extrusome fusion to provision of food-vacuole membrane.

Taxonomic distribution

NCBITaxon:238771 Actinophrys sol — COMMON: Numerous extrusomes occur beneath the axopodial surface in studied cultures; this row does not assert presence in every strain or all actinophryids. [DOI:10.1007/BF01279469]

Canonical examples

NCBITaxon:238771 Actinophrys sol — Predatory protist used for extrusome cargo isolation and GP40-coated bead assays. [DOI:10.1078/1434-4610-00041]

Functions

prey adhesion — Extrusome contents contribute adhesive material during prey capture.
- DOI:10.1007/BF01279469 Isolated extrusome preparations adhered strongly to prey flagellates.
- DOI:10.1078/1434-4610-00041 Purified GP40 supported bead adhesion and induced ingestion of coated beads.
membrane supply during prey enclosure — Extrusome fusion supplies membrane while a feeding pseudopodium encloses prey.
- DOI:10.1002/cm.970020103

Mechanism graphs

Extrusome fusion supplies membrane during prey enclosure (FUNCTION)

Ultrastructural membrane-donation mechanism in Actinophrys sol.

Subject	Predicate	Object	Evidence
extrusome membrane	bounds	actinophryid extrusome	`DOI:10.1002/cm.970020103`
actinophryid extrusome	undergoes	extrusome fusion	`DOI:10.1002/cm.970020103`
extrusome fusion	supplies	prey food-vacuole membrane	`DOI:10.1002/cm.970020103`
prey food-vacuole membrane	contributes_to	prey enclosure	`DOI:10.1002/cm.970020103`
funnel-shaped feeding pseudopodium	mediates	prey enclosure	`DOI:10.1002/cm.970020103`

Discussions

CURATION_TODO (OPEN): Resolve an exact GP40 protein-family grounding and isoform-specific extrusome localization. B2NIF0 and B2NIF1 correspond to gp40-1 and gp40-2 direct submissions, not isoform-specific localization experiments in the 2001 study. Do not infer enzymatic activity from broad glucanase-related domains or add both sequences as experimentally localized protein examples.
CURATION_TODO (OPEN): Identify the lipid constituents of the extrusome membrane. Membrane continuity is evidenced, but lipid chemistry remains uncharacterized in the cited study.
INTERPRETATION (RESOLVED): Do not treat pharmacological targets as localized granule components. Channel-blocker and calmodulin-antagonist effects do not identify granule-resident proteins. Ionophore-mediated granule depletion was proposed but unverified, and Con A could target other surface glycoconjugates.
INTERPRETATION (RESOLVED): Keep actinophryid extrusomes distinct from ciliate extrusomes and context-specific vacuole terms. The source distinguishes amorphous actinophryid contents from organized ciliate extrusomes; toxicyst is not adopted as an exact synonym. GO:0043231 is the broader parent; GO:0030141 additionally assumes Golgi origin, not established here. The prey-vacuole membrane node remains ungrounded because GO:0020020 denotes a parasite vacuole digesting host cytoplasm.

Evidence

DOI:10.1016/j.ejop.2007.11.001 Kakuta and Suzaki (2008): accepted manuscript read via Kobe University; granule morphology and prey-capture pharmacology.
DOI:10.1007/BF01279469 Sakaguchi, Hausmann and Suzaki (1998): publisher summary read; isolated extrusome adhesion experiments.
DOI:10.1078/1434-4610-00041 Sakaguchi, Murakami and Suzaki (2001): PubMed abstract read; GP40 isolation and functional bead assays.
DOI:10.1002/cm.970020103 Hausmann and Patterson (1982): publisher-supplied abstract read via Crossref; electron-microscopic membrane-donation observations.

Curation history

2026-10-03T11:16:42Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-03T11:18:13Z codex · EXPANDED_RECORD — Added sourced GP40 cargo and membrane, species-scoped examples, adhesion and membrane-supply functions, a physical fusion mechanism, and explicit grounding and pharmacology limits.

Source: data/structures/membrane_organelle/actinophryid_extrusome.yaml