MreB filament

cellstructuremech:mreb_filament · Cytoskeleton · Filament · Proposed

The actin-like cytoskeletal filament of rod-shaped bacteria. MreB polymerises into short membrane-associated filaments that circle the cell at an angle to its long axis and move processively around it, carrying the elongasome — the peptidoglycan synthases that widen the sidewall — so that new wall material is inserted where the filaments travel. It is a homologue of eukaryotic actin by fold, not by sequence identity. [DOI:10.1016/j.cell.2018.02.050]

Synonyms: bacterial actin

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
MreB	Protein	part of		mreB		ESSENTIAL	The filament subunit; an actin-fold ATPase that polymerises into short antiparallel double filaments on the membrane. `DOI:10.1146/annurev-genet-102108-134845` The Bacterial Cytoskeleton (2010) describes MreB as the actin homologue of rod-shaped bacteria. `DOI:10.1016/j.cell.2018.02.050` Shi et al. 2018 review MreB filament architecture and its membrane association.
RodZ	Protein	acts on		rodZ		CONDITIONAL	Bridges the filament to the elongasome, the sidewall-synthesis machine the filament guides. MreC and MreD were listed here until #102: they are constituents of that machine, not of this filament, and now live on the elongasome record. `DOI:10.1016/j.cell.2018.02.050` Shi et al. 2018 describe RodZ coupling MreB to the synthetic complex.

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.

MreB

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0A9X4`	Cell shape-determining protein MreB	mreB	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene mreB in Escherichia coli K-12, 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:15612918` Kruse T et al. 2005, ‘The morphogenetic MreBCD proteins of Escherichia coli form an essential membrane-bound complex.’, Mol Microbiol. ECO:0000269 experimental evidence cited by UniProt for the 'Cytoplasm' localisation of P0A9X4.

RodZ

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P27434`	Cytoskeleton protein RodZ	rodZ	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene rodZ in Escherichia coli K-12, a taxon this record names; other reviewed entries for this symbol exist on sub-strain nodes and this is the one at the taxon the record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `PMID:19008860` Shiomi D et al. 2008, ‘Determination of bacterial rod shape by a novel cytoskeletal membrane protein.’, EMBO J. ECO:0000269 experimental evidence cited by UniProt for the 'Cell inner membrane' localisation of P27434.

Taxonomic distribution

NCBITaxon:2 Bacteria — VARIABLE: Present in many rod-shaped and curved lineages and absent from most cocci, but the correlation is not tight: Actinobacteria and Rhizobiales are rod-like or curved and lack MreB altogether. [DOI:10.1016/j.cell.2018.02.050]

Canonical examples

NCBITaxon:83333 Escherichia coli K-12 — The system in which filament motion was shown to be driven by wall synthesis. [DOI:10.1016/j.cell.2018.02.050]
NCBITaxon:1423 Bacillus subtilis — Reference Gram-positive elongasome. [DOI:10.1146/annurev-genet-102108-134845]

Functions

regulation of cell shape GO:0008360 — Directs where sidewall peptidoglycan is inserted, maintaining a rod.
- DOI:10.1016/j.cell.2018.02.050 Shi et al. 2018 review MreB's role in organising sidewall synthesis and rod shape.
- DOI:10.1146/annurev-genet-102108-134845 The Bacterial Cytoskeleton (2010) links mreB loss to loss of rod shape.

Associated traits

REQUIRED_FOR METPO:1000681 rod shaped
- DOI:10.1016/j.cell.2018.02.050 — MreB depletion results in loss of rod-like shape and rounding (Kruse et al., 2005), and there are no E. coli mutants or growth conditions known to restore rod-like shape in the absence of MreB. Verbatim from the open-access full text (PMC5846203). Supports REQUIRED_FOR rather than CONFERS: the shape is lost without MreB, and nothing restores it, but MreB alone does not produce a rod.
- DOI:10.1016/j.cell.2018.02.050 — Many rod-like and curved bacterial species require MreB to elongate, although there are exceptions such as the Actinobacteria and Rhizobiales that lack MreB altogether. The same source bounds the claim: rod shape can be achieved without MreB in some lineages, so the requirement is not universal across bacteria.
MODULATES METPO:1000666 cell shape
- DOI:10.1016/j.cell.2018.02.050 — MreB both senses and changes cell shape, thereby generating a self-organizing feedback system for shape maintenance. Verbatim from the open-access full text (PMC5846203). MODULATES rather than CONFERS: the filament is described as sensing and adjusting shape, not dictating it.

