archaeal-type flagellum filament

cellstructuremech:archaeal_type_flagellum_filament · Appendage · Filament · Proposed

An extracellular helical archaellum filament assembled from glycosylated type-IV-pilin-like archaellin subunits and rotated by the archaeal-type flagellum motor for swimming; characterized in Archaea and in the bacterium Litorilinea aerophila. [DOI:10.1038/s41564-025-02110-8]

Synonyms: archaellum filament

Part of: archaeal-type flagellum (GO:0097589)

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
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 of the archaeal-type flagellum. `DOI:10.3389/fmicb.2015.00023` Albers and Jarrell 2015 review archaellin maturation, N-glycosylation, and assembly into the rotating archaellum filament. `DOI:10.1038/s41467-022-28337-1` Gambelli et al. 2022 resolved the Methanocaldococcus villosus archaellum filament as a polymer of alternating ArlB1 and ArlB2 archaellins.

Taxonomic distribution

NCBITaxon:2157 Archaea — VARIABLE: Archaellum filaments occur in archaeal lineages that encode the archaeal-type flagellum; archaellum operons are patchily distributed across Archaea. [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:667126 Methanocaldococcus villosus — Source archaeon for a high-resolution heteropolymeric archaellum filament structure built from 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 rotation as the archaeal swimming mechanism.
- DOI:10.1038/s41564-025-02110-8 The study links experimentally identified archaellum filaments to swimming in Litorilinea aerophila.

Mechanism graphs

Archaellins assemble into a rotating motility filament (ASSEMBLY)

Prearchaellins are matured and glycosylated before archaellin subunits assemble into a helical extracellular filament that is rotated by the basal archaellum motor to generate archaeal swimming motility.

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.
prearchaellins	is processed into	mature archaellins	`DOI:10.3389/fmicb.2015.00023` Albers and Jarrell 2015 review prearchaellin processing and N-glycosylation before archaellin filament assembly.
mature archaellins	polymerize into	archaeal-type flagellum filament	`DOI:10.1038/s41467-022-28337-1` Gambelli et al. 2022 solved a Methanocaldococcus villosus filament made from alternating ArlB1 and ArlB2 subunits.
ArlI/ArlJ motor core	assembles and rotates	archaeal-type flagellum filament	`DOI:10.3389/fmicb.2015.00023` Albers and Jarrell 2015 review FlaI/ArlI as the ATPase that powers archaellum assembly and rotation.
archaeal-type flagellum filament	drives	archaeal-type flagellum-dependent cell motility	`DOI:10.3389/fmicb.2015.00023` Albers and Jarrell 2015 describe filament rotation as the basis of archaellum-dependent swimming.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral grounding for filament-forming archaellins. This first filament record follows reviewed Arl/Fla nomenclature but leaves the full archaellin subunit class label-only rather than asserting a broad type-IV pilin family or a lineage-specific archaellin accession as an exact source-neutral grounding.
INTERPRETATION (RESOLVED): ArlI/ArlJ motor proteins are associated assembly and rotation machinery rather than archaellum filament constituents. The filament is the extracellular polymer of archaellin subunits. The basal motor powers assembly and rotates the polymer but is not itself part of the filament.

Evidence

DOI:10.3389/fmicb.2015.00023 Albers SV and Jarrell KF 2015, The archaellum: how Archaea swim, Frontiers in Microbiology.
DOI:10.1038/s41467-022-28337-1 Gambelli L 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

2026-09-23T04:53:14Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-23T04:54:09Z codex · EXPANDED_RECORD — Added archaellum-filament synonymy, parentage, part_of the complete archaeal-type flagellum, label-only archaellin component curation, archaeal scope, Methanocaldococcus villosus example, swimming-motility function, DOI evidence, a nonmechanistic maturation-to-rotation graph, and grounding and motor-boundary discussions.
2026-09-23T05:05:13Z codex · REVIEW_FIX — Addressed PR review issues #1356 and #1357 by connecting prearchaellin processing to the mature archaellin node and retyping the ArlI/ArlJ motor-core graph node from GENE_OR_PROTEIN to STRUCTURE.
2026-10-10T07:08:28Z claude · ADDRESS_REVIEW — Addressed #2115: replaced bacterial absence with bounded 2025 experimental and inferred evidence, retaining archaeal graph scope. Preserved PROPOSED status.

Source: data/structures/appendage/archaeal_type_flagellum_filament.yaml