AlfA filament

cellstructuremech:alfa_filament · Cytoskeleton · Filament · Proposed

A plasmid-encoded bacterial actin-like cytoskeletal filament assembled from AlfA ATPases that supports segregation of pLS32-family plasmids in Bacillus subtilis. [DOI:10.1038/sj.emboj.7601443]

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
AlfA	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	alfA		ESSENTIAL	Plasmid-encoded actin-like ATPase subunit that polymerizes into filaments for pLS32-family plasmid segregation. `DOI:10.1038/sj.emboj.7601443` Becker et al. 2006 tied the Bacillus subtilis AlfA protein to actin-like filaments and active plasmid segregation. `DOI:10.1128/JB.00676-09` Polka et al. 2009 analyzed purified AlfA polymerization and filament ultrastructure.

Taxonomic distribution

NCBITaxon:1423 Bacillus subtilis — VARIABLE: AlfA is encoded by pLS32-family plasmid partition systems characterized in Bacillus subtilis; this record does not assert the filament across all Bacillus subtilis strains. [DOI:10.1038/sj.emboj.7601443]

Canonical examples

NCBITaxon:1423 Bacillus subtilis — Host species used to characterize AlfA filament formation and segregation of the pLS32-family miniplasmid pBET131. [DOI:10.1038/sj.emboj.7601443]

Functions

pLS32-family plasmid segregation — AlfA filaments work with the AlfB adaptor and the parN centromere to support active segregation of pLS32-family plasmid DNA in Bacillus subtilis.
- DOI:10.1038/sj.emboj.7601443 Becker et al. 2006 showed that AlfA is needed for active segregation of pBET131, a pLS32 derivative.
- DOI:10.1073/pnas.1304127111 Polka et al. 2014 connected AlfA dynamics to AlfB and parN-dependent plasmid positioning.

Mechanism graphs

AlfA filaments support pLS32-family plasmid segregation (FUNCTION)

AlfA polymerizes into actin-like filaments, and AlfB-parN plasmid-centromere complexes regulate filament organization to support active segregation of pLS32-family plasmids.

Subject	Predicate	Object	Evidence
AlfA	polymerizes into	AlfA filament	`DOI:10.1128/JB.00676-09` Polka et al. 2009 purified AlfA and analyzed its assembly into actin-like filaments. `DOI:10.1073/pnas.1716424115` Szewczak-Harris and Lowe 2018 solved a high-resolution AlfA filament cryo-EM reconstruction.
AlfB-parN plasmid-centromere complex	regulates	AlfA filament	`DOI:10.1073/pnas.1304127111` Polka et al. 2014 connected AlfA filament dynamics to AlfB and parN.
AlfA filament	supports	pLS32-family plasmid segregation	`DOI:10.1038/sj.emboj.7601443` Becker et al. 2006 connected AlfA filament formation to active pBET131 plasmid segregation. `DOI:10.1073/pnas.1304127111` Polka et al. 2014 characterized the AlfA-dependent plasmid-positioning system.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral grounding for pLS32-family AlfA actin-like ATPases. This first record curates AlfA from the Bacillus subtilis pLS32-family partition system without asserting that a broad actin ATPase or bacterial actin-like family accession exactly denotes filament-forming AlfA proteins.
INTERPRETATION (RESOLVED): AlfB and parN are graph-scoped centromere adaptors rather than AlfA filament constituents. AlfB bound to parN centromere DNA regulates AlfA filament organization in the partition system, but the component list keeps only the AlfA polymer subunit as a constituent of the filament itself.

Evidence

DOI:10.1038/sj.emboj.7601443 Becker et al. 2006, DNA segregation by the bacterial actin AlfA during Bacillus subtilis growth and development, EMBO Journal.
DOI:10.1128/JB.00676-09 Polka, Kollman, Agard and Mullins 2009, The Structure and Assembly Dynamics of Plasmid Actin AlfA Imply a Novel Mechanism of DNA Segregation, Journal of Bacteriology.
DOI:10.1073/pnas.1304127111 Polka et al. 2014, Accessory factors promote AlfA-dependent plasmid segregation by regulating filament nucleation, disassembly, and bundling, PNAS.
DOI:10.1073/pnas.1716424115 Szewczak-Harris and Lowe 2018, Cryo-EM reconstruction of AlfA from Bacillus subtilis reveals the structure of a simplified actin-like filament at 3.4-A resolution, PNAS.
DOI:10.1128/JB.01312-09 Tanaka 2010, Functional analysis of the stability determinant AlfB of pBET131, a miniplasmid derivative of Bacillus subtilis (natto) plasmid pLS32, Journal of Bacteriology.
GO:0099513 — polymeric cytoskeletal fiber Polymeric cytoskeletal fiber is the broader class for a filament assembled from AlfA protein subunits, not an exact AlfA identity.
GO:0005856 — cytoskeleton Cytoskeleton is the containing framework; GO places polymeric cytoskeletal fiber part_of this structure, not is_a.

Curation history

2026-09-22T04:22:36Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-22T04:25:05Z codex · EXPANDED_RECORD — Added cytoskeleton parentage, AlfA component curation, Bacillus subtilis pLS32-family plasmid scope, a pLS32-family plasmid segregation function, DOI evidence, a nonmechanistic AlfA/AlfB/parN graph, and AlfA grounding and AlfB/parN boundary discussions.
2026-09-22T04:26:00Z codex · FIX_CITATION_NOTE — Corrected the Polka et al. 2014 AlfB/parN citation title.
2026-09-22T06:44:02Z codex · REMOVE_UNATTESTED_SYNONYM — Removed the paraphrased plasmid actin AlfA filament related synonym; the cited paper describes AlfA as a plasmid actin but does not attest that full phrase as an alternate filament label.
2026-09-22T07:01:00Z codex · REVIEW_FIX — Addressed PR review issues #1265 and #1266 by correcting the Tanaka AlfB citation note and simplifying the AlfB/parN graph to a graph-scoped centromere-complex adapter node.
2026-10-11T07:14:22Z codex · ADDRESS_SAVED_REVIEW — Addressed #2190, #2191, #2192: Replaced four ParM DOI miscitations with the intended AlfA paper, corrected the journal and Becker author attribution, and separated filament is-a from cytoskeleton parthood without changing the minted identity.

Source: data/structures/cytoskeleton/alfa_filament.yaml