Mechanism graphs

MreB and RodZ orient sidewall synthesis to preserve a rod (FUNCTION)

MreB subunits form membrane-associated filaments that RodZ couples to the elongasome. Those filaments orient circumferential sidewall peptidoglycan synthesis, and the resulting feedback keeps rod-shaped cells from widening into spheres.

Subject	Predicate	Object	Evidence
MreB	polymerizes into	MreB filament	`DOI:10.1016/j.cell.2018.02.050` Shi, Bratton, Gitai and Huang 2018 review E. coli MreB filament architecture and membrane association.
RodZ	couples	elongasome	`DOI:10.1016/j.cell.2018.02.050` Shi, Bratton, Gitai and Huang 2018 review cytoplasmic RodZ-MreB binding and periplasmic RodZ contacts with wall-synthesis enzymes.
MreB filament	orients	elongasome	`DOI:10.1016/j.cell.2018.02.050` Shi, Bratton, Gitai and Huang 2018 describe MreB as a curvature sensor that both detects and changes local shape.
elongasome	carries out	peptidoglycan biosynthetic process	`DOI:10.1038/nrmicro2677` Typas, Banzhaf, Gross and Vollmer 2011 review the elongation complex that builds sidewall peptidoglycan. `DOI:10.1038/nmicrobiol.2016.172` Cho et al. 2016 use E. coli cell-wall synthesis and MreB-motion experiments to support a RodA/PBP2 synthase pair in the Rod system; the earlier 2011 review supplies broader elongation context.
peptidoglycan biosynthetic process	maintains	rod shaped	`DOI:10.1016/j.cell.2018.02.050` Shi, Bratton, Gitai and Huang 2018 describe MreB-driven cell-wall feedback as the self-organizing system for rod shape maintenance.

Discussions

CURATION_TODO (OPEN): This is the corpus's first minted identifier — is the scheme right? GO has no cellular-component term for MreB or for a bacterial actin cytoskeleton, so docs/CURATION.md requires minting with the nearest broader term as a parent. The local part is a lowercase slug of the label rather than a counter, because a slug needs no allocator and reads in a URL; the cost is that it looks stale if the preferred label ever changes, which is acceptable since identifiers are never renamed.
KNOWLEDGE_GAP (OPEN): The filament guides the elongasome, and the schema has no relation that says so. MreB filaments carry the RodA-PBP2 synthases around the cell; that is the point of the structure. It was briefly recorded as xrefs: [cellstructuremech:elongasome], but the schema defines xrefs as true equivalence and the two are not equivalent, so the claim was false as written and removed (#119). Until a relation exists, the link lives in the RodZ component role and in this discussion.
INTERPRETATION (RESOLVED): Bound archaeal homology separately from occurrence of this MreB filament system. The earlier Archaea RARE row cited actin-fold proteins, while its own note identified the MreB-elongasome arrangement as bacterial. Homology alone does not establish the occurrence or prevalence of the bacterial filament system defined in this record. Archaeal actin-like Ta0583 polymerization is a distinct experimental observation, not proof of this MreB-elongasome system.

