bilobe structure

GO:0120120 · Cytoskeleton · Other · Proposed

A cytoskeletal structure in some kinetoplastid species linking the structures of the ciliary pocket collar and the flagellum attachment zone. [GO:0120120]

Synonyms: kinetoplastid flagellar hook complex

Part of: GO:0005856 — cytoskeleton (no local record)

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
bilobe MORN-repeat protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	TbMORN1		UNKNOWN	A MORN-repeat bilobe protein that marks the hooked flagellar-pocket collar region and one arm of the bilobe hairpin. `DOI:10.1016/j.molbiopara.2009.05.001` Morriswood et al. 2009 identified TbMORN1 as a MORN-repeat protein present at the Trypanosoma brucei bilobe. `DOI:10.1128/EC.05287-11` Esson et al. 2012 localized TbMORN1 stably to the bilobe and resolved TbMORN1 along the hairpin arm nearest the microtubule quartet plus the hooked region above the flagellar pocket collar.
bilobe centrin proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	TbCentrin2, TbCentrin4		UNKNOWN	Centrin-family proteins that mark the bilobe and help delineate the hairpin arm nearest the flagellum attachment zone filament. `DOI:10.1128/EC.05287-11` Esson et al. 2012 localized TbCentrin2 and TbCentrin4 stably to the bilobe and resolved TbCentrin4 along the bilobe hairpin arm nearest the FAZ filament.

Taxonomic distribution

NCBITaxon:5691 Trypanosoma brucei — COMMON: The bilobe has been resolved cytologically in T. brucei as a hooked and hairpin-shaped cytoskeletal structure near the flagellar pocket collar, microtubule quartet and flagellum attachment zone filament. [DOI:10.1128/EC.05287-11]

Canonical examples

NCBITaxon:5691 Trypanosoma brucei — Trypanosome model in which TbMORN1, TbCentrin2, TbCentrin4 and TbLRRP1 localized to the bilobe, with TbMORN1 and TbCentrin4 delineating the hooked and hairpin regions around the pocket-collar and FAZ-associated cytoskeleton. [DOI:10.1128/EC.05287-11]

Functions

flagellar-pocket and FAZ cytoskeletal linkage — The bilobe is positioned between the flagellar pocket collar and the flagellum attachment zone and is arranged around the microtubule quartet plus FAZ filament.
- GO:0120120 GO defines the bilobe as a cytoskeletal structure in some kinetoplastids linking the ciliary pocket collar and flagellum attachment zone.
- DOI:10.1128/EC.05287-11 Esson et al. 2012 resolved the TbMORN1/TbCentrin4 bilobe hairpin around the microtubule quartet and FAZ filament, and placed the hooked TbMORN1 arm above the BILBO1-marked flagellar pocket collar.
- DOI:10.3390/cells4040726 Morriswood 2015 reviewed the bilobe as a flagellum-associated cytoskeletal structure of kinetoplastids.

Mechanism graphs

Bilobe protein cohorts flank pocket-associated cytoskeleton (FUNCTION)

TbMORN1 and bilobe centrins mark the hooked and hairpin regions of the T. brucei bilobe, which sits between the flagellar pocket collar and the flagellum attachment zone-associated microtubule quartet.

Subject	Predicate	Object	Evidence
bilobe MORN-repeat protein	localizes to	bilobe structure	`DOI:10.1016/j.molbiopara.2009.05.001` Morriswood et al. 2009 identified TbMORN1 at the bilobe rather than the basal bodies. `DOI:10.1128/EC.05287-11` Esson et al. 2012 mapped TbMORN1 onto the hooked region and one arm of the bilobe hairpin.
bilobe centrin proteins	localize to	bilobe structure	`DOI:10.1128/EC.05287-11` Esson et al. 2012 localized TbCentrin2 and TbCentrin4 stably to the T. brucei bilobe.
hooked bilobe region	sits above	ciliary pocket collar	`DOI:10.1128/EC.05287-11` Esson et al. 2012 localized the hooked TbMORN1 region above the BILBO1-marked FPC.
bilobe structure	flanks	microtubule quartet	`DOI:10.1128/EC.05287-11` Esson et al. 2012 placed the TbMORN1 and TbCentrin4 hairpin arms on either side of the microtubule quartet.
bilobe structure	aligns with	FAZ filament	`DOI:10.1128/EC.05287-11` Esson et al. 2012 resolved the TbCentrin4-positive hairpin arm alongside the FAZ filament.
bilobe structure	links	flagellum attachment zone	`GO:0120120` The GO:0120120 definition states the collar-to-FAZ linkage role used for this nonmechanistic edge.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral families for the bilobe-localized TbLRRP1 and broader MORN-repeat/centrin protein cohorts before expanding this record to additional hook-complex components. TbMORN1, TbLRRP1, TbCentrin2 and TbCentrin4 localize stably to the bilobe in T. brucei, but this first record only curates the MORN-repeat and centrin cohorts for which the verified evidence supports a morphological role.

Evidence

DOI:10.1016/j.molbiopara.2009.05.001 Morriswood et al. 2009, The bilobe structure of Trypanosoma brucei contains a MORN-repeat protein, Molecular and Biochemical Parasitology.
DOI:10.1128/EC.05287-11 Esson et al. 2012, Morphology of the trypanosome bilobe, a novel cytoskeletal structure, Eukaryotic Cell.
DOI:10.3390/cells4040726 Morriswood 2015, Form, Fabric, and Function of a Flagellum-Associated Cytoskeletal Structure, Cells.

Curation history

2026-09-12T10:53:08Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-12T10:54:53Z codex · EXPANDED_RECORD — Added GO synonymy and cytoskeleton parentage; curated MORN-repeat and centrin bilobe protein cohorts; added T. brucei taxonomic scope, a flagellar-pocket/FAZ linkage function, core literature evidence, a nonmechanistic bilobe positioning graph, and a TODO for exact bilobe protein-family groundings.
2026-09-12T11:01:24Z codex · ADDRESS_REVIEW — Resolved #634 by narrowing the ciliary-pocket-collar graph edge to the hooked TbMORN1-positive bilobe region; resolved #635 by removing broad Morriswood 2015 review support from the centrin component evidence.
2026-10-11T23:33:43Z codex · ADDRESS_SAVED_REVIEW — Addressed #2265: corrected cytoskeleton parthood without changing bilobe identity or historical morphology.

Source: data/structures/cytoskeleton/bilobe_structure.yaml