archaeal-type flagellum

GO:0097589 · Appendage · Appendage · Proposed

A non-membrane-bounded motility organelle, also called the archaellum, characterized in Archaea and in the bacterium Litorilinea aerophila; a membrane-associated motor drives swimming through rotation of extracellular type-IV-pilin-like archaellin filaments. [DOI:10.1038/s41564-025-02110-8]

Synonyms: archaellum; archaeal flagellum

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
archaellin filament subunits	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	arlA, arlB, flaA, flaB	ESSENTIAL	Glycosylated type-IV-pilin-like subunits that polymerize into the extracellular helical filament. `DOI:10.3389/fmicb.2015.00023` Albers and Jarrell 2015 review prearchaellin processing, N-glycosylation and filament assembly from archaellin subunits. `DOI:10.1038/s41467-022-28337-1` Gambelli et al. 2022 solved the Methanocaldococcus villosus archaellum filament and found two alternating archaellins, ArlB1 and ArlB2, in the filament.
ArlI/ArlJ archaellum motor core	Protein complex	part of	Reviewed label only (reviewed name; no accession asserted)	arlI, arlJ, flaI, flaJ	ESSENTIAL	Cytosolic AAA+ ATPase and polytopic membrane platform that assemble and rotate the archaellum filament by ATP hydrolysis. `DOI:10.3389/fmicb.2015.00023` Albers and Jarrell 2015 review FlaI/ArlI as the assembly ATPase and FlaJ/ArlJ as the only polytopic membrane protein conserved in archaellum operons.
ArlH motor regulator	Protein	part of		arlH, flaH	ESSENTIAL	Nucleotide-dependent motor protein that interacts with ArlI/FlaI and is required for archaellum assembly and function in the studied motor. `DOI:10.1111/mmi.13260` Chaudhury et al. 2016 tested the nucleotide-dependent FlaH-FlaI interaction and its requirement for archaellum motor assembly and function.
ArlF/ArlG S-layer anchor	Protein complex	part of		arlF, arlG, flaF, flaG	CONDITIONAL	Envelope-side FlaF/FlaG module proposed to anchor the archaellum to the S-layer in characterized archaeal lineages; binding and complex-formation experiments support the model without resolving every motor contact. `DOI:10.1016/j.str.2015.03.001` Banerjee et al. 2015 demonstrated binding of soluble Sulfolobus acidocaldarius FlaF to isolated S-layer and proposed an anchoring role; the complete FlaF/FlaG-to-motor bridge was not directly resolved. `DOI:10.1038/s41564-019-0622-3` The inspected Tsai et al. 2020 primary abstract reports FlaG/FlaF complex formation and motility-disrupting interface mutations, supporting an S-layer-anchoring model. Full text was unavailable; direct contacts to the intact motor are not established by this abstract.
ArlX/ArlCDE cytosolic scaffold	Protein complex	part of	Reviewed label only (reviewed name; no accession asserted)	arlX, arlC, arlD, arlE, flaX	CONDITIONAL	Lineage-specific cytosolic ring or switch module that organizes the motor ATPase and links the archaellum to chemotaxis control. `DOI:10.1074/jbc.M112.414383` Banerjee et al. 2012 showed that crenarchaeal FlaX forms ring-shaped assemblies and interacts with FlaI. `DOI:10.1038/s41467-022-28337-1` Gambelli et al. 2022 summarize ArlX in Crenarchaeota and ArlCDE in Euryarchaeota as cytosolic ring modules surrounding the motor. `DOI:10.1111/febs.12534` The inspected abstract of Banerjee et al. 2013 reports that Sulfolobus acidocaldarius FlaX interacts with FlaI and FlaH in the cytoplasmic archaellum complex. The full text was not accessible for this curation.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

ArlH motor regulator

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q4J9K9`	Archaeal flagellar ATP-binding protein FlaH	flaH	Sulfolobus acidocaldarius DSM 639 (`NCBITaxon:330779`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene flaH in Sulfolobus acidocaldarius DSM 639, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `PMID:24103130` Banerjee A et al. 2013, ‘Insights into subunit interactions in the Sulfolobus acidocaldarius archaellum cytoplasmic complex.’, FEBS J. ECO:0000269 experimental evidence cited by UniProt for the 'Archaeal flagellum' localisation of Q4J9K9.