Evidence

DOI:10.1146/annurev-genet-102108-134845 'The Bacterial Cytoskeleton', Annual Review of Genetics 2010.
DOI:10.1016/j.cell.2018.02.050 Shi H, Bratton BP, Gitai Z, Huang KC 2018, 'How to Build a Bacterial Cell: MreB as the Foreman of E. coli Construction', Cell.
GO:0099513 — polymeric cytoskeletal fiber Broader polymeric cytoskeletal fiber class; this protein filament retains its specific local identity.
GO:0005856 — cytoskeleton The cytoskeletal framework contains this filament; the filament is part of it, not a type of the entire framework.
DOI:10.1038/nmicrobiol.2016.172 Cho et al. 2016, Bacterial cell wall biogenesis is mediated by SEDS and PBP polymerase families functioning semi-autonomously, Nature Microbiology. Primary support for the Rod-system synthase-pair claim.

Curation history

2026-09-01T03:41:49Z claude · CREATED_RECORD — Drafted from the cited reviews; every GO term, taxon id and DOI resolved live before writing. Not yet human-reviewed.
2026-09-01T03:49:36Z claude · ADD_TRAIT_LINKS — Self-review of PR #101: linked the TraitMech phenotypes the filament confers (METPO:1000681 rod shaped, METPO:1000666 cell shape), which is the whole point of the structure and was missing.
2026-09-02T04:50:12Z claude · RESCOPE_COMPONENTS — #102: MreC and MreD moved to the new elongasome record, where they are constituents; the component here is narrowed to RodZ, which genuinely acts on the assembled filament. The elongasome is now cross-referenced.
2026-09-02T04:57:03Z claude · REMOVE_MISUSED_XREF — #119: removed xrefs: [cellstructuremech:elongasome]. xrefs means equivalence and the filament is not equivalent to the machine it guides; the relationship is stated in the component role and a discussion instead.
2026-09-02T06:07:45Z claude · ADD_VERBATIM_EVIDENCE — Replaced paraphrase-only attributions on both trait links with verbatim snippets from the open-access full text of Shi et al. 2018 (PMC5846203), which I read for this purpose. Dropped the Annual Review of Genetics 2010 citation from the cell-shape link: it has no PubMed or PMC record, so nothing of it could be read beyond a Crossref title, and citing it for a specific claim was not supportable. Reading the source also bounded a taxonomic claim: the record said shape and mreB track each other, and the same paper names Actinobacteria and Rhizobiales as rod-like lineages without MreB.
2026-09-02T20:18:15Z claude · CORRECT_CURATION_EVENT — #145: the ADD_VERBATIM_EVIDENCE event above states that DOI:10.1146/annurev-genet-102108-134845 has no PubMed or PMC record. That is false: it is PMID 21047262 and its abstract is available. The check behind the claim asked only NCBI's PMC id converter, which indexes PMC alone, and read its empty response as absence from PubMed too; Europe PMC returns the record directly. The event is left standing rather than rewritten, because curation_history is append-only and hiding an error is worse than the error. The removal it describes still holds on its own ground: the paraphrase was written without reading the paper, and the abstract does not carry the specific cell-shape claim it was attached to. The paper remains cited elsewhere on this record, and the three verbatim snippets are unaffected.
2026-09-04T00:58:09Z codex · ADD_CAUSAL_GRAPH — Added a FUNCTION graph for MreB/RodZ-guided sidewall synthesis that points at the separate elongasome record, cites the existing MreB shape review and the elongasome's sidewall-synthesis review, and keeps the filament-to-machine relation out of equivalence-only xrefs.
2026-09-08T07:38:55Z uniprot_genes · SEED_PROTEIN_EXAMPLES — #183: added 2 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.
2026-10-11T18:52:14Z codex · ADDRESS_SAVED_REVIEW — Addressed #2237, #2238, #2239: Corrected cytoskeletal fiber is-a and containing-framework parthood. Removed the unsupported affirmative Archaea RARE row and appended a scope discussion distinguishing actin-fold homology from evidence for this bacterial filament system. This is not an archaeal absence claim. Definition now cites the inspected 2018 review; the RodA/PBP2 synthesis edge also cites the 2016 primary experiments. Earlier bibliography, graph relations and verbatim trait evidence remain intact.

Source: data/structures/cytoskeleton/mreb_filament.yaml