flagella connector

GO:0120118 · Appendage · Other · Proposed

A mobile transmembrane junction at the tip of the flagellum of some kinetoplastid species linking the tip of a new growing flagellum to an older flagellum. [GO:0120118]

Synonyms: FC

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

Taxonomic distribution

• NCBITaxon:5691 Trypanosoma brucei — VARIABLE: The flagella connector is a division-stage junction in procyclic Trypanosoma brucei that links the tip of the new flagellum to the old flagellum. [DOI:10.1242/jcs.00995]

Canonical examples

• NCBITaxon:5691 Trypanosoma brucei — African trypanosome model in which the flagella connector was defined as a motile transmembrane junction and later resolved by electron and cryo-electron tomography. [DOI:10.1371/journal.pntd.0004312]

Functions

• new-to-old flagellum linkage — The FC couples the distal tip of the growing new flagellum to the flank of the old flagellum during T. brucei flagellum biogenesis.
  • DOI:10.1242/jcs.00995 Briggs et al. 2004 characterized the T. brucei flagella connector as a mobile transmembrane junction linking the new and old flagella.
  • DOI:10.1371/journal.pntd.0004312 Hoog et al. 2016 resolved FC layers between the new and old flagella by electron tomography and cryo-electron tomography.
• new-flagellum tip tracking — The FC remains associated with the tip of the assembling new flagellum while moving along the old flagellum.
  • DOI:10.1126/science.1063775 Moreira-Leite et al. 2001 first described the motile junction that connects the growing new flagellum to the old flagellum during trypanosome cell division.
  • DOI:10.1242/jcs.03203 Davidge et al. 2006 used intraflagellar-transport mutants to dissect FC movement from extension of the new flagellar axoneme.
• new-tip to old-shaft microtubule coupling — FC-associated proteins link the connector membrane junction to extending microtubule tips in the assembling new flagellum and to axonemal microtubules along the lateral shaft of the mature old flagellum.
  • DOI:10.1073/pnas.1703553114 Varga et al. 2017 assigned a kinesin-15 family member to the link with extending new-flagellum microtubule tips and a kinetoplastid-specific kinesin to attachment to mature-flagellum microtubules. This does not place the old-side attachment at the old distal tip or equate the connector with the separate axonemal cap.
  • DOI:10.1371/journal.pntd.0004312 Hoog et al. 2016 resolved the connector between the new flagellum tip and the lateral side of the old flagellum; it travels along the old flagellum and stops roughly halfway along its length. This supplies the spatial context for the mature-flagellum microtubule attachment.

Discussions

• CURATION_TODO (OPEN): Resolve the complete set of T. brucei FC constituent proteins and their exact source-neutral groundings. Varga et al. 2017 identified seven flagella-connector constituents and three axonemal-capping-structure constituents. This first record defers component curation until the connector, axonemal cap and adjacent distal-tip boundaries can be separated without absorbing neighboring structures.
• CURATION_TODO (OPEN): Model the FC motor and old- versus new-flagellum attachment mechanisms once the kinesin components have exact boundaries. Davidge et al. 2006 showed that FC motility is separable from new-axoneme extension, and Varga et al. 2017 assigned kinesin-family proteins to opposite FC attachment sides. The motility graph should wait until those proteins are curated as FC components or deliberately excluded.

Evidence

• DOI:10.1126/science.1063775 Moreira-Leite, Sherwin, Kohl and Gull 2001, A trypanosome structure involved in transmitting cytoplasmic information during cell division, Science.
• DOI:10.1242/jcs.00995 Briggs et al. 2004, The flagella connector of Trypanosoma brucei: an unusual mobile transmembrane junction, Journal of Cell Science.
• DOI:10.1242/jcs.03203 Davidge et al. 2006, Trypanosome IFT mutants provide insight into the motor location for mobility of the flagella connector and flagellar membrane formation, Journal of Cell Science.
• DOI:10.1371/journal.pntd.0004312 Hoog et al. 2016, 3D Architecture of the Trypanosoma brucei Flagella Connector, a Mobile Transmembrane Junction, PLOS Neglected Tropical Diseases.
• DOI:10.1073/pnas.1703553114 Varga, Moreira-Leite, Portman and Gull 2017, Protein diversity in discrete structures at the distal tip of the trypanosome flagellum, Proceedings of the National Academy of Sciences of the United States of America.

Curation history

• 2026-10-03T03:49:04Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
• 2026-10-03T03:51:37Z codex · EXPANDED_RECORD — Added FC synonymy and cell-junction parentage, Trypanosoma brucei taxonomic scope, new-to-old flagellar-tip coupling functions, core literature evidence, and open component-boundary discussions.
• 2026-10-11T02:44:54Z claude · ADDRESS_SAVED_REVIEW — Addressed #2166: corrected connector coupling from distal tips on both flagella to new-tip versus old-shaft attachment, with scoped Varga protein evidence and independent Hoog spatial evidence. Preserved stable function ID, open molecular inventory and PROPOSED status.

Source: data/structures/appendage/flagella_connector.yaml