Taxonomic distribution

NCBITaxon:2157 Archaea — VARIABLE: Archaella are archaeal motility organelles whose operons are patchily distributed across archaeal genomes. [DOI:10.3389/fmicb.2015.00023]
NCBITaxon:2 Bacteria — VARIABLE: Litorilinea aerophila DSM 25763 forms archaellin filaments and swims after growth on motility plates. Other Chloroflexota candidates are supported by genome surveys, not equivalent experimental observations. [DOI:10.1038/s41564-025-02110-8]

Canonical examples

NCBITaxon:2285 Sulfolobus acidocaldarius — Crenarchaeal model for biochemical characterization of FlaX ring formation and interaction with the motor ATPase FlaI, as reported in the inspected primary abstract. [DOI:10.1074/jbc.M112.414383]
NCBITaxon:2261 Pyrococcus furiosus — Euryarchaeal model for in situ cryo-ET of the archaellum machinery at the cell envelope. [DOI:10.7554/eLife.27470]
NCBITaxon:667126 Methanocaldococcus villosus — Source of a high-resolution heteropolymeric archaellum filament structure with alternating ArlB1 and ArlB2 subunits. [DOI:10.1038/s41467-022-28337-1]

Functions

archaeal-type flagellum-dependent cell motility GO:0097590 — Rotation of the archaellum filament drives swimming in characterized archaea and in Litorilinea aerophila.
- DOI:10.3389/fmicb.2015.00023 Albers and Jarrell 2015 review archaellum-driven archaeal swimming and the ATP-powered motor that distinguishes it from ion-powered bacterial flagella.
- DOI:10.1038/s41564-025-02110-8 The study links experimentally identified archaellum filaments to swimming in Litorilinea aerophila.

Mechanism graphs

ATP-driven basal assembly builds and rotates the archaellum filament (ASSEMBLY)

Prearchaellins are processed and assembled by an ATP-powered ArlI/ArlJ motor. ArlH and lineage-specific scaffold proteins organize that motor; envelope-side FlaF/FlaG proteins are proposed to anchor it to the S-layer. Motor-driven filament rotation propels archaeal cells.

Subject	Predicate	Object	Evidence
PibD/FlaK prepilin peptidase	matures	prearchaellins	`DOI:10.3389/fmicb.2015.00023` Albers and Jarrell 2015 review class-3 signal-peptide processing of prearchaellins by PibD or FlaK-like enzymes.
mature archaellins	polymerize into	archaeal-type flagellum	`DOI:10.1038/s41467-022-28337-1` Gambelli et al. 2022 resolved the Methanocaldococcus villosus filament as a polymer of alternating ArlB1 and ArlB2 archaellins.
ArlX/ArlCDE cytosolic scaffold	organizes	ArlI/ArlJ motor core	`DOI:10.1074/jbc.M112.414383` Banerjee et al. 2012 showed that FlaX forms oligomeric rings and interacts with FlaI in the Sulfolobus acidocaldarius motor. `DOI:10.1038/s41467-022-28337-1` Gambelli et al. 2022 summarize the Crenarchaeota versus Euryarchaeota ring modules surrounding ArlI/ArlJ.
ArlH motor regulator	regulates	ArlI/ArlJ motor core	`DOI:10.1111/mmi.13260` Chaudhury et al. 2016 established the nucleotide-dependent FlaH-FlaI interaction and its requirement for archaellum assembly and function.
ArlF/ArlG S-layer anchor	is proposed to anchor	ArlI/ArlJ motor core	`DOI:10.1016/j.str.2015.03.001` Banerjee et al. 2015 demonstrated binding of soluble Sulfolobus acidocaldarius FlaF to isolated S-layer and proposed an anchoring role; the complete FlaF/FlaG-to-motor bridge was not directly resolved. `DOI:10.1038/s41564-019-0622-3` The inspected Tsai et al. 2020 primary abstract reports FlaG/FlaF complex formation and motility-disrupting interface mutations, supporting an S-layer-anchoring model. Full text was unavailable; direct contacts to the intact motor are not established by this abstract.
ArlI/ArlJ motor core	assembles and rotates	archaeal-type flagellum	`DOI:10.3389/fmicb.2015.00023` Albers and Jarrell 2015 review FlaI/ArlI as the ATPase that powers archaeal flagellum assembly and rotation.
archaeal-type flagellum	drives	archaeal-type flagellum-dependent cell motility	`DOI:10.3389/fmicb.2015.00023` Albers and Jarrell 2015 review archaellum rotation as the archaeal swimming mechanism.

