trichocyst

GO:0055039 · Membrane organelle · Membrane bounded organelle · Proposed

A crystalline exocytotic organelle composed of small, acidic proteins existing primarily as disulphide-linked dimers. The trichocyst releases long filamentous proteins that capture predators in net-like structures to slow them down when the cell is disturbed. [GO:0055039]

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
trichocyst matrix proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)				Small acidic secretory proteins that coassemble into the crystalline matrix of the Paramecium trichocyst body. `DOI:10.1091/mbc.6.6.649` Madeddu et al. 1995 cloned a Paramecium multigene family encoding polypeptides of the crystalline trichocyst matrix. `DOI:10.1111/jeu.12332` Plattner 2017 reviewed Paramecium trichocyst bodies as crystalline matrices assembled from Trichocyst Matrix Proteins.

Taxonomic distribution

NCBITaxon:5888 Paramecium tetraurelia — COMMON: Dense-core trichocysts and their crystalline matrix proteins have been characterized in Paramecium tetraurelia. [DOI:10.1091/mbc.6.6.649]

Canonical examples

NCBITaxon:5888 Paramecium tetraurelia — Ciliate model in which a multigene family encoding the crystalline trichocyst matrix proteins was identified. [DOI:10.1091/mbc.6.6.649]

Functions

stimulus-triggered filament discharge — Trichocysts undergo regulated exocytosis, contact extracellular Ca2+, and recrystallize a condensed matrix as an elongated extracellular filament.
- DOI:10.1111/jeu.12332 Plattner 2017 reviewed Paramecium trichocysts as projectile-like secretory organelles that discharge in a stimulus-triggered reaction.

Mechanism graphs

Calcium-triggered matrix proteins discharge as a filament (FUNCTION)

Paramecium trichocyst matrix proteins coassemble into a crystalline trichocyst matrix that is stored in the organelle. After stimulated exocytosis, extracellular Ca2+ triggers matrix recrystallization and extension into the discharged filament.

Subject	Predicate	Object	Evidence
trichocyst matrix proteins	coassemble into	crystalline trichocyst matrix	`DOI:10.1091/mbc.6.6.649` Madeddu et al. 1995 identified the TMP multigene family encoding crystalline trichocyst matrix polypeptides in Paramecium.
crystalline trichocyst matrix	is stored in	trichocyst	`DOI:10.1111/jeu.12332` Plattner 2017 reviewed Paramecium trichocyst bodies as condensed crystalline secretory matrices.
calcium(2+)	triggers recrystallization of	crystalline trichocyst matrix	`DOI:10.1111/jeu.12332` Plattner 2017 reviewed extracellular Ca2+-triggered matrix recrystallization as the transition that powers Paramecium trichocyst projection.
crystalline trichocyst matrix	recrystallizes into	extended trichocyst filament	`DOI:10.1111/jeu.12332` Plattner 2017 described the rapid extracellular-Ca2+-driven discharge of condensed Paramecium trichocysts into extended projectile-like structures.

Discussions

CURATION_TODO (OPEN): Resolve exact family groundings and boundaries for trichocyst matrix, membrane and tip components. This first record includes the experimentally cloned crystalline matrix protein family. Additional tip, sheath and membrane constituents should be added only after exact family groundings and their relationship to the mature, discharge-competent trichocyst are resolved.

Evidence

GO:0055039 Gene Ontology cellular-component term for trichocyst.
DOI:10.1091/mbc.6.6.649 Madeddu et al. 1995, A large multigene family codes for the polypeptides of the crystalline trichocyst matrix in Paramecium, Molecular Biology of the Cell.
DOI:10.1111/jeu.12332 Plattner 2017, Trichocysts-Paramecium's Projectile-like Secretory Organelles, Journal of Eukaryotic Microbiology.

Curation history

2026-09-10T11:12:03Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-10T11:12:57Z claude · EXPANDED_RECORD — Added Paramecium trichocyst matrix proteins as a reviewed-label-only constituent, Paramecium tetraurelia taxonomic scope and canonical example, a stimulus-triggered discharge function, record-level trichocyst evidence, a matrix discharge graph and a grounding TODO for matrix, membrane and tip components.
2026-09-10T11:20:58Z claude · ADDRESS_REVIEW — Addressed PR #353 review issues #354 and #355 by adding extracellular Ca2+-triggered trichocyst matrix recrystallization to the discharge graph and removing the uncoupled Pease 1947 record-level citation.

Source: data/structures/membrane_organelle/trichocyst.yaml