Discussions

CURATION_TODO (OPEN): Resolve exact family or complex CURIEs for archaellins, the ArlI/ArlJ motor core, ArlH, ArlF/ArlG and lineage-specific cytosolic scaffold proteins. The first archaellum record follows Arl/Fla nomenclature and leaves family grounding unset where adopting a broad type-IV-pilus or ATPase family would overmerge non-archaellum proteins.

Evidence

DOI:10.3389/fmicb.2015.00023 Albers SV and Jarrell KF 2015, The archaellum: how Archaea swim, Frontiers in Microbiology.
DOI:10.1074/jbc.M112.414383 Banerjee et al. 2012, FlaX, a unique component of the crenarchaeal archaellum, forms oligomeric ring-shaped structures and interacts with the motor ATPase FlaI, Journal of Biological Chemistry.
DOI:10.1016/j.str.2015.03.001 Banerjee et al. 2015, FlaF is a beta-sandwich protein that anchors the archaellum in the archaeal cell envelope by binding the S-layer protein, Structure.
DOI:10.1111/mmi.13260 Chaudhury et al. 2016, The nucleotide-dependent interaction of FlaH and FlaI is essential for assembly and function of the archaellum motor, Molecular Microbiology.
DOI:10.7554/eLife.27470 Daum et al. 2017, Structure and in situ organisation of the Pyrococcus furiosus archaellum machinery, eLife.
DOI:10.1038/s41467-022-28337-1 Gambelli et al. 2022, An archaellum filament composed of two alternating subunits, Nature Communications.
DOI:10.1038/s41564-025-02110-8 Sivabalasarma et al. 2025 experimentally identified archaellum filaments and swimming in Litorilinea aerophila; motor architecture was assessed with genomic and structural predictions.

Curation history

2026-09-04T16:17:00Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-04T16:17:39Z claude · EXPANDED_RECORD — Added archaeal-type flagellum synonyms, components, taxonomy, examples, function, literature evidence, a base-assembly graph, and a protein-family grounding todo.
2026-09-08T07:38:33Z uniprot_genes · SEED_PROTEIN_EXAMPLES — #183: added 1 protein example(s) by resolving each of the component's declared gene symbols to the single reviewed UniProtKB entry for that symbol in a taxon this record names, deduplicated by accession. Symbols resolving to more than one reviewed entry were skipped rather than chosen between.
2026-10-10T06:07:43Z claude · ADDRESS_REVIEW — Addressed issues #2112 and #2113: moved the 2013 FlaX/FlaI/FlaH interaction citation from the ArlI/ArlJ motor core to the cytosolic scaffold, with explicit abstract-only access, and narrowed the Sulfolobus canonical example to the cited 2012 FlaX/FlaI result. Preserved other biological claims and PROPOSED status.
2026-10-10T07:08:33Z claude · ADDRESS_REVIEW — Addressed #2115: replaced bacterial absence with bounded 2025 experimental and inferred evidence, retaining archaeal graph scope. Addressed #2117: distinguished FlaF binding data and the FlaG/FlaF anchoring model with claim-level, abstract-limited 2020 evidence. Preserved PROPOSED status.

Source: data/structures/appendage/archaeal_type_flagellum.